bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒02‒16
38 papers selected by
Richard Halfpenny
Staffordshire University


  1. J Med Entomol. 2020 Feb 12. pii: tjaa010. [Epub ahead of print]
    Grant GG, Estrera RR, Pathak N, Hall CD, Tsikolia M, Linthicum KJ, Bernier UR, Hall AC.
      The carboxamide N,N-di-ethyl-meta-toluamide (DEET) is the most effective and widely used insect repellent today. However, drawbacks concerning the efficacy and the safety of the repellent have led to efforts to design new classes of insect repellents. Through quantitative structure-activity relationships, chemists have discovered two chemical groups of novel repellents: the acylpiperidines and the carboxamides, with the acylpiperidines generally more potent in biological assays. Although the exact mechanism of action of DEET and other repellents has not yet been thoroughly elucidated, previous research shows that the activity of insect odorant receptors are inhibited in the presence of repellents. The present electrophysiological study employs two-electrode voltage clamp with Xenopus laevis oocytes expressing AgOR2/AgOrco and AgOR8/AgOrco receptors to assess the effects of the novel repellents on Anopheles gambiae Giles (Insecta: Diptera: Culicidae) mosquito odorant receptors. The novel acylpiperidines and carboxamides reversibly inhibited (12-91%) odorant-evoked currents from both AgOR2/AgOrco and AgOR8/AgOrco receptors in a dose-dependent manner at all tested concentrations (30 μM to 1 mM). Furthermore, all the novel agents were more potent inhibitors of the receptors than DEET, with the acylpiperidines producing on average greater inhibition than the carboxamides. Interestingly, there was a correlation (r2 = 0.72) between the percentage inhibition of AgOR2/AgOrco receptor currents and protection times of the acylpiperidines. Our results add to existing evidence that the repellency of a compound is linked to its ability to disrupt the insect olfactory system and that the acylpiperidines could represent a class of more effective alternatives to the current gold standard, DEET.
    Keywords:   odorant; DEET; oocyte; receptor; repellent
    DOI:  https://doi.org/10.1093/jme/tjaa010
  2. J Med Entomol. 2020 Feb 11. pii: tjaa005. [Epub ahead of print]
    Olson MF, Garcia-Luna S, Juarez JG, Martin E, Harrington LC, Eubanks MD, Badillo-Vargas IE, Hamer GL.
      Effective mosquito surveillance and management depend on a thorough understanding of the biology and feeding patterns unique to species and sex. Given that a propensity to sugar feed is necessary for some mosquito surveillance and newer control strategies, we sought to document the amount of total sugar in wild Aedes aegypti (L.) and Culex quinquefasciatus (Say) captured from five different locations in the Lower Rio Grande Valley (LRGV) of South Texas over 2 yr. We used Biogents Sentinel 2 (BGS2) traps in year 1 and aspirators, BGS2, and CDC resting traps in years 2 and 3 to collect adult mosquitoes. The hot anthrone test was used to quantify total sugar content in each mosquito. Additionally, the cold and hot anthrone tests were used to distinguish fructose content from total sugars for mosquitoes captured in 2019. Overall, Ae. aegypti females had significantly lower total sugar content than Ae. aegypti males as well as both sexes of Cx. quinquefasciatus. However, the percentage of Ae. aegypti positive for fructose consumption was four to eightfold higher than Ae. aegypti previously reported in other regions. The difference between locations was significant for males of both species, but not for females. Seasonality and trapping method also revealed significant differences in sugar content of captured mosquitoes. Our results reinforce that sugar feeding in female Ae. aegypti is less than Cx. quinquefasciatus, although not absent. This study provides necessary data to evaluate the potential effectiveness of sugar baits in surveillance and control of both Ae. aegypti and Cx. quinquefasciatus mosquitoes.
    Keywords:   Aedes ; Culex ; collection method; sugar-feeding; surveillance
    DOI:  https://doi.org/10.1093/jme/tjaa005
  3. Malar J. 2020 Feb 14. 19(1): 72
    Traore MM, Junnila A, Traore SF, Doumbia S, Revay EE, Kravchenko VD, Schlein Y, Arheart KL, Gergely P, Xue RD, Hausmann A, Beck R, Prozorov A, Diarra RA, Kone AS, Majambere S, Bradley J, Vontas J, Beier JC, Müller GC.
      BACKGROUND: The aim of this field trial was to evaluate the efficacy of attractive toxic sugar baits (ATSB) in Mali, where sustained malaria transmission occurs despite the use of long-lasting insecticidal nets (LLINs). ATSB bait stations were deployed in seven of 14 similar study villages, where LLINs were already in widespread use. The combined use of ATSB and LLINs was tested to see if it would substantially reduce parasite transmission by Anopheles gambiae sensu lato beyond use of LLINs alone.METHODS: A 2-day field experiment was conducted to determine the number of mosquitoes feeding on natural sugar versus those feeding on bait stations containing attractive sugar bait without toxin (ASB)-but with food dye. This was done each month in seven random villages from April to December 2016. In the following year, in seven treatment villages from May to December 2017, two ATSB bait stations containing the insecticide dinotefuran were placed on the outer walls of each building. Vector population density was evaluated monthly by CDC UV light traps, malaise traps, pyrethrum spray (PSCs) and human landing catches (HLCs). Female samples of the catch were tested for age by examination of the ovarioles in dissected ovaries and identification of Plasmodium falciparum sporozoite infection by ELISA. Entomological inoculation rates (EIR) were calculated, and reductions between treated and untreated villages were determined.
    RESULTS: In the 2-day experiment with ASB each month, there was a lower number of male and female mosquitoes feeding on the natural sugar sources than on the ASB. ATSB deployment reduced CDC-UV trap female catches in September, when catches were highest, were by 57.4% compared to catches in control sites. Similarly, malaise trap catches showed a 44.3% reduction of females in August and PSC catches of females were reduced by 48.7% in September. Reductions of females in HLCs were lower by 19.8% indoors and 26.3% outdoors in September. The high reduction seen in the rainy season was similar for males and reductions in population density for both males and females were > 70% during the dry season. Reductions of females with ≥ 3 gonotrophic cycles were recorded every month amounting to 97.1% in October and 100.0% in December. Reductions in monthly EIRs ranged from 77.76 to 100.00% indoors and 84.95% to 100.00% outdoors. The number of sporozoite infected females from traps was reduced by 97.83% at treated villages compared to controls.
    CONCLUSIONS: Attractive toxic sugar baits used against Anopheles mosquitoes in Mali drastically reduced the density of mosquitoes, the number of older females, the number of sporozoite infected females and the EIR demonstrating how ATSB significantly reduces malaria parasite transmission.
    Keywords:  ATSB; Anopheles gambiae; Mali; Sugar feeding; Vector control
    DOI:  https://doi.org/10.1186/s12936-020-3132-0
  4. Parasitol Res. 2020 Feb 08.
    Fălcuţă E, Prioteasa LF, Horváth C, Păstrav IR, Schaffner F, Mihalca AD.
      Currently, five invasive Aedes mosquito species are of concern in Europe according to the European Centre for Disease Prevention and Control: Aedes aegypti, Ae. albopictus, Ae. atropalpus, Ae. japonicus, and Ae. koreicus. Among these, only Ae. albopictus was reported to occur in Romania, in Bucharest. The aim of this study was to update the knowledge on the distribution of this invasive mosquito species in Romania, by investigating new potential locations. Monitoring of Ae. albopictus was carried out between May 2017 and October 2018. Three types of traps (CDC-Gravid Traps, CDC miniature Light Traps, ovitraps) were placed in 53 localities in 13 counties at sites suitable for container-breeding mosquitoes. Collected adult mosquitoes were counted and identified according to morphological criteria. Larvae were found present in domestic containers and rain catch basins. Aedes albopictus adults and eggs were collected in 10 localities in eight counties across Romania. Our study confirms nine new localities and seven counties where Ae. albopictus became established in Romania, highlighting the need for surveillance to further assess the species' distribution and abundance, as well as the pathogen transmission risk related to that vector species.
    Keywords:  Aedes albopictus; Invasive species; Mosquitoes; New records; Tiger mosquito
    DOI:  https://doi.org/10.1007/s00436-020-06620-8
  5. Mem Inst Oswaldo Cruz. 2020 ;pii: S0074-02762020000100400. [Epub ahead of print]115 e190390
    Cardo MV, Rubio A, Vezzani D, Carbajo AE.
      The mosquito Culex pipiens s.s. L. occurs as two bioforms that differ in physiology and behaviour affecting virus transmission cycles. To assess the occurrence of Cx. pipiens bioforms in the southernmost limit of its distribution, specimens were collected aboveground in southern Buenos Aires Province and east Patagonia, Argentina. Ten larvae and 25 adults were individually processed and identified by polymerase chain reaction (PCR) amplification of Ace-2 and CQ11 loci. Culex quinquefasciatus Say (one larva, two adults), Cx. pipiens f. molestus (one larva, one adult) and one adult of hybrid origin were identified in Buenos Aires Province; only Cx. pipiens f. molestus was recorded in Patagonia (eight larvae, 21 adults). The potential absence of bioform pipiens and its implications in arbovirus enzootic cycles is discussed.
    DOI:  https://doi.org/10.1590/0074-02760190390
  6. Front Immunol. 2019 ;10 3072
    Tang J, Templeton TJ, Cao J, Culleton R.
      The distributions of human malaria parasite species overlap in most malarious regions of the world, and co-infections involving two or more malaria parasite species are common. Little is known about the consequences of interactions between species during co-infection for disease severity and parasite transmission success. Anti-malarial interventions can have disproportionate effects on malaria parasite species and may locally differentially reduce the number of species in circulation. Thus, it is important to have a clearer understanding of how the interactions between species affect disease and transmission dynamics. Controlled competition experiments using human malaria parasites are impossible, and thus we assessed the consequences of mixed-species infections on parasite fitness, disease severity, and transmission success using the rodent malaria parasite species Plasmodium chabaudi, Plasmodium yoelii, and Plasmodium vinckei. We compared the fitness of individual species within single species and co-infections in mice. We also assessed the disease severity of single vs. mixed infections in mice by measuring mortality rates, anemia, and weight loss. Finally, we compared the transmission success of parasites in single or mixed species infections by quantifying oocyst development in Anopheles stephensi mosquitoes. We found that co-infections of P. yoelii with either P. vinckei or P. chabaudi led to a dramatic increase in infection virulence, with 100% mortality observed in mixed species infections, compared to no mortality for P. yoelii and P. vinckei single infections, and 40% mortality for P. chabaudi single infections. The increased mortality in the mixed infections was associated with an inability to clear parasitaemia, with the non-P. yoelii parasite species persisting at higher parasite densities than in single infections. P. yoelii growth was suppressed in all mixed infections compared to single infections. Transmissibility of P. vinckei and P. chabaudi to mosquitoes was also reduced in the presence of P. yoelii in co-infections compared to single infections. The increased virulence of co-infections containing P. yoelii (reticulocyte restricted) and P. chabaudi or P. vinckei (predominantly normocyte restricted) may be due to parasite cell tropism and/or immune modulation of the host. We explain the reduction in transmission success of species in co-infections in terms of inter-species gamete incompatibility.
    Keywords:  Plasmodium chabaudi; Plasmodium vinckei; Plasmodium yoelii; co-infections; malaria; mixed-species; virulence
    DOI:  https://doi.org/10.3389/fimmu.2019.03072
  7. J Infect Dev Ctries. 2019 Mar 31. 13(3): 233-239
    Mohammed H, Hayden MH, Lee E, Santiago LM, Krecek RC, Revan F, Hunsperger E.
      INTRODUCTION: After a large outbreak of dengue virus (DENV) serotype-3 in Saint Kitts and Nevis (SKN) in 2008, we performed a cross-sectional study to determine the prevalence of anti-DENV immunoglobulin G (IgG) antibodies in expatriate and local persons affiliated with an American veterinary school there.METHODOLOGY: This campus community comprised mostly expatriate students and faculty and Kittitian administrative staff. In 2009, a stratified random sample of students, faculty and staff was invited to complete an electronic survey to assess risk factors for DENV and provide blood for testing for anti-DENV IgG antibodies by an enzyme-linked immunosorbent assay. IgG-positive specimens were also tested by a 90% plaque reduction neutralization test (PRNT90) to determine immunoreactivity to DENV (1-4) serotypes and West Nile virus. Risk factors for anti-DENV IgG seropositivity were determined using simple and adjusted logistic regression.
    RESULTS: Of the 118 participants, the overall prevalence of DENV IgG antibodies was 44.1% (95% confidence interval [CI]: 35.1-53.0%), ranging from 30.1% in students, 100.0% in staff and 57.9% in faculty (p < 0.001). Duration of residence in St. Kitts was the only variable significantly associated with seropositivity on multiple logistic regression (adjusted odds ratio [95% CI]: 1.21 [1.07-1.37]). The serotype of DENV was determined in 11 persons: DENV-1 (n = 4), DENV-2 (n = 3), and DENV-3 (n = 4).
    CONCLUSIONS: Expatriate students and faculty moving to St. Kitts from non-endemic areas were at high risk of DENV infection. There is a need for increased emphasis on pre-travel mosquito-borne virus prevention education for persons moving to St. Kitts to study and work.
    Keywords:  Saint Kitts and Nevis; dengue; fever; travellers
    DOI:  https://doi.org/10.3855/jidc.10701
  8. Parasit Vectors. 2020 Feb 10. 13(1): 54
    Ekwudu O, Devine GJ, Aaskov JG, Frentiu FD.
      BACKGROUND: Wolbachia pipientis are bacterial endosymbionts of arthropods currently being implemented as biocontrol agents to reduce the global burden of arboviral diseases. Some strains of Wolbachia, when introduced into Aedes aegypti mosquitoes, reduce or block the replication of RNA viruses pathogenic to humans. The wAlbB strain of Wolbachia was originally isolated from Aedes albopictus, and when transinfected into Ae. aegypti, persists in mosquitoes under high temperature conditions longer than other strains. The utility of wAlbB to block a broad spectrum of RNA viruses has received limited attention. Here we test the ability of wAlbB to reduce or block the replication of a range of Flavivirus and Alphavirus species in cell culture.METHODS: The C6/36 mosquito cell line was stably infected with the wAlbB strain using the shell-vial technique. The replication of dengue, West Nile and three strains of Zika (genus Flavivirus), and Ross River, Barmah Forest and Sindbis (genus Alphavirus) viruses was compared in wAlbB-infected cells with Wolbachia-free controls. Infectious virus titres were determined using either immunofocus or plaque assays. A general linear model was used to test for significant differences in replication between flaviviruses and alphaviruses.
    RESULTS: Titres of all viruses were significantly reduced in cell cultures infected with wAlbB versus Wolbachia-free controls. The magnitude of reduction in virus yields varied among virus species and, within species, also among the strains utilized.
    CONCLUSION: Our results suggest that wAlbB infection of arthropods could be used to reduce transmission of a wide range of pathogenic RNA viruses.
    Keywords:  Arbovirus; Dengue; Mosquito; Ross River Virus; Sindbis; West Nile; Zika
    DOI:  https://doi.org/10.1186/s13071-020-3936-3
  9. Bull Math Biol. 2020 Feb 12. 82(2): 32
    Mehra S, McCaw JM, Flegg MB, Taylor PG, Flegg JA.
      Malaria is an infectious disease with an immense global health burden. Plasmodium vivax is the most geographically widespread species of malaria. Relapsing infections, caused by the activation of liver-stage parasites known as hypnozoites, are a critical feature of the epidemiology of Plasmodium vivax. Hypnozoites remain dormant in the liver for weeks or months after inoculation, but cause relapsing infections upon activation. Here, we introduce a dynamic probability model of the activation-clearance process governing both potential relapses and the size of the hypnozoite reservoir. We begin by modelling activation-clearance dynamics for a single hypnozoite using a continuous-time Markov chain. We then extend our analysis to consider activation-clearance dynamics for a single mosquito bite, which can simultaneously establish multiple hypnozoites, under the assumption of independent hypnozoite behaviour. We derive analytic expressions for the time to first relapse and the time to hypnozoite clearance for mosquito bites establishing variable numbers of hypnozoites, both of which are quantities of epidemiological significance. Our results extend those in the literature, which were limited due to an assumption of collective dormancy. Our within-host model can be embedded readily in multiscale models and epidemiological frameworks, with analytic solutions increasing the tractability of statistical inference and analysis. Our work therefore provides a foundation for further work on immune development and epidemiological-scale analysis, both of which are important for achieving the goal of malaria elimination.
    Keywords:  Activation–clearance; Continous time Markov chain; Hypnozoite; Relapse; Vivax
    DOI:  https://doi.org/10.1007/s11538-020-00706-1
  10. Trop Med Health. 2020 ;48 5
    Adhikari N, Subedi D.
      Dengue is a mosquito-borne viral infection. Since the first reported incidence in 2004, several sporadic outbreaks of dengue have been recorded from both tropical and subtropical regions of Nepal, including the capital city Kathmandu. However, in the last 5 years, the incidence of dengue cases has risen alarmingly. The largest-ever outbreak was reported in 2019, which killed six people. The global warming, unplanned urbanization, increased transportation, and lack of efficient mosquito control are presumably associated with the spread of dengue and its vector to the plane and hilly regions of this country. With the ongoing Nepalese government campaign "Visit Nepal Year 2020" to attract two million tourists in mind, effective dengue control measures must be implemented to control potential future outbreaks.
    Keywords:  Alarming outbreaks; Control; Dengue; Nepal; Visit Nepal Year 2020
    DOI:  https://doi.org/10.1186/s41182-020-0194-1
  11. Emerg Microbes Infect. 2020 Dec;9(1): 348-365
    Nazareth T, Craveiro I, Moutinho A, Seixas G, Gonçalves C, Gonçalves L, Teodósio R, Sousa CA.
      The release of modified mosquitoes to suppress/replace vectors constitutes a promising tool for vector control and disease prevention. Evidence regarding these innovative modification techniques is scarce and disperse. This work conducted a systematic review, gathering and analysing research articles from PubMed and Biblioteca Virtual em Saúde databases whose results report efficacy and non-target effects of using modified insects for disease prevention, until 2016. More than 1500 publications were screened and 349 were analysed. Only 12/3.4% articles reported field-based evidence and 41/11.7% covered modification strategies' post-release efficacy. Variability in the effective results (90/25.7%) questioned its reproducibility in different settings. We also found publications reporting reversal outcomes 38/10.9%, (e.g. post-release increase of vector population). Ecological effects were also reported, such as horizontal transfer events (54/15.5%), and worsening pathogenesis induced by natural wolbachia (10/2.9%). Present work revealed promising outcomes of modifying strategies. However, it also revealed a need for field-based evidence mainly regarding epidemiologic and long-term impact. It pointed out some eventual irreversible and important effects that must not be ignored when considering open-field releases, and that may constitute constraints to generate the missing field evidence. Present work constitutes a baseline of knowledge, offering also a methodological approach that may facilitate future updates.
    Keywords:  Vector-borne diseases; Wolbachia; genetically modified mosquitoes; transgenesis
    DOI:  https://doi.org/10.1080/22221751.2020.1722035
  12. Sci Rep. 2020 Feb 11. 10(1): 2378
    Nyberg HJ, Muto K.
      Acoustic larviciding (AL) occurs by exposing mosquito larvae to acoustic energy that ruptures their dorsal tracheal trunks (DTTs) by the expulsion of gas bubbles into the body. In studying this technique, we serendipitously identified undescribed anatomical and physiological respiratory features. The classical theory of respiration is that the siphon and DTTs play obligate roles in respiration. Our results contradict the accepted theory that culicine larvae respire via atmospheric gas exchange. We identified an undescribed tracheal occlusion (TO) at the posterior extremities the DTTs. The TOs appear necessary for the acoustic rupture of DTTs; this constriction prevents the escape of energized gas from the siphon and allows the tracheal system to be pressurized. With a pressurized isolated tracheal system, metabolic gas exchange directly with the atmosphere is unlikely and could mostly occur through the chitin and setae. Future studies are needed to explore respiration and elucidate the mechanisms of oxygen absorption and carbon dioxide elimination.
    DOI:  https://doi.org/10.1038/s41598-020-59321-8
  13. Trans R Soc Trop Med Hyg. 2020 Feb 11. pii: trz134. [Epub ahead of print]
    Ngwe Tun MM, Hmone SW, Soe AM, Luvai E, Nwe KM, Inoue S, Buerano CC, Thant KZ, Morita K.
      BACKGROUND: Zika virus (ZIKV) is a mosquito-borne flavivirus. Outbreaks of ZIKV infection have occurred in Africa, Southeast Asia, the Pacific Islands, the Americas and the Caribbean. Although most ZIKV infections are asymptomatic, cases of neurological manifestations have been described. The aim of the present study was to identify the prevalence of ZIKV infection among the asymptomatic persons in Myanmar in 2018.METHODS: A total of 284 serum samples from apparently healthy persons were collected from Yangon, Myanmar in 2018. They were analysed for ZIKV infection by immunoglobulin M (IgM) capture enzyme-linked immunosorbent assay (ELISA), IgG indirect ELISA, 50% focus reduction neutralization test, real-time reverse transcription polymerase chain reaction (RT-PCR) and conventional RT-PCR.
    RESULTS: Of the 284 apparently healthy persons, 31.3% were positive for the presence of IgM against ZIKV and 94.3% were positive for anti-flavivirus IgG. Among the ZIKV IgM-positive samples, we confirmed ZIKV infection in 15.8% of asymptomatic persons by neutralization test and real-time RT-PCR.
    CONCLUSIONS: We conclude that ZIKV infection was increasing among asymptomatic persons in the same area in Myanmar during 2018 compared with 2017. It is highly recommended to strengthen the surveillance system for ZIKV to prevent possible outbreaks.
    Keywords:  ELISA; Myanmar; Zika Virus; asymptomatic persons; neutralization test; real-time RT-PCR
    DOI:  https://doi.org/10.1093/trstmh/trz134
  14. Public Health Rep. 2020 Feb 10. 33354920904068
    Johnston DI, Viray MA, Ushiroda JM, He H, Whelen AC, Sciulli RH, Kunimoto GY, Y Park S.
      OBJECTIVES: From September 2015 through March 2016, Hawaii had the largest outbreak of locally transmitted dengue since 1944. We report on the Hawaii Department of Health's (HDOH's) investigation, findings, and response to the outbreak.METHODS: We defined cases of dengue using a modified version of the Council of State and Territorial Epidemiologists' case definition for dengue virus infections. We conducted epidemiologic investigations, including interviews with case-persons, review of medical records, laboratory testing, genetic sequencing of specimens, and geographic information system (GIS) data analysis. Outbreak response included community outreach and vector-control activities.
    RESULTS: We identified 264 confirmed cases of dengue; illness onset dates ranged from September 11, 2015, to March 17, 2016, all with reported travel to or residence on the Island of Hawaii. Of 264 persons with confirmed dengue, 238 (90.2%) were Hawaii residents. Thirty-seven (14.0%) persons required hospitalization; no cases of severe dengue or death were reported. GIS hot-spot analysis identified a cluster of cases on the western side of the island. Established risk factors for dengue exposure included holes in window or door screens, presence of standing water, and not using insect repellent or wearing protective clothing.
    CONCLUSIONS: To prevent or mitigate the spread of future arboviral introductions and outbreaks, the public health response should focus on behavioral and cultural attitudes, emphasizing personal mosquito protection and mosquito control at the community level. Outbreak responses can also be enhanced through the use of advanced GIS techniques, such as hot-spot analysis, to provide situational awareness and guide response efforts.
    Keywords:  Hawaii; arthropod-borne viruses; break-bone fever; dengue fever
    DOI:  https://doi.org/10.1177/0033354920904068
  15. Int J Environ Res Public Health. 2020 Feb 11. pii: E1127. [Epub ahead of print]17(4):
    Weinstein JS, Leslie TF, von Fricken ME.
      Land use boundaries represent human-physical interfaces where risk of vector-borne disease transmission is elevated. Land development practices, coupled with rural and urban land fragmentation, increases the likelihood that immunologically naïve humans will encounter infectious vectors at land use interfaces. This research consolidated land use classes from the GLC-SHARE dataset; calculated landscape metrics in linear (edge) density, proportion abundance, and patch density; and derived the incidence rate ratios of the Zika virus occurrence in Colombia, South America during 2016. Negative binomial regression was used to evaluate vector-borne disease occurrence counts in relation to Population Density, Average Elevation, Per Capita Gross Domestic Product, and each of three landscape metrics. Each kilometer of border length per square kilometer of area increase in the linear density of the Cropland and Grassland classes is associated with an increase in Zika virus risk. These spatial associations inform a risk reduction approach to rural and urban morphology and land development that emphasizes simple and compact land use geometry that decreases habitat availability for mosquito vectors of Zika virus.
    Keywords:  Colombia; ZIKV; infectious disease; land use; landscape metrics; linear density; patch density; proportion abundance; vector-borne; zika virus
    DOI:  https://doi.org/10.3390/ijerph17041127
  16. Malar J. 2020 Feb 11. 19(1): 65
    Getachew D, Balkew M, Tekie H.
      BACKGROUND: Documentation of the species composition of Anopheles mosquitoes and characterization of larval breeding sites is of major importance for the implementation of larval control as part of malaria vector control interventions in Ethiopia. The aims of this study were to determine the Anopheles larval species composition, larval density, available habitat types and the effects of related environmental and physico-chemical parameters of habitats in the Ghibe River basin of southwestern Ethiopia.METHODS: Anopheles larvae were sampled from November 2014 to October 2016 on a monthly basis and 3rd and 4th instars were identified microscopically to species. The larval habitats were characterized based on habitat perimeter, water depth, intensity of light, water current, water temperature, water pH, water turbidity, distance to the nearest house, vegetation coverage, permanence of the habitat, surface debris coverage, emergent plant coverage, habitat type and substrate type.
    RESULTS: In total, 9277 larvae of Anopheles mosquitoes and 494 pupae were sampled from borrow pits, hoof prints, rain pools, pools at river edges, pools in drying river beds, rock pools, tire tracks and swamps. Anopheles larval density was highest in pools in drying river beds (35.2 larvae per dip) and lowest in swamps (2.1 larvae per dip) at Darge, but highest in rain pools (11.9 larvae per dip), borrow pits (11.2 larvae per dip) and pools at river edges (7.9 larvae per dip), and lowest in swamps (0.5 larvae per dip) at Ghibe. A total of 3485 late instar Anopheles mosquito larvae were morphologically identified. Anopheles gambiae sensu lato was the primary Anopheles mosquito found in all larval habitats except in swamps. Temperature at the time of sampling and emergent vegetation, were the most important variables for Anopheles mosquito larval density. Anopheles gambiae density was significantly associated with habitats that had smaller perimeters, were sunlit, had low vegetation cover, and a lack of emergent plants. Generally, Anopheles mosquito larval density was not significantly associated with water pH, water temperature, water turbidity, algal content, and larval habitat depth.
    CONCLUSION: Different species of Anopheles larvae were identified including An. gambiae s.l., the main malaria vector in Ethiopia. Anopheles gambiae s.l. is the most abundant species that bred in most of the larval habitat types identified in the study area. The density of this species was high in sunlit habitat, absence of emergent plants, lack of vegetation near habitat and habitats closer to human habitation. Rainfall plays a great role in determining the availability of breeding habitats. The presence of rain enable to create some of the habitat types, but alter the habitats formed at the edge of the rivers due to over flooding. Controlling the occurrence of mosquito larvae through larval source management during the dry season, targeting the pools in drying river bed and pools formed at the edge of the rivers as the water receded can be very crucial to interrupt the re-emergence of malaria vectors on the onset of rainy season.
    Keywords:  Anopheles larvae; Darge; Ghibe; Ghibe river basin; Larval habitat; Pools at river edge
    DOI:  https://doi.org/10.1186/s12936-020-3145-8
  17. J Clin Invest. 2020 Feb 11. pii: 134923. [Epub ahead of print]
    Collins KA, Wang CY, Adams M, Mitchell H, Robinson GJ, Rampton M, Elliott S, Odedra A, Khoury DS, Ballard E, Shelper TB, Lucantoni L, Avery VM, Chalon S, Möhrle JJ, McCarthy JS.
      BACKGROUND: Interventions that interrupt Plasmodium vivax transmission or eliminate dormant P. vivax liver-stage parasites will be essential for malaria elimination. Development of these interventions has been hindered by the lack of P. vivax in vitro culture and could be accelerated by a safe and reproducible clinical model in malaria-naïve individuals.METHOD: Healthy, malaria-naïve adults were enrolled in two studies to assess the safety and infectivity and transmissibility of a new P. vivax isolate. Participants (Study 1; n=2, Study 2; n=24) were inoculated with P. vivax-infected red blood cells to initiate infection, and were treated with artemether-lumefantrine (Study 1) or chloroquine (Study 2). Primary endpoints were safety and infectivity of the new isolate. In Study 2, transmission to mosquitoes was also evaluated using mosquito feeding assays, and sporozoite viability was assessed using in vitro cultured hepatocytes.
    RESULTS: Parasitaemia and gametocytemia developed in all participants and was cleared by antimalarial treatment. Adverse events were mostly mild or moderate and none were serious. Participants were infectious to Anopheles mosquitoes at peak gametocytemia 69% (11/16). Mosquito infection rates reached 97% following membrane feeding with gametocyte-enriched blood, and sporozoites developed into liver-stage schizonts in culture.
    CONCLUSION: We have demonstrated the safe, reproducible, and efficient transmission of P. vivax gametocytes from humans to mosquitoes, and have established an experimental model that will accelerate the development of interventions targeting multiple stages of the P. vivax life cycle.
    TRIAL REGISTRATION: ACTRN12614000930684 and ACTRN12616000174482.
    FUNDING: (Australian) NHMRC Program Grant: 1132975 (Study 1). Bill & Melinda Gates Foundation (OPP1111147) (Study 2).
    Keywords:  Infectious disease; Malaria; Vaccines
    DOI:  https://doi.org/10.1172/JCI134923
  18. Int J Health Geogr. 2020 Feb 11. 19(1): 3
    Lippi CA, Mao L, Stewart-Ibarra AM, Heydari N, Ayala EB, Burkett-Cadena ND, Blackburn JK, Ryan SJ.
      BACKGROUND: Vector-borne disease places a high health and economic burden in the American tropics. Comprehensive vector control programs remain the primary method of containing local outbreaks. With limited resources, many vector control operations struggle to serve all affected communities within their districts. In the coastal city of Machala, Ecuador, vector control services, such as application of larvicides and truck-mounted fogging, are delivered through two deployment facilities managed by the Ecuadorian Ministry of Health. Public health professionals in Machala face several logistical issues when delivering mosquito abatement services, namely applying limited resources in ways that will most effectively suppress vectors of malaria, dengue, and encephalitis viruses.METHODS: Using a transportation network analysis framework, we built models of service areas and optimized delivery routes based on distance costs associated with accessing neighborhoods throughout the city. Optimized routes were used to estimate the relative cost of accessing neighborhoods for mosquito control services in Machala, creating a visual tool to guide decision makers and maximize mosquito control program efficiency. Location-allocation analyses were performed to evaluate efficiency gains of moving service deployment to other available locations with respect to distance to service hub, neighborhood population, dengue incidence, and housing condition.
    RESULTS: Using this framework, we identified different locations for targeting mosquito control efforts, dependent upon management goals and specified risk factors of interest, including human population, housing condition, and reported dengue incidence. Our models indicate that neighborhoods on the periphery of Machala with the poorest housing conditions are the most costly to access. Optimal locations of facilities for deployment of control services change depending on pre-determined management priorities, increasing the population served via inexpensive routes up to 34.9%, and reducing overall cost of accessing neighborhoods up to 12.7%.
    CONCLUSIONS: Our transportation network models indicate that current locations of mosquito control facilities in Machala are not ideal for minimizing driving distances or maximizing populations served. Services may be optimized by moving vector control operations to other existing public health facilities in Machala. This work represents a first step in creating a spatial tool for planning and critically evaluating the systematic delivery of mosquito control services in Machala and elsewhere.
    Keywords:  Ecuador; GIS; Network analysis; Service delivery; Vector control
    DOI:  https://doi.org/10.1186/s12942-020-0196-6
  19. J Med Entomol. 2020 Feb 13. pii: tjaa017. [Epub ahead of print]
    Ayala AM, Vera NS, Chiappero MB, Almirón WR, Gardenal CN.
      Aedes aegypti (L.), the main vector of dengue and other arboviruses, was declared eradicated from Argentina in 1964; however, in 1987, it was detected again and nowadays it occurs in most of the country territory. To understand the transmission of vector-borne diseases, knowledge of the dispersal of vector populations is essential to evaluate the risk of pathogen transmission. We conducted a population genetic analysis of Ae. aegypti in 20 neighborhoods from Córdoba, the second largest city in Argentina, using 10 microsatellite loci. High genetic differentiation and the absence of an isolation by distance pattern was found using Weir and Cockerham's θ. Bayesian and multivariate clustering analyses showed that the studied sites included individuals with high membership coefficients (Q) in their populations, individuals with membership in another cluster, and admixed individuals. Individuals with high Q in clusters different from the population in which they were collected strongly suggests that passive transport is important in shaping the Ae. aegypti dispersal pattern in Córdoba city. Knowing the genetic structure of Ae. aegypti populations and their dispersal patterns would contribute to the implementation of vector control programs.
    Keywords:   Aedes aegypti ; Córdoba city (Argentina); microsatellites; population genetic structure
    DOI:  https://doi.org/10.1093/jme/tjaa017
  20. Acta Trop. 2020 Feb 07. pii: S0001-706X(19)31740-1. [Epub ahead of print] 105390
    Cunha MS, Faria NR, Caleiro GS, Candido DS, Hill SC, Claro IM, da Costa AC, Nogueira JS, Maeda AY, da Silva FG, de Souza RP, Spinola R, Tubaki RM, de Menezes RMT, Abade L, Mucci LF, Timenetsky MDCST, Sabino E.
      The southeastern region of Brazil has recently experienced the largest yellow fever disease outbreak in decades. Since July 2016 epizootic events were reported in São Paulo state's north region, where 787 Culicidae were captured as part of public health surveillance efforts and tested using real-time quantitative PCR. One Aedes scapularis pool collected in November 2016 in an agriculture area in Urupês city tested positive for YFV-RNA. Using a validated multiplex PCR approach we were able to recover a complete virus genome sequence from this pool. Phylogenetic analysis of the novel strain and publicly available data indicates that the belongs to the South American genotype 1 clade circulating in Sao Paulo state and is basal to the recent outbreak clade in southeast Brazil. Our findings highlight the need of additional studies, including vector competence studies, to disentangle the role of Aedes scapularis in yellow fever transmission in the Americas.
    Keywords:  Aedes; Brazil; Surveillance; Yellow fever virus
    DOI:  https://doi.org/10.1016/j.actatropica.2020.105390
  21. Malar J. 2020 Feb 13. 19(1): 70
    Coetzee M.
      BACKGROUND: In 1987, Gillies and Coetzee published a pictorial key for the morphological identification of adult female mosquitoes. Since then, several new species of anopheline mosquitoes have been described.METHODS: The 1987 key to adult female mosquitoes was used as the template for the current key.
    RESULTS: New species described in the literature over the past 32 years have been included. A list of all currently known Afrotropical species is provided. Anopheles stephensi is included for the first time as occurring on the African continent.
    CONCLUSIONS: An updated key for the morphological identification of Afrotropical anopheline species is presented.
    Keywords:  Anopheles; Identification; Key; Morphology
    DOI:  https://doi.org/10.1186/s12936-020-3144-9
  22. Infect Genet Evol. 2020 Feb 08. pii: S1567-1348(20)30069-1. [Epub ahead of print] 104237
    Lühken R, Heitmann A, Jansen S, Schmidt-Chanasit J, Börstler J, Werner D, Kampen H, Kuhn C, Pluskota B, Ferstl I, Jöst A, Becker N, Tannich E.
      The global spread of the Asian tiger mosquito Aedes albopictus is of concern, as this mosquito species constitutes an important vector of a number of emerging pathogens including dengue virus, chikungunya virus and Zika virus. Since its first appearance in Albania (1979) and Italy (1990), the species has been reported from more than twenty-five European countries. However, the dispersion process in Europe is largely unknown, as information on population genetic structure is lacking, which is relevant to understand the observed spread. In order to determine whether the ten Ae. albopictus populations detected in Germany until 2017 originate from a single introduction event or from independent importations, genetic analyses with a set of sixteen microsatellite markers were performed. The samples included specimens from three locations with potentially overwintering populations, collected in three consecutive years. The results indicate a heterogeneous population structure consisting of two clusters with significant substructuring, suggesting regular, independent introductions instead of a continuous spread across Germany originating from one or few sites. Moreover, the analyses provide further evidence for Ae. albopictus overwintering in Germany as samples from identical locations collected in three consecutive years had a relatively high genetic similarity. However, the population structure is probably influenced by local mosquito control activities. The results presented provide further evidence for regular introductions of Ae. albopictus specimens into Germany, probably leading to local establishment north of the Alps. This highlights the need for constant surveillance and control of Ae. albopictus not only in southern, but also in Central Europe.
    Keywords:  Aedes albopictus; Asian tiger mosquito; Genetic structure; Introduction; Microsatellites
    DOI:  https://doi.org/10.1016/j.meegid.2020.104237
  23. J Agric Food Chem. 2020 Feb 14.
    Yang L, Richoux GM, Norris E, Cuba IH, Jiang S, Coquerel Q, Démares F, Linthicum KJ, Bloomquist J.
      Pyrethroids are one of the most commonly used class of insecticides, and their acid and alcohol components are esterase degradation products, usually considered to be biologically inactive. In this study, it was found that several pyrethroid acids had spatial repellent activity that was greater than DEET, often more active than the parent pyrethroids, and showed little cross resistance in a pyrethroid-resistant Puerto Rico strain of Aedes aegypti mosquitoes. Further investigation revealed that the acids can synergize not only contact repellent standards, but also other pyrethroid components, as well as the parent pyrethroids themselves. Synergism by the pyrethroid acids is expressed as both increased spatial repellency and vapor toxicity, as well as human bite protection. Electrophysiological studies confirmed that pyrethroid acids (100 µM) had no effect on neuronal discharge in larval Drosophiula melanogaster CNS, were detected by electroantennography, and there was little resistance to olfactory sensing of these acids in antennae from Puerto Rico strain mosquitoes carrying kdr mutations. Thus, the data suggest that the pyrethroid acids have a different mode of action than the parent pyrethroids, unrelated to the voltage-sensitive sodium channel. The results highlight the potential of pyrethroid acids to be useful in future repellent formulations.
    DOI:  https://doi.org/10.1021/acs.jafc.9b07979
  24. Rev Inst Med Trop Sao Paulo. 2020 ;pii: S0036-46652020000100204. [Epub ahead of print]62 e10
    Monteiro FJC, Mourão FRP, Ribeiro ESD, Rêgo MODS, Frances PADC, Souto RNP, Façanha MDS, Tahmasebi R, Costa ACD.
      Aedes aegypti is associated with epidemic diseases in Brazil, such as urban yellow fever, dengue, and more recently, chikungunya and Zika viruses infections. More information about Ae. aegypti infestation is fundamental to virological surveillance in order to ensure the effectiveness of control measures in use. Thus, the present study aims to identify and compare infestation and infectivity of Ae. aegypti females in Macapa city, Amapa State (Amazon region), Brazil, between the epidemiological weeks 2017/02 and 2018/20. A total number of 303 Ae. aegypti females were collected at 21 fixed collection points, 171 at the 10 collection points in the Marabaixo neighborhood and 132 at the 11 collection points in the Central neighborhood. Among the collected samples, only two were positive for dengue virus, with a 2.08% (2/96 pools) infectivity rate for Marabaixo. The difference between the medians of Ae. aegypti females captured in Central and Marabaixo sites was not statistically significant. The findings indicate similar mosquito infestation levels between the neighborhoods, and a low-level of mosquito infectivity, although dengue virus was found only in Marabaixo. Virological surveillance of Ae. aegypti was important to identify sites of infection and determine possible routes of transmission to enable health surveillance teams to adopt preventive strategies where infected mosquitoes are present and act faster.
    DOI:  https://doi.org/10.1590/S1678-9946202062010
  25. Malar J. 2020 Feb 14. 19(1): 73
    Paaijmans KP, Huijben S.
      Long-lasting insecticidal nets, or LLINs, have significantly reduced malaria morbidity and mortality over the past two decades. The net provides a physical barrier that decreases human-mosquito contact and the impregnated insecticide kills susceptible mosquito vectors upon contact and may repel them. However, the future of LLINs is threatened as resistance to pyrethroids is now widespread, the chemical arsenal for LLINs is very limited, time from discovery of next-generation insecticides to market is long, and persistent transmission is frequently caused by vector populations avoiding contact with LLINs. Here we ask the question whether, given these challenges, insecticides should be incorporated in nets at all. We argue that developing long-lasting nets without insecticide(s) can still reduce vector populations and provide both personal and community protection, if combined with other approaches or technologies. Taking the insecticide out of the equation (i) allows for a faster response to the current pyrethroid resistance crisis, (ii) avoids an LLIN-treadmill aimed at replacing failing bed nets due to insecticide resistance, and (iii) permits the utilization of our current and future insecticidal arsenal for other vector control tools to target persistent malaria transmission.
    Keywords:  Insecticides; Malaria elimination; Resistance; Vector control
    DOI:  https://doi.org/10.1186/s12936-020-3151-x
  26. Parasitol Res. 2020 Feb 08.
    Kgoroebutswe TK, Ramatlho P, Reeder S, Makate N, Paganotti GM.
      Knowledge of vector species composition and monitoring their change over time is critical to evaluate malaria transmission and assess control interventions. This is especially important in countries such as Botswana, where malaria transmission is subjected to fluctuations due to climate variability. Another important aspect that impacts vector populations is the insecticide resistance. In order to assess species composition and the presence of mutations associated with insecticide resistance, Anopheles specimens from larval samplings and indoor pyrethrum spray sheet collections were analysed. A total of 349 Anopheles were screened by morphology and PCR as belonging to the An. gambiae complex and An. funestus group. Specimens were subsequently analysed for human blood meal and Plasmodium index. Finally, knock-down resistance polymorphisms were assessed. Anopheles arabiensis accounted for the majority of specimens collected through larval (96.7%) and pyrethrum spray sheet collection (87.4%) across all sampling sites, and this species was the only one found positive for human blood and for P. falciparum. Other Anopheles species were collected in small numbers by pyrethrum spray catches, namely An. quadriannulatus, An. longipalpis type C and An. parensis. The authors speculate on changing climate patterns and their possible impact on species composition. The kdr assay revealed that Anopheles mosquitoes were homozygous wild type for both L1014F (kdr-w) and L1014S (kdr-e) mutations. These results highlight the unique vectorial role of An. arabiensis in Botswana and indicated that even with prolonged use of pyrethroids and DDT, the mosquito population has not developed kdr mutations, despite some in vivo evidence of insecticide resistance.
    Keywords:  Anopheles arabiensis; Botswana; Insecticide resistance; Kdr; Malaria
    DOI:  https://doi.org/10.1007/s00436-020-06614-6
  27. Parasite. 2020 ;27 10
    Djamouko-Djonkam L, Nkahe DL, Kopya E, Talipouo A, Ngadjeu CS, Doumbe-Belisse P, Bamou R, Awono-Ambene P, Tchuinkam T, Wondji CS, Antonio-Nkondjio C.
      The contribution of Anopheles funestus to malaria transmission in the urban environment is still not well documented. The present study assesses the implication of An. funestus in malaria transmission in two districts, Nsam and Mendong, in the city of Yaoundé. Adult mosquitoes were collected using Centers for Disease Control and Prevention miniature light traps (CDC-LT) and human landing catches from April 2017 to March 2018 and were identified morphologically to the species level. Those belonging to the Anopheles gambiae complex and to the Anopheles funestus group were further processed by PCR to identify members of each complex/group. Anopheline mosquitoes were analysed to determine their infection status using an enzyme-linked immunosorbent assay. Bioassays were conducted with 2-5-day-old female Anopheles funestus and An. gambiae s.l. to determine their susceptibility to permethrin, deltamethrin and dichlorodiphenyltrichloroethane (DDT). Six anopheline species were collected in the peri-urban district of Mendong: Anopheles gambiae, An. coluzzii, An. funestus, An. leesoni, An. ziemanni and An. marshallii; only four out of the six were recorded in Nsam. Of the two members of the Anopheles gambiae complex collected, An. coluzzii was the most prevalent. Anopheles coluzzii was the most abundant species in Nsam, while An. funestus was the most abundant in Mendong. Both Anopheles funestus and An. gambiae s.l. were found to be infected with human Plasmodium at both sites, and both were found to be resistant to DDT, permethrin, and deltamethrin. This study confirms the participation of An. funestus in malaria transmission in Yaoundé and highlights the need to also target this species for sustainable control of malaria transmission.
    Keywords:  Anopheles funestus; Anopheles gambiae; Cameroon; Malaria; Transmission; Urban; Yaoundé
    DOI:  https://doi.org/10.1051/parasite/2020005
  28. Emerg Infect Dis. 2020 Apr 17. 26(4):
    Mina MJ, Guterman LB, Allen KE, Omer SB.
      Zika virus is transitioning to become a long-term public health challenge, and countries should remain informed of the risk for emergence. We developed a stochastic epidemiologic model to profile risk for Zika virus emergence, including trimester-specific fetal risk across time, in all 3,208 counties in the United States, including Puerto Rico. Validation against known transmission in North America demonstrated accuracy to predict epidemic dynamics and absolute case counts across scales (R2 = 0.98). We found that, although sporadic single transmission events could occur in most US counties, outbreaks will likely be restricted to the Gulf Coast region and to late spring through autumn. Seasonal fluctuations in birth rates will confer natural population-level protection against early-trimester infections. Overall, outbreak control will be more effective and efficient than prevention, and vaccination will be most effective at >70% coverage. Our county-level risk profiles should serve as a critical resource for resource allocation.
    Keywords:  United States; Zika; control; mosquitoborne diseases; risk profiling; transmission; vector-borne infections; viruses
    DOI:  https://doi.org/10.3201/eid2604.181739
  29. Am J Trop Med Hyg. 2020 Feb 10.
    Hasty JM, Felix GE, Amador M, Barrera R, Santiago GS, Nakasone L, Park SY, Okoji S, Honda E, Asuncion B, Save M, Munoz-Jordan JL, Martinez-Conde S, Medina FA, Waterman SH, Petersen LR, Johnston DI, Hemme RR.
      A dengue outbreak occurred on Hawaii Island between September 2015 and March 2016. Entomological investigations were undertaken between December 2015 and February 2016 to determine which Aedes mosquito species were responsible for the outbreak. A total of 3,259 mosquitoes were collected using a combination of CDC autocidal gravid ovitraps, Biogents BG-Sentinel traps, and hand-nets; immature mosquitoes were collected during environmental surveys. The composition of species was Aedes albopictus (58%), Aedes aegypti (25%), Wyeomyia mitchelli (7%), Aedes vexans (5%), Culex quinquefasciatus (4%), and Aedes japonicus (1%). Adult mosquitoes were analyzed by real-time reverse transcription polymerase chain reaction (PCR) for the presence of dengue virus (DENV) RNA. Of the 185 pools of female mosquitoes tested, 15 containing Ae. albopictus were positive for the presence of DENV type 1 RNA. No virus was detected in pools of the remaining species. Phylogenetic analysis showed the virus strain belonged to genotype I and was closely related to strains that were circulating in the Pacific between 2008 and 2014. This is the first report of detection of DENV in Ae. albopictus from Hawaii.
    DOI:  https://doi.org/10.4269/ajtmh.19-0732
  30. J Med Entomol. 2020 Feb 13. pii: tjaa020. [Epub ahead of print]
    Shahhosseini N, Wong G, Frederick C, Kobinger GP.
      Given current and projected changes in the climate, the composition of mosquito species is predicted to shift geographically with implications for the transmission dynamics of vector-borne pathogens. Many mosquito species are rarely collected in Canada and their history is poorly understood; thus assessing their potential role as vectors for pathogenesis is difficult. Mosquitoes were collected from four trapping sites in Quebec Province, Canada, from June to September during 2018 and 2019 using BG sentinel traps. From all morphologically identified female mosquitoes, at least one specimen was selected for identification confirmation using the DNA-barcoding technique. Sequences were subjected to alignment and a Neighbor-Joining (NJ) tree was created using Geneious software. In total, 2,752 female mosquitoes belonging to 20 species over five genera: including Aedes (Ae.), Anopheles (An.), Culex (Cx.), Culiseta (Cu.), Coquillettidia (Cq.) were collected. The predominant mosquito was found to be Ae. cinereus. The highest number of mosquito species was captured in July, followed by August, September, and then June. Five genera were characterized by a distinctive set of cytochrome oxidase I (COI) sequences that formed well-supported clusters in the NJ-tree. The presence of Ae.japonicus in Quebec provides an initial look at the distribution of mosquito species in eastern Canada, which may put Canadians at risk of a wider range of arboviruses.
    Keywords:  Canada; climate change; mosquito; pathogen; population dynamic
    DOI:  https://doi.org/10.1093/jme/tjaa020
  31. BMC Med. 2020 Feb 10. 18(1): 26
    Nguyen M, Howes RE, Lucas TCD, Battle KE, Cameron E, Gibson HS, Rozier J, Keddie S, Collins E, Arambepola R, Kang SY, Hendriks C, Nandi A, Rumisha SF, Bhatt S, Mioramalala SA, Nambinisoa MA, Rakotomanana F, Gething PW, Weiss DJ.
      BACKGROUND: Many malaria-endemic areas experience seasonal fluctuations in case incidence as Anopheles mosquito and Plasmodium parasite life cycles respond to changing environmental conditions. Identifying location-specific seasonality characteristics is useful for planning interventions. While most existing maps of malaria seasonality use fixed thresholds of rainfall, temperature, and/or vegetation indices to identify suitable transmission months, we construct a statistical modelling framework for characterising the seasonal patterns derived directly from monthly health facility data.METHODS: With data from 2669 of the 3247 health facilities in Madagascar, a spatiotemporal regression model was used to estimate seasonal patterns across the island. In the absence of catchment population estimates or the ability to aggregate to the district level, this focused on the monthly proportions of total annual cases by health facility level. The model was informed by dynamic environmental covariates known to directly influence seasonal malaria trends. To identify operationally relevant characteristics such as the transmission start months and associated uncertainty measures, an algorithm was developed and applied to model realisations. A seasonality index was used to incorporate burden information from household prevalence surveys and summarise 'how seasonal' locations are relative to their surroundings.
    RESULTS: Positive associations were detected between monthly case proportions and temporally lagged covariates of rainfall and temperature suitability. Consistent with the existing literature, model estimates indicate that while most parts of Madagascar experience peaks in malaria transmission near March-April, the eastern coast experiences an earlier peak around February. Transmission was estimated to start in southeast districts before southwest districts, suggesting that indoor residual spraying should be completed in the same order. In regions where the data suggested conflicting seasonal signals or two transmission seasons, estimates of seasonal features had larger deviations and therefore less certainty.
    CONCLUSIONS: Monthly health facility data can be used to establish seasonal patterns in malaria burden and augment the information provided by household prevalence surveys. The proposed modelling framework allows for evidence-based and cohesive inferences on location-specific seasonal characteristics. As health surveillance systems continue to improve, it is hoped that more of such data will be available to improve our understanding and planning of intervention strategies.
    Keywords:  Geostatistical model; Health facility data; Madagascar; Malaria; Seasonality
    DOI:  https://doi.org/10.1186/s12916-019-1486-3
  32. Acta Trop. 2020 Feb 10. pii: S0001-706X(19)31186-6. [Epub ahead of print] 105391
    MacCormack-Gelles B, Neto ASL, Sousa GS, do Nascimento OJ, Castro MC.
      Rapid larval surveys have been mandated in nearly every urban Brazilian municipality and promoted by the Pan American Health Organization. These surveys purport to classify arbovirus transmission risk as a basis to triage local surveillance and vector control operations, yet no previous analyses have determined relative risk associated with marginal changes in infestation at administrative and temporal scales relevant to vector control. We estimated associations between entomological indices from six larval surveys and daily incidence rates of confirmed dengue cases in Fortaleza, Brazil using models adjusted for rainfall, and indicators of spatial association. Poor correspondence between infestation and incidence indicates that these surveys may systematically mislead vector control activities and treatment strategies in Fortaleza and in similar cities throughout Latin America. The co-circulation of multiple arboviruses enhances the importance of determining the true informational value of these surveys, and of identifying complementary tools to discern local and inter-annual transmission risk.
    Keywords:  Arbovirus transmission; Household survey; Infestation index; LIRAa; Surveillance; Vector control
    DOI:  https://doi.org/10.1016/j.actatropica.2020.105391
  33. Viruses. 2020 Feb 10. pii: E196. [Epub ahead of print]12(2):
    Sow A, Nikolay B, Faye O, Cauchemez S, Cano J, Diallo M, Faye O, Sadio B, Ndiaye O, Weaver SC, Dia AT, Sall AA, Malvy D.
      In Senegal, chikungunya virus (CHIKV) is maintained in a sylvatic cycle and causes sporadic cases or small outbreaks in rural areas. However, little is known about the influence of the environment on its transmission. To address the question, 120 villages were randomly selected in the Kedougou region of southeastern Senegal. In each selected village, 10 persons by randomly selected household were sampled and tested for specific anti-CHIKV IgG antibodies by ELISA. We investigated the association of CHIKV seroprevalence with environmental variables using logistic regression analysis and the spatial correlation of village seroprevalence based on semivariogram analysis. Fifty-four percent (51%-57%) of individuals sampled during the survey tested positive for CHIKV-specific IgG. CHIKV seroprevalence was significantly higher in populations living close to forested areas (Normalized Difference Vegetation Index (NDVI), Odds Ratio (OR) = 1.90 (1.42-2.57)), and was negatively associated with population density (OR = 0.76 (0.69-0.84)). In contrast, in gold mining sites where population density was >400 people per km2, seroprevalence peaked significantly among adults (46% (27%-67%)) compared to all other individuals (20% (12%-31%)). However, traditional gold mining activities significantly modify the transmission dynamic of CHIKV, leading to a potential increase of the risk of human exposition in the region.
    Keywords:  Chikungunya; Senegal; environmental risk; gold mining; spatial autocorrelation
    DOI:  https://doi.org/10.3390/v12020196
  34. J Med Entomol. 2020 Feb 13. pii: tjaa016. [Epub ahead of print]
    Hollingsworth B, Hawkins P, Lloyd AL, Reiskind MH.
      The Asian tiger mosquito, Aedes (Stegomyia) albopictus (Skuse), is a peridomestic, container-ovipositing mosquito commonly found throughout the southeastern United States. In the United States, Ae. albopictus is typically considered a nuisance pest; however, it is capable of transmitting multiple pathogens. Ae. albopictus is an important pest species and the target of numerous mosquito control efforts in the United States. Here, we evaluate the effectiveness and spatial extent of Ae. albopictus population reduction using a bifenthrin (AI Bifen IT, 7.9%) barrier spray and larval habitat management (LHM) in a temperate, suburban setting. Sixteen pairs of adjoining neighbors were randomly assigned to treatment groups with one neighbor receiving a treatment and the other monitored for evidence of a spillover effect of the treatments. Ae. albopictus populations in both yards were monitored for 33 d, with treatments occurring on the eighth day. Barrier sprays, both alone and combined with LHM, resulted in a significant reduction in Ae. albopictus abundance posttreatment. While LHM alone did not result in a significant reduction over the entire posttreatment period, Ae. albopictus populations were observed to be in decline during this period. No treatments were observed to have any reduction in efficacy 25 d posttreatment, with treatments involving LHM having a significantly increased efficacy. Yards neighboring treated yards were also observed to have reduced population sizes posttreatment, but these differences were rarely significant. These results provide insights into the population dynamics of Ae. albopictus following two common treatments and will be useful for integrated pest management plans.
    Keywords:   Aedes albopictus ; larval habitat reduction; mosquito control; pyrethroid
    DOI:  https://doi.org/10.1093/jme/tjaa016
  35. BMC Public Health. 2020 Feb 12. 20(1): 216
    Jumbam DT, Stevenson JC, Matoba J, Grieco JP, Ahern LN, Hamainza B, Sikaala CH, Chanda-Kapata P, Cardol EI, Munachoonga P, Achee NL.
      BACKGROUND: Despite rapid upscale of insecticide-treated nets (ITNs) and indoor residual spraying (IRS), malaria remains a major source of morbidity and mortality in Zambia. Uptake and utilization of these and novel interventions are often affected by knowledge, attitudes and practices (KAP) amongst persons living in malaria-endemic areas. The aims of this study were to assess malaria KAP of primary caregivers and explore trends in relation to ITN use, IRS acceptance and mosquito density in two endemic communities in Luangwa and Nyimba districts, Zambia.METHODS: A cohort of 75 primary caregivers were assessed using a cross-sectional, forced-choice malaria KAP survey on ITN use, IRS acceptance and initial perception of a novel spatial repellent (SR) product under investigation. Entomological sampling was performed in participant homes using CDC Miniature Light Traps to relate indoor mosquito density with participant responses.
    RESULTS: Ninety-nine percent of participants cited bites of infected mosquitoes as the route of malaria transmission although other routes were also reported including drinking dirty water (64%) and eating contaminated food (63%). All caregivers agreed that malaria was a life-threatening disease with the majority of caregivers having received malaria information from health centers (86%) and community health workers (51%). Cumulatively, self-reported mosquito net use was 67%. Respondents reportedly liked the SR prototype product but improvements on color, shape and size were suggested. Overall, 398 mosquitoes were captured from light-trap collections, including 49 anophelines and 349 culicines. Insecticide treated nets use was higher in households from which at least one mosquito was captured.
    CONCLUSIONS: The current study identified misconceptions in malaria transmission among primary caregivers indicating remaining knowledge gaps in educational campaigns. Participant responses also indicated a misalignment between a low perception of IRS efficacy and high stated acceptance of IRS, which should be further examined to better understand uptake and sustainability of other vector control strategies. While ITNs were found to be used in study households, misperceptions between presence of mosquitoes and bite protection practices did exist. This study highlights the importance of knowledge attitudes and practice surveys, with integration of entomological sampling, to better guide malaria vector control product development, strategy acceptance and compliance within endemic communities.
    Keywords:  And practices (KAP); Attitudes; IRS; ITN; Knowledge; Malaria; Spatial repellents; Zambia
    DOI:  https://doi.org/10.1186/s12889-020-8235-6
  36. Trials. 2020 Feb 14. 21(1): 182
    Zinszer K, Caprara A, Lima A, Degroote S, Zahreddine M, Abreu K, Carabali M, Charland K, Dantas MA, Wellington J, Parra B, Fournet F, Bonnet E, Pérez D, Robert E, Dagenais C, Benmarhnia T, Andersson N, Ridde V.
      BACKGROUND: Dengue is increasing in its global presence with an estimated 4 billion people at-risk of infection in at least 128 countries. Despite the promising results of EcoHealth and community mobilization approaches to Aedes reduction, more evidence of their efficacy on reducing dengue risk is needed. The principal research question is to determine if interventions based upon community mobilization reduce the risk of dengue virus infection among children 3 to 9 years old compared to usual dengue control practice in Fortaleza, Brazil.METHODS: The present study will follow a pragmatic cluster randomized controlled trial (cRCT) design with randomization at the census tract level with equal allocation to the two arms. In each arm, there will be 34 clusters of 86 children between 3 to 9 years old for an expected total of 5848 children enrolled in the study, assuming a risk reduction of 29.5% based upon findings from a previous multi-site cRCT. The primary outcomes are rates of anti-dengue Immunoglobulin G (IgG) seroconversion and adult female Aedes density. The intervention is based upon a participatory health research approach, Socializing Evidence for Participatory Action (SEPA), where the research evidence is used to foster community engagement and ownership of the health issue and solution. Following allocation, intervention communities will develop and implement their own solutions that will likely include a wide variety of collective events and media approaches. Data collection activities over a period of 3 years include household visits for blood collection, household surveys, and entomological surveys; and qualitative activities including focus groups, in-depth interviews, and document analysis to evaluate the process, acceptability, fidelity, and sustainability of the intervention. Study participants will be aware of their assignment and all research staff will be blinded although the intervention assignment will likely be revealed to field staff through interaction with participants.
    DISCUSSION: The results of our study will provide evidence on community mobilization as an intervention for dengue control. We anticipate that if community mobilization is effective in Fortaleza, the results of this study will help develop evidence-based vector control programs in Brazil, and also in other countries struggling with Aedes-transmitted diseases.
    TRIAL REGISTRATION: ISRCTN66131315, registration date: 1 October 2018.
    Keywords:  Aedes mosquitos; Brazil; Cluster randomized controlled trial; Community empowerment; Community-based intervention; Dengue; Mixed methods; Vector control
    DOI:  https://doi.org/10.1186/s13063-019-3714-8
  37. Virology. 2020 Feb 02. pii: S0042-6822(20)30021-0. [Epub ahead of print]543 34-42
    Pielnaa P, Al-Saadawe M, Saro A, Dama MF, Zhou M, Huang Y, Huang J, Xia Z.
      Zika Virus (ZIKV) is a Flavivirus transmitted primarily via the bite of infected Aedes aegypti mosquitoes. Globally, 87 countries and territories have recorded autochthonous mosquito-borne transmission of ZIKV as at July 2019 and distributed across four of the six WHO Regions. Outbreaks of ZIKV infection peaked in 2016 and declined substantially throughout 2017 and 2018 in the Americas region. There is the likely risk for ZIKV to spread to more countries. There is also the potential for the re-emergence of ZIKV in all places with prior reports of the virus transmission. The current status of ZIKV transmission and spread is, however, a global health threat, and from the aforementioned, has the potential to re-emerge as an epidemic. This review summarizes the past and present spread of ZIKV outbreak-2007-2019, the genome, transmission cycle, clinical manifestations, vaccine and antiviral drug advancement.
    Keywords:  Antiviral drug development; Microcephaly; Neurological complications; Sexual transmission; Vaccine development; Zika virus (ZIKV)
    DOI:  https://doi.org/10.1016/j.virol.2020.01.015
  38. Parasit Vectors. 2020 Feb 12. 13(1): 67
    Ngassa Mbenda HG, Wang M, Guo J, Siddiqui FA, Hu Y, Yang Z, Kittichai V, Sattabongkot J, Cao Y, Jiang L, Cui L.
      BACKGROUND: The malaria elimination plan of the Greater Mekong Subregion (GMS) is jeopardized by the increasing number of Plasmodium vivax infections and emergence of parasite strains with reduced susceptibility to the frontline drug treatment chloroquine/primaquine. This study aimed to determine the evolution of the P. vivax multidrug resistance 1 (Pvmdr1) gene in P. vivax parasites isolated from the China-Myanmar border area during the major phase of elimination.METHODS: Clinical isolates were collected from 275 P. vivax patients in 2008, 2012-2013 and 2015 in the China-Myanmar border area and from 55 patients in central China. Comparison was made with parasites from three border regions of Thailand.
    RESULTS: Overall, genetic diversity of the Pvmdr1 was relatively high in all border regions, and over the seven years in the China-Myanmar border, though slight temporal fluctuation was observed. Single nucleotide polymorphisms previously implicated in reduced chloroquine sensitivity were detected. In particular, M908L approached fixation in the China-Myanmar border area. The Y976F mutation sharply decreased from 18.5% in 2008 to 1.5% in 2012-2013 and disappeared in 2015, whereas F1076L steadily increased from 33.3% in 2008 to 77.8% in 2015. While neutrality tests suggested the action of purifying selection on the pvmdr1 gene, several likelihood-based algorithms detected positive as well as purifying selections operating on specific amino acids including M908L, T958M and F1076L. Fixation and selection of the nonsynonymous mutations are differently distributed across the three border regions and central China. Comparison with the global P. vivax populations clearly indicated clustering of haplotypes according to geographic locations. It is noteworthy that the temperate-zone parasites from central China were completely separated from the parasites from other parts of the GMS.
    CONCLUSIONS: This study showed that P. vivax populations in the China-Myanmar border has experienced major changes in the Pvmdr1 residues proposed to be associated with chloroquine resistance, suggesting that drug selection may play an important role in the evolution of this gene in the parasite populations.
    Keywords:  Chloroquine resistance; Genetic diversity; Multidrug resistance 1 gene; Plasmodium vivax; Selection
    DOI:  https://doi.org/10.1186/s13071-020-3934-5