bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒12‒13
twenty-one papers selected by
Richard Halfpenny
Staffordshire University

  1. Malar J. 2020 Dec 09. 19(1): 454
    Kouassi BL, Edi C, Tia E, Konan LY, Akré MA, Koffi AA, Ouattara AF, Tanoh AM, Zinzindohoue P, Kouadio B, Andre M, Irish SR, Armistead J, Dengela D, Cissé NG, Flatley C, Chabi J.
      BACKGROUND: Pyrethroid-treated mosquito nets are currently the mainstay of vector control in Côte d'Ivoire. However, resistance to pyrethroids has been reported across the country, limiting options for insecticide resistance management due to the paucity of alternative insecticides. Two types of insecticide-treated nets (ITNs), ITNs with pyrethroids and the synergist piperonyl butoxide (PBO), and Interceptor®G2 nets, a net treated with a combination of chlorfenapyr and alpha-cypermethrin, are believed to help in the control of pyrethroid-resistant mosquitoes.METHODS: The susceptibility of Anopheles gambiae sensu lato (s.l.) to pyrethroid insecticides with and without pre-exposure to PBO as well as to chlorfenapyr was investigated in fifteen sites across the country. Susceptibility tests were conducted on 2- to 4-day old adult female An. gambiae s.l. reared from larval collections. The resistance status, intensity, and effects of PBO on mortality after exposure to different concentrations of deltamethrin, permethrin and alpha-cypermethrin were determined using WHO susceptibility test kits. In the absence of a WHO-recommended standard protocol for chlorfenapyr, two interim doses (100 and 200 µg/bottle) were used to test the susceptibility of mosquitoes using the CDC bottle assay method.
    RESULTS: Pre-exposure to PBO did not result in full restoration of susceptibility to any of the three pyrethroids for the An. gambiae s.l. populations from any of the sites surveyed. However, PBO pre-exposure did increase mortality for all three pyrethroids, particularly deltamethrin (from 4.4 to 48.9%). Anopheles gambiae s.l. from only one site (Bettie) were susceptible to chlorfenapyr at the dose of 100 µg active ingredient (a.i.)/bottle. At the dose of 200 µg (a.i.)/bottle, susceptibility was only recorded in 10 of the 15 sites.
    CONCLUSION: Low mosquito mortality was found for pyrethroids alone, and while PBO increased mortality, it did not restore full susceptibility. The vector was not fully susceptible to chlorfenapyr in one third of the sites tested. However, vector susceptibility to chlorfenapyr seems to be considerably higher than for pyrethroids alone or with PBO. These data should be used cautiously when making ITN procurement decisions, noting that bioassays are conducted in controlled conditions and may not fully represent field efficacy where the host-seeking behaviours, which include free-flying activity are known to enhance pro-insecticide chlorfenapyr intoxication to mosquitoes.
    Keywords:  Anopheles gambiae; Chlorfenapyr; Côte d’Ivoire; ITNs; Insecticide resistance; Piperonyl butoxide; Pyrethroids; Vector control
  2. Pest Manag Sci. 2020 Dec 10.
    Li Y, Zhou G, Zhong D, Wang X, Hemming-Schroeder E, David RE, Lee MC, Zhong S, Yi G, Liu Z, Cui G, Yan G.
      BACKGROUND: Aedes albopictus is a highly invasive mosquito and has become a potential vector of dengue, chikungunya and Zika viruses. Insecticide-based mosquito interventions are the main tools for vector-borne disease control. However, mosquito resistance to insecticides is a major threat to effective prevention and control. Five Ae. albopictus populations across Hainan Province, China were investigated for susceptibility to multiple insecticides and resistance mechanisms.RESULTS: Larval bioassays indicated that resistance to pyrethroids was common in all larval populations. Adult bioassays revealed all populations were either resistant or highly resistant to at least 4 of the 6 synthetic insecticides (deltamethrin, permethrin, cyfluthrin, propoxur, malathion, and DDT) tested. Pre-exposure of mosquitoes to the synergistic agent piperonyl butoxide (PBO) increased mosquito mortality by 2.4-43.3% in bioassays to DDT, malathion, and permethrin and rendered mosquito sensitive to deltamethrin, cyfluthrin, and propoxur. The frequency of knockdown resistance (kdr) mutations (F1534S and F1534C) ranged from 69.8% to 89.3% and from 38.1% to 87.0% in field resistant and sensitive populations, respectively. F1534S mutation was significantly associated with pyrethroid resistance. No mutation was detected in acetylcholinesterase (ace-1) gene in the two examined populations.
    CONCLUSION: This study provides evidence of widespread resistance to multiple insecticides in Ae. albopictus in Hainan Province, China. Both kdr mutations and metabolic detoxification were the potential causes of insecticide resistance for Ae. albopictus. Our findings highlight the need for insecticide resistance management and mosquito control measures that do not entirely depend on synthetic insecticides.
    Keywords:  Aedes albopictus; Hainan Province; insecticide resistance; knockdown resistance (kdr); piperonyl butoxide
  3. Dev Comp Immunol. 2020 Dec 07. pii: S0145-305X(20)30518-8. [Epub ahead of print]116 103964
    Tikhe CV, Dimopoulos G.
      Mosquitoes are vectors of a large number of viral pathogens. In recent years, increased urbanization and climate change has expanded the range of many vector mosquitoes. The lack of effective medical interventions has made the control of mosquito-borne viral diseases very difficult. Understanding the interactions between the mosquito immune system and viruses is critical if we are to develop effective control strategies against these diseases. Mosquitoes harbor multiple conserved immune pathways that curb invading viral pathogens. Despite the conservation of these pathways, the activation and intensity of the mosquito immune response varies with the mosquito species, tissue, and the infecting virus. This article reviews major conserved antiviral immune pathways in vector mosquitoes, their interactions with invading viral pathogens, and how these interactions restrict or promote infection of these medically important viruses.
    Keywords:  Antiviral; IMD; Immunity; JAK/STAT; Mosquito; RNAi; Toll
  4. J Med Entomol. 2020 Dec 09. pii: tjaa268. [Epub ahead of print]
    Ratisupakorn S, Lorn S, Dada N, Ngampongsai A, Chaivisit P, Ritthison W, Tainchum K.
      High rates of dengue morbidