bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2021‒06‒27
nineteen papers selected by
Richard Halfpenny
Staffordshire University

  1. Virology. 2021 Jun 13. pii: S0042-6822(21)00132-X. [Epub ahead of print]561 58-64
      Pathogens are transmitted from one host to another either by vertical transmission (VT) or horizontal transmission (HT). Mosquito-borne arboviruses (arthropod-borne viruses), including several clinically important viruses such as dengue, Zika, West Nile and chikungunya viruses persist in nature by both VT and HT. VT may also serve as an essential link in the transmission cycle during adverse environmental conditions. VT rates (VTRs) vary between virus families and even among viruses within the same genus. The mechanism behind these differences in VTRs among viruses is poorly understood. For efficient VT to occur, viruses must infect the mosquito germline. Here, we show that Zika virus infects mosquito ovaries and is transmitted vertically at a low rate. The infected progeny derive from mosquitoes with infected ovaries. The prevalence of ovary infection increases after a second non-infectious blood meal following an infectious blood meal.
    Keywords:  Aedes aegypti; Arboviruses; Blood meal; Infectious blood meal; Mosquito; Vertical transmission; Zika virus
  2. PLoS One. 2021 ;16(6): e0241023
      BACKGROUND: The scale-up of indoor residual spraying and long-lasting insecticidal nets, together with other interventions have considerably reduced the malaria burden in The Gambia. This study examined the biting and resting preferences of the local insecticide-resistant vector populations few years following scale-up of anti-vector interventions.METHOD: Indoor and outdoor-resting Anopheles gambiae mosquitoes were collected between July and October 2019 from ten villages in five regions in The Gambia using pyrethrum spray collection (indoor) and prokopack aspirator from pit traps (outdoor). Polymerase chain reaction assays were performed to identify molecular species, insecticide resistance mutations, Plasmodium infection rate and host blood meal.
    RESULTS: A total of 844 mosquitoes were collected both indoors (421, 49.9%) and outdoors (423, 50.1%). Four main vector species were identified, including An. arabiensis (indoor: 15%, outdoor: 26%); An. coluzzii (indoor: 19%, outdoor: 6%), An. gambiae s.s. (indoor: 11%, outdoor: 16%), An. melas (indoor: 2%, outdoor: 0.1%) and hybrids of An. coluzzii-An. gambiae s.s (indoors: 3%, outdoors: 2%). A significant preference for outdoor resting was observed in An. arabiensis (Pearson X2 = 22.7, df = 4, P<0.001) and for indoor resting in An. coluzzii (Pearson X2 = 55.0, df = 4, P<0.001). Prevalence of the voltage-gated sodium channel (Vgsc)-1014S was significantly higher in the indoor-resting (allele freq. = 0.96, 95%CI: 0.78-1, P = 0.03) than outdoor-resting (allele freq. = 0.82, 95%CI: 0.76-0.87) An. arabiensis population. For An. coluzzii, the prevalence of most mutation markers was higher in the outdoor (allele freq. = 0.92, 95%CI: 0.81-0.98) than indoor-resting (allele freq. = 0.78, 95%CI: 0.56-0.86) mosquitoes. However, in An. gambiae s.s., the prevalence of Vgsc-1014F, Vgsc-1575Y and GSTe2-114T was high (allele freq. = 0.96-1), but did not vary by resting location. The overall sporozoite positivity rate was 1.3% (95% CI: 0.5-2%) in mosquito populations. Indoor-resting An. coluzzii had mainly fed on human blood while indoor-resting An. arabiensis fed on animal blood.
    CONCLUSION: In this study, high levels of resistance mutations were observed that could be influencing the mosquito populations to rest indoors or outdoors. The prevalent animal-biting behaviour demonstrated in the mosquito populations suggest that larval source management could be an intervention to complement vector control in this setting.
  3. Malar J. 2021 Jun 22. 20(1): 273
      BACKGROUND: The efficacy of insecticide-treated nets (ITNs) containing the insect growth regulator pyriproxyfen (PPF) and pyrethroid insecticides (PPF-ITNs) is being assessed in clinical trials to determine whether they provide greater protection from malaria than standard pyrethroid-treated ITNs in areas where mosquitoes are resistant to pyrethroids. Understanding the entomological mode of action of this new ITN class will aide interpretation of the results from these trials.METHODS: Anopheles gambiae sensu lato (s.l.) mosquitoes from a susceptible laboratory strain were exposed to PPF-treated netting 24 h, 6 h, and immediately prior to, or 24 h post blood feeding, and the impact on fecundity, fertility and longevity recorded. Pyrethroid-resistant populations were exposed to nets containing permethrin and PPF (PPF-ITNs) in cone bioassays and daily mortality recorded. Mosquitoes were also collected from inside houses pre- and post-distribution of PPF-ITNs in a clinical trial conduced in Burkina Faso; female An. gambiae s.l. were then assessed for fecundity and fertility.
    RESULTS: PPF exposure reduced the median adult lifespan of insecticide-susceptible mosquitoes by 4 to 5 days in all exposure times (p < 0.05) other than 6 h pre-blood meal and resulted in almost complete lifelong sterilization. The longevity of pyrethroid-resistant mosquitoes was also reduced by at least 5 days after exposure to PPF-ITNs compared to untreated nets, but was unaffected by exposure to standard pyrethroid only ITNs. A total of 386 blood-fed or gravid An. gambiae s.l. females were collected from five villages between 1 and 12 months before distribution of PPF-ITNs. Of these mosquitoes, 75% laid eggs and the remaining 25% appeared to have normal ovaries upon dissection. In contrast, only 8.6% of the 631 blood-fed or gravid An. gambiae s.l. collected post PPF-ITN distribution successfully oviposited; 276 (43.7%) did not oviposit but had apparently normal ovaries upon dissection, and 301 (47.7%) did not oviposit and had abnormal eggs upon dissection. Egg numbers were also significantly lower (average of 138/female prior distribution vs 85 post distribution, p < 0.05).
    CONCLUSION: Exposure to a mixture of PPF and pyrethroids on netting shortens the lifespan of mosquitoes and reduces reproductive output. Sterilization of vectors lasted at least one year under operational conditions. These findings suggest a longer effective lifespan of PPF-pyrethroid nets than reported previously.
    Keywords:  Anopheles gambiae; Insecticide-treated nets (ITNs); Juvenile hormone (JH); Olyset Duo®; Pyrethroid-resistance; Pyriproxyfen (PPF)
  4. Transbound Emerg Dis. 2021 Jun 24.
      Increased globalization and international transportation have resulted in the inadvertent introduction of exotic mosquitoes and new mosquito-borne diseases. International airports are among the possible points of entry for mosquitoes and their pathogens. We established a mosquito and mosquito-borne diseases monitoring program at the largest international airport in Austria and report the results for the first two years, 2018 and 2019. This included weekly monitoring and sampling of adult mosquitoes, and screening them for the presence of viral nucleic acids by standard molecular diagnostic techniques. Additionally, we surveyed the avian community at the airport, as birds are potentially amplifying hosts. In 2018, West Nile virus (WNV) was detected in 14 pools and Usutu virus (USUV) was detected in another 14 pools (minimum infection rate of 6.8 for each virus). Of these 28 pools, 26 consisted of female Culex pipiens/torrentium, and two contained male Culex sp. mosquitoes. Culex pipiens/torrentium mosquitoes were the most frequently captured mosquito species at the airport. The detected WNV strains belonged to five sub-clusters within the sub-lineage 2d-1, and all detected USUV strains were grouped to at least seven sub-clusters among the cluster Europe 2; all strains were previously shown to be endemic in Austria. In 2019, all mosquito pools were negative for any viral nucleic acids tested. Our study suggests that airports may serve as foci of arbovirus activity, particularly during epidemic years, and should be considered when designing mosquito control and arbovirus monitoring programs. This article is protected by copyright. All rights reserved.
    Keywords:  Austria; Culex pipiens - mosquito-borne diseases - Usutu virus - West Nile virus - virus monitoring - airport
  5. Acta Trop. 2021 Jun 16. pii: S0001-706X(21)00193-5. [Epub ahead of print] 106014
      The growth of resistance in vector mosquitoes to insecticides, especially the organophosphate Temephos can facilitate the transmission of various disease agents worldwide. Consequently, it arises a challenge to public health agencies, which is the urgency use of other possibilities as botanical insecticides. Such insecticides have specific properties against insects due to the plant's ability to synthesize products derived from its secondary metabolism. The diversity and complexity of active compounds of botanical insecticides can help reduce the selection of resistant individuals and consequently not change susceptibility. To corroborate this hypothesis, the aim of this study was to compare two populations of Aedes aegypti treated with Temephos and Copaifera oleoresin. Thus, Ae. aegypti larvae were exposed from (F1) up to tenth generation (F10) with sublethal doses (±LC25) of these products (Copaifera oleoresin: 40 mg/L and Temephos: 0.0030 mg/L). The triplicates and control groups were monitored every 48 hours and the surviving larvae were separated until the emergence of the adults. Each new population were then subjected to a series of concentrations (LC50 and LC95) of Temephos and Copaifera oleoresin to calculate the Resistance Ratio (RR) of each exposed generation. The population of Ae. aegypti exposed to Temephos had an increase in RR from 05 (considered low) to 13 (considered high). Those population exposed to Copaifera oleoresin, had no increasing in RR and continued susceptible to the oil in all generations. There was a significant difference in mortality between the generations exposed to the two products. The results presented here show that the change in the susceptibility status of Ae. aegypti population to Temephos was already expected. So, we believe that this work will be of great contribution to research related to mosquito control with plant products, and resistance to chemical insecticides.
    Keywords:  Botanical insecticides; Mosquito control; Oleoresin; Resistance; Susceptibility
  6. Ethiop J Health Sci. 2021 Mar;31(2): 247-256
      Background: Management of malaria transmission relies heavily on vector control. Implementation and sustenance of effective control measures require regular monitoring of malaria vector occurrences, species abundance and distribution. The study assessed mosquito larval species composition, distribution and productivity in Kakamega County, western Kenya.Methods: A cross-sectional survey of Anopheline larvae was conducted in various aquatic habitats and land use types in Kakamega County, highlands of western Kenya between the month of March and June 2019.
    Results: One thousand, five hundred and seventy six aquatic habitats were sampled in various land use types. The mean densities of An. gambiae s.l (46.2), An. funestus (5.3), An. coustani (1.7), An. implexus (0.13) and An. squamosus (2.0) were observed in fish ponds, burrow pits, drainage ditches, and tire tracks, respectively. High mean densities of An. gambiae s.l was reported in farmland (20.4) while high mean abundance of An. funestus s.l (8.2) and An. coustani s.l (4.0) were observed in artificial forests.
    Conclusion: The study revealed that the productivity of anopheles larvae varied across various habitat types and land use types. Therefore, treatment of potential breeding sites should be considered as an additional strategy for malaria vector control in Kakamega County, western Kenya.
    Keywords:  Anopheles larvae; aquatic habitat; land use type; malaria transmission; malaria vector
  7. PLoS Negl Trop Dis. 2021 Jun 21. 15(6): e0009497
      Japanese encephalitis (JE) is the major cause of viral encephalitis (VE) in most Asian-Pacific countries. In Vietnam, there is no nationwide surveillance system for JE due to lack of medical facilities and diagnoses. Culex tritaeniorhynchus, Culex vishnui, and Culex quinquefasciatus have been identified as the major JE vectors in Vietnam. The main objective of this study was to forecast a risk map of Culex mosquitoes in Hanoi, which is one of the most densely populated cities in Vietnam. A total of 10,775 female adult Culex mosquitoes were collected from 513 trapping locations. We collected temperature and precipitation information during the study period and its preceding month. In addition, the other predictor variables (e.g., normalized difference vegetation index [NDVI], land use/land cover and human population density), were collected for our analysis. The final model selected for estimating the Culex mosquito abundance included centered rainfall, quadratic term rainfall, rice cover ratio, forest cover ratio, and human population density variables. The estimated spatial distribution of Culex mosquito abundance ranged from 0 to more than 200 mosquitoes per 900m2. Our model estimated that 87% of the Hanoi area had an abundance of mosquitoes from 0 to 50, whereas approximately 1.2% of the area showed more than 150 mosquitoes, which was mostly in the rural/peri-urban districts. Our findings provide better insight into understanding the spatial distribution of Culex mosquitoes and its associated environmental risk factors. Such information can assist local clinicians and public health policymakers to identify potential areas of risk for JE virus. Risk maps can be an efficient way of raising public awareness about the virus and further preventive measures need to be considered in order to prevent outbreaks and onwards transmission of JE virus.
  8. Vector Borne Zoonotic Dis. 2021 Jun 22.
      Culex pipiens sensu lato has been documented as West Nile virus (WNV) vector in southeastern Romania. Bucharest, the densely populated capital city of Romania, and the surrounding Ilfov county are WNV hotspots. In this area, the morphologically indistinguishable biotypes of Cx. pipiens, namely pipiens and molestus, are usually differentiated by their behavioral and physiological traits. Their involvement in WNV transmission, as suggested by entomological investigations, was not previously documented for each biotype. We used a Real-Time PCR assay based on CQ11 microsatellite to identify the Cx. pipiens biotypes and their hybrids collected in various habitats in the Bucharest metropolitan area. A sympatric distribution of both biotypes was observed, with a preference of green areas for pipiens, and human settings and animal farmlands for molestus. In the latter habitats, pipiens and molestus were found in mixed aboveground populations. A low number of hybrids was found suggesting existence of reproductive isolation. In subway tunnels molestus was dominant with a higher number of hybrids recorded than aboveground. Blood-engorged mosquitoes were identified to biotype and the blood meal source identified by DNA barcoding. Overall, Cx. pipiens s.l. fed mainly on birds, commonly on house sparrows, collared doves, and blackbirds, which are potential WNV-amplifying hosts. The preference for avian hosts was expressed strongest by pipiens biotype, while molestus was substantially less specific, feeding on avian and mammal hosts with similar frequency, with humans representing 20% of the hosts. Hybrids had a host choice closer to that of molestus. These findings highlight the role of pipiens biotype as enzootic/epizootic vector, and specifically show molestus as the bridge vector for WNV. The pipiens and molestus biotypes show important differences in habitat preferences, including oviposition; these findings demonstrate that targeted mosquito control to limit WNV transmission may be possible.
    Keywords:  Culex pipiens s.l.; biotype identification; blood meal analysis; hybrids; sympatric distribution
  9. Lancet Infect Dis. 2021 Jun 16. pii: S1473-3099(21)00072-4. [Epub ahead of print]
      BACKGROUND: Symptomatic malaria cases reflect only a small proportion of all Plasmodium spp infections. Many infected individuals are asymptomatic, and persistent asymptomatic Plasmodium falciparum infections are common in endemic settings. We aimed to quantify the contribution of symptomatic and asymptomatic infections to P falciparum transmission in Tororo, Uganda.METHODS: We did a longitudinal, observational cohort study in Tororo district, Uganda. We recruited participants of all ages from randomly selected households within this district. Participants were eligible if the selected household had no more than nine permanent residents and at least two members younger than 10 years, and the household was their primary residence, and they agreed to come to the study clinic for any fever episode and avoid antimalarial medications outside the study. Participants were followed-up by continuous passive surveillance for the incidence of symptomatic infections; routine assessments (ie, standardised clinical evaluation and blood samples) were done at baseline and at routine visits every 4 weeks for 2 years. P falciparum parasite density, gametocyte density, and genetic composition were determined molecularly using quantitative PCR (qPCR), quantitative reverse transcriptase PCR (qRT-PCR), and amplicon deep sequencing, respectively. Membrane feeding assays were also done to assess infectivity to mosquitoes. The contribution of different populations to the infectious reservoir was estimated for symptomatic infections, asymptomatic but microscopically detected infections, and asymptomatic but qPCR-detected infections; and for age groups younger than 5 years, 5-15 years, and 16 years or older.
    FINDINGS: Between Oct 4, 2017, and Oct 31, 2019, 531 individuals were enrolled from 80 randomly selected households and were followed-up for 2 years. At baseline, P falciparum was detected in 28 (5·3%) of 531 participants by microscopy and an additional 64 (12·1%) by qPCR and declined thereafter. In 538 mosquito feeding experiments on 107 individuals, 446 (1·2%) of 37 404 mosquitoes became infected, with mosquito infection rates being strongly associated with gametocyte densities (β=2·11, 95% CI 1·62-2·67; p<0·0001). Considering both transmissibility of infections and their relative frequency, the estimated human infectious reservoir consisted primarily of asymptomatic microscopy-detected infections (83·8%), followed by asymptomatic submicroscopic infections (15·6%), and symptomatic infections (0·6%). Children aged 5-15 years accounted for more than half of the infectious reservoir (58·7%); individuals younger than 5 years (25·8%) and those 16 years or older (15·6%) contributed less. Samples from four children contribued to 279 (62·6%) of 446 infected mosquitoes after multiple mosquito-feeding assays.
    INTERPRETATION: Individuals with asymptomatic infections were important drivers of malaria transmission. School-aged children contributed to more than half of all mosquito infections, with a small minority of asymptomatic children being highly infectious. Demographically targeted interventions, aimed at school-aged children, could further reduce transmission in areas under effective vector control.
    FUNDING: US National Institutes of Health, Bill & Melinda Gates Foundation, and the European Research Council.
  10. Parasit Vectors. 2021 Jun 22. 14(1): 331
      BACKGROUND: Although American crows are a key indicator species for West Nile virus (WNV) and mount among the highest viremias reported for any host, the importance of crows in the WNV transmission cycle has been called into question because of their consistent underrepresentation in studies of Culex blood meal sources. Here, we test the hypothesis that this apparent underrepresentation could be due, in part, to underrepresentation of crow nesting habitat from mosquito sampling designs. Specifically, we examine how the likelihood of a crow blood meal changes with distance to and timing of active crow nests in a Davis, California, population.METHODS: Sixty artificial mosquito resting sites were deployed from May to September 2014 in varying proximity to known crow nesting sites, and Culex blood meal hosts were identified by DNA barcoding. Genotypes from crow blood meals and local crows (72 nestlings from 30 broods and 389 local breeders and helpers) were used to match mosquito blood meals to specific local crows.
    RESULTS: Among the 297 identified Culex blood meals, 20 (6.7%) were attributable to crows. The mean percentage of blood meals of crow origin was 19% in the nesting period (1 May-18 June 2014), but 0% in the weeks after fledging (19 June-1 September 2014), and the likelihood of a crow blood meal increased with proximity to an active nest: the odds that crows hosted a Culex blood meal were 38.07 times greater within 10 m of an active nest than > 10 m from an active nest. Nine of ten crow blood meals that could be matched to a genotype of a specific crow belonged to either nestlings in these nests or their mothers. Six of the seven genotypes that could not be attributed to sampled birds belonged to females, a sex bias likely due to mosquitoes targeting incubating or brooding females.
    CONCLUSION: Data herein indicate that breeding crows serve as hosts for Culex in the initial stages of the WNV spring enzootic cycle. Given their high viremia, infected crows could thereby contribute to the re-initiation and early amplification of the virus, increasing its availability as mosquitoes shift to other moderately competent later-breeding avian hosts.
    Keywords:  American crow; Blood meal identification; Corvus brachyrhynchos; Culex pipiens; Culex tarsalis; Microsatellite analysis; Molecular sexing; West Nile virus
  11. J Gen Virol. 2021 Jun;102(6):
      Mosquito-transmitted arboviruses constitute a large proportion of emerging infectious diseases that are both a public health problem and a threat to animal populations. Many such viruses were identified in East Africa, a region where they remain important and from where new arboviruses may emerge. We set out to describe and review the relevant mosquito-borne viruses that have been identified specifically in Uganda. We focused on the discovery, burden, mode of transmission, animal hosts and clinical manifestation of those previously involved in disease outbreaks. A search for mosquito-borne arboviruses detected in Uganda was conducted using search terms 'Arboviruses in Uganda' and 'Mosquitoes and Viruses in Uganda' in PubMed and Google Scholar in 2020. Twenty-four mosquito-borne viruses from different animal hosts, humans and mosquitoes were documented. The majority of these were from family Peribunyaviridae, followed by Flaviviridae, Togaviridae, Phenuiviridae and only one each from family Rhabdoviridae and Reoviridae. Sixteen (66.7 %) of the viruses were associated with febrile illnesses. Ten (41.7 %) of them were first described locally in Uganda. Six of these are a public threat as they have been previously associated with disease outbreaks either within or outside Uganda. Historically, there is a high burden and endemicity of arboviruses in Uganda. Given the many diverse mosquito species known in the country, there is also a likelihood of many undescribed mosquito-borne viruses. New generation diagnostic platforms have great potential to identify new viruses. Indeed, four novel viruses, two of which were from humans (Ntwetwe and Nyangole viruses) and two from mosquitoes (Kibale and Mburo viruses) including the 2010 yellow fever virus (YFV) outbreak were identified in the last decade using next generation sequencing. Given the unbiased approach of detection of viruses by this technology, its use will undoubtedly be critically important in the characterization of mosquito viromes which in turn will inform other diagnostic efforts.
    Keywords:  Uganda; history; mosquito-borne arboviruses; outbreaks
  12. Sci Total Environ. 2021 Jun 10. pii: S0048-9697(21)03477-X. [Epub ahead of print]792 148406
      BACKGROUND: Dengue is an endemic vector-borne disease influenced by environmental factors such as landscape and climate. Previous studies separately assessed the effects of landscape and climate factors on mosquito occurrence and dengue incidence. However, both factors concurrently coexist in time and space and can interact, affecting mosquito development and dengue disease transmission. For example, eggs laid in a suitable environment can hatch after being submerged in rain water. It has been difficult for conventional statistical modeling approaches to demonstrate these combined influences due to mathematical constraints.OBJECTIVES: To investigate the combined influences of landscape and climate factors on mosquito occurrence and dengue incidence.
    METHODS: Entomological, epidemiological, and landscape data from the rainy season (July-December) were obtained from respective government agencies in Metropolitan Manila, Philippines, from 2012 to 2014. Temperature, precipitation and vegetation data were obtained through remote sensing. A random forest algorithm was used to select the landscape and climate variables. Afterward, using the identified key variables, a model-based (MOB) recursive partitioning was implemented to test the combined influences of landscape and climate factors on ovitrap index (vector mosquito occurrence) and dengue incidence.
    RESULTS: The MOB recursive partitioning for ovitrap index indicated a high sensitivity of vector mosquito occurrence on environmental conditions generated by a combination of high residential density areas with low precipitation. Moreover, the MOB recursive partitioning indicated high sensitivity of dengue incidence to the effects of precipitation in areas with high proportions of residential density and commercial areas.
    CONCLUSIONS: Dengue dynamics are not solely influenced by individual effects of either climate or landscape, but rather by their synergistic or combined effects. The presented findings have the potential to target vector surveillance in areas identified as suitable for mosquito occurrence under specific climatic conditions and may be relevant as part of urban planning strategies to control dengue.
    Keywords:  Combined influences; Dengue; Environmental factors; Random forest; Recursive partitioning
  13. PLoS Pathog. 2021 Jun;17(6): e1009637
      The Dilution Effect Hypothesis (DEH) argues that greater biodiversity lowers the risk of disease and reduces the rates of pathogen transmission since more diverse communities harbour fewer competent hosts for any given pathogen, thereby reducing host exposure to the pathogen. DEH is expected to operate most intensely in vector-borne pathogens and when species-rich communities are not associated with increased host density. Overall, dilution will occur if greater species diversity leads to a lower contact rate between infected vectors and susceptible hosts, and between infected hosts and susceptible vectors. Field-based tests simultaneously analysing the prevalence of several multi-host pathogens in relation to host and vector diversity are required to validate DEH. We tested the relationship between the prevalence in house sparrows (Passer domesticus) of four vector-borne pathogens-three avian haemosporidians (including the avian malaria parasite Plasmodium and the malaria-like parasites Haemoproteus and Leucocytozoon) and West Nile virus (WNV)-and vertebrate diversity. Birds were sampled at 45 localities in SW Spain for which extensive data on vector (mosquitoes) and vertebrate communities exist. Vertebrate censuses were conducted to quantify avian and mammal density, species richness and evenness. Contrary to the predictions of DEH, WNV seroprevalence and haemosporidian prevalence were not negatively associated with either vertebrate species richness or evenness. Indeed, the opposite pattern was found, with positive relationships between avian species richness and WNV seroprevalence, and Leucocytozoon prevalence being detected. When vector (mosquito) richness and evenness were incorporated into the models, all the previous associations between WNV prevalence and the vertebrate community variables remained unchanged. No significant association was found for Plasmodium prevalence and vertebrate community variables in any of the models tested. Despite the studied system having several characteristics that should favour the dilution effect (i.e., vector-borne pathogens, an area where vector and host densities are unrelated, and where host richness is not associated with an increase in host density), none of the relationships between host species diversity and species richness, and pathogen prevalence supported DEH and, in fact, amplification was found for three of the four pathogens tested. Consequently, the range of pathogens and communities studied needs to be broadened if we are to understand the ecological factors that favour dilution and how often these conditions occur in nature.
  14. PLoS One. 2021 ;16(6): e0252690
      In areas of low and unstable transmission, malaria cases occur in populations with lower access to malaria services and interventions, and in groups with specific malaria risk exposures often away from the household. In support of the Namibian National Vector Borne Disease Program's drive to better target interventions based upon risk, we implemented a health facility-based case control study aimed to identify risk factors for symptomatic malaria in Zambezi Region, northern Namibia. A total of 770 febrile individuals reporting to 6 health facilities and testing positive by rapid diagnostic test (RDT) between February 2015 and April 2016 were recruited as cases; 641 febrile individuals testing negative by RDT at the same health facilities through June 2016 were recruited as controls. Data on socio-demographics, housing construction, overnight travel, use of malaria prevention and outdoor behaviors at night were collected through interview and recorded on a tablet-based questionnaire. Remotely-sensed environmental data were extracted for geo-located village residence locations. Multivariable logistic regression was conducted to identify risk factors and latent class analyses (LCA) used to identify and characterize high-risk subgroups. The majority of participants (87% of cases and 69% of controls) were recruited during the 2016 transmission season, an outbreak year in Southern Africa. After adjustment, cases were more likely to be cattle herders (Adjusted Odds Ratio (aOR): 4.46 95%CI 1.05-18.96), members of the police or other security personnel (aOR: 4.60 95%CI: 1.16-18.16), and pensioners/unemployed persons (aOR: 2.25 95%CI 1.24-4.08), compared to agricultural workers (most common category). Children (aOR 2.28 95%CI 1.13-4.59) and self-identified students were at higher risk of malaria (aOR: 4.32 95%CI 2.31-8.10). Other actionable risk factors for malaria included housing and behavioral characteristics, including traditional home construction and sleeping in an open structure (versus modern structure: aOR: 2.01 95%CI 1.45-2.79 and aOR: 4.76 95%CI: 2.14-10.57); cross border travel in the prior 30 days (aOR: 10.55 95%CI 2.94-37.84); and outdoor agricultural work at night (aOR: 2.09 95%CI 1.12-3.87). Malaria preventive activities were all protective and included personal use of an insecticide treated net (ITN) (aOR: 0.61 95%CI 0.42-0.87), adequate household ITN coverage (aOR: 0.63 95%CI 0.42-0.94), and household indoor residual spraying (IRS) in the past year (versus never sprayed: (aOR: 0.63 95%CI 0.44-0.90). A number of environmental factors were associated with increased risk of malaria, including lower temperatures, higher rainfall and increased vegetation for the 30 days prior to diagnosis and residing more than 5 minutes from a health facility. LCA identified six classes of cases, with class membership strongly correlated with occupation, age and select behavioral risk factors. Use of ITNs and IRS coverage was similarly low across classes. For malaria elimination these high-risk groups will need targeted and tailored intervention strategies, for example, by implementing alternative delivery methods of interventions through schools and worksites, as well as the use of specific interventions that address outdoor transmission.
  15. Biol Open. 2021 Jun 22. pii: bio.058855. [Epub ahead of print]
      Vector-borne pathogens cause many human infectious diseases and are responsible for high mortality and morbidity throughout the world. They can also cause livestock epidemics with dramatic social and economic consequences. Due to its high costs, vector-borne disease surveillance is often limited to current threats, and the investigation of emerging pathogens typically occurs after the reports of clinical cases. Here, we use high-throughput sequencing to detect and identify a wide range of parasites and viruses carried by mosquitoes from Cambodia, Guinea, Mali and Maryland. We apply this approach to individual Anopheles mosquitoes as well as pools of mosquitoes captured in traps; and compare the outcomes of this assay when applied to DNA or RNA. We identified known human and animal pathogens and mosquito parasites belonging to a wide range of taxa, as well as novel DNA sequences from previously uncharacterized organisms. Our results also revealed that analysis of the content of an entire trap could be an efficient approach to monitor and identify rare vector-borne pathogens in large surveillance studies. Overall, we describe a high-throughput and easy-to-customize assay to screen for a wide-range of pathogens and efficiently complement current vector-borne disease surveillance approaches.
    Keywords:  Arbovirus; Emerging pathogens; Eukaryotic parasites; Surveillance; Vector-borne pathogens; Zoonosis
  16. Front Microbiol. 2021 ;12 689979
      Chikungunya virus (CHIKV) is a vector (mosquito)-transmitted alphavirus (family Togaviridae). CHIKV can cause fever and febrile illness associated with severe arthralgia and rash. Genotypic and phylogenetic analysis are important to understand the spread of CHIKV during epidemics and the diversity of circulating strains for the prediction of effective control measures. Molecular epidemiologic analysis of CHIKV is necessary to understand the complex interaction of vectors, hosts and environment that influences the genotypic evolution of epidemic strains. In this study, different works published during 1950s to 2020 concerning CHIKV evolution, epidemiology, vectors, phylogeny, and clinical outcomes were analyzed. Outbreaks of CHIKV have been reported from Bangladesh, Bhutan, India, Pakistan, Sri Lanka, Nepal, and Maldives in South Asia during 2007-2020. Three lineages- Asian, East/Central/South African (ECSA), and Indian Ocean Lineage (IOL) are circulating in South Asia. Lineage, ECSA and IOL became predominant over Asian lineage in South Asian countries during 2011-2020 epidemics. Further, the mutant E1-A226V is circulating in abundance with Aedes albopictus in India, Bangladesh, Nepal, and Bhutan. CHIKV is underestimated as clinical symptoms of CHIKV infection merges with the symptoms of dengue fever in South Asia. Failure to inhibit vector mediated transmission and predict epidemics of CHIKV increase the risk of larger global epidemics in future. To understand geographical spread of CHIKV, most of the studies focused on CHIKV outbreak, biology, pathogenesis, infection, transmission, and treatment. This updated study will reveal the collective epidemiology, evolution and phylogenies of CHIKV, supporting the necessity to investigate the circulating strains and vectors in South Asia.
    Keywords:  South Asia; chikungunya virus; epidemiology; evolution; phylogeny
  17. Braz J Biol. 2021 ;pii: S1519-69842022000100231. [Epub ahead of print]82 e241338
      Mosquito-borne diseases result in the loss of life and economy, primarily in subtropical and tropical countries, and the emerging resistance to insecticides is increasing this threat. Botanical insecticides are promising substitutes for synthetic insecticides. This study evaluated the larvicidal and growth index of Culex pipiens of four solvent extracts of Terminalia chebula, Aloe perryi, and Peganum harmala against Cx. pipiens. None of the 12 extracts exhibited larvicidal potential against third instars except the ethyl acetate extract of P. harmala. After 24 h of exposure, the LC50 value was 314.88 ppm, and the LC90 value was 464.19 ppm. At 320 ppm, the hatchability was 25.83%, and it resulted in 100% mortality. In addition, the eggs treated with the EtOAc extract of P. Harmala exhibited a long larval period compared with the control. The larval period continued for 12 days, and the pupal period took three days in the treatment groups. The growth index data also exhibited a decrease (0.00-7.53) in the treated groups compare with 8.5 in the control. The transformation of eggs into adults decreased with increasing concentrations. This paper is the first report on the development and growth index of Cx. pipiens potential using P. harmala seeds.
  18. BMC Public Health. 2021 Jun 23. 21(1): 1199
      BACKGROUND: Zika virus (ZIKV) infection caused outbreak in Brazil, in 2015 and 2016. Disorganized urban growth, facilitates the concentration of numerous susceptible and infected individuals. It is useful to understand the mechanisms that can favor the increase in ZIKV incidence, such as areas with wide socioeconomic and environmental diversity. Therefore, the study analyzed the spatial distribution of ZIKV in the city of Rio de Janeiro, Brazil, in 2015 and 2016, and associations between the incidence per 1000 inhabitants and socio-environmental factors.METHODS: The census tracts were used as the analytical units reported ZIKV cases among the city's inhabitants. Local Empirical Bayesian method was used to control the incidence rates' instability effect. The spatial autocorrelation was verified with Moran's Index and local indicators of spatial association (LISA). Spearman correlation matrix was used to indicate possible collinearity. The Ordinary Least Squares (OLS), Spatial Lag Model (SAR), and Spatial Error Model (CAR) were used to analyze the relationship between ZIKV and socio-environmental factors.
    RESULTS: The SAR model exhibited the best parameters: R2 = 0.44, Log-likelihood = - 7482, Akaike Information Criterion (AIC) = 14,980. In this model, mean income between 1 and 2 minimum wages was possible risk factors for Zika occurrence in the localities. Household conditions related to adequate water supply and the existence of public sewage disposal were associated with lower ZIKV cumulative incidence, suggesting possible protective factors against the occurrence of ZIKV in the localities. The presence of the Family Health Strategy in the census tracts was positively associated with the ZIKV cumulative incidence. However, the results show that mean income less than 1 minimum wage were negatively associated with higher ZIKV cumulative incidence.
    CONCLUSION: The results demonstrate the importance of socio-environmental variables in the dynamics of ZIKV transmission and the relevance for the development of control strategies.
    Keywords:  Arbovirus; Socio-environmental; Spatial analysis; Theoretical model; Zika virus
  19. Trop Biomed. 2021 Jun 01. 38(2): 196-204
      Susceptibility status of Aedes albopictus (Skuse) sampled from residential areas in Interior, Sandakan and Tawau divisions of Sabah, Malaysia, was evaluated based on the WHOrecommended doses of organochlorine and organophosphate larvicides. To determine susceptibility status, larval bioassays were carried out and post 24-hour mortalities based on WHO resistance classifications were adopted. The results demonstrated that Ae. albopictus larvae were resistant toward 5 out of the 8 larvicides tested. Larvae from all populations were resistant against bromophos, fenitrothion, malathion, temephos and dichlorodiphenyltrichloroethane (DDT), with mortalities ranging from 0.00 to 89.33%. Dieldrin, on the other hand, could induce 100.00% mortalities in all populations, followed by fenthion and chlorpyrifos, with mortalities ranging from 97.33 to 100.00% and 81.33 to 100.00% respectively. Despite most populations exhibiting similitude in their resistance status, larvae from Sandakan exhibited the highest resistance level whereas the lowest level was observed in Keningau. In view of the inadequacy of some larvicides in controlling Ae. albopictus in this study, integrated management such as insecticide rotation or combination of interventions is warranted.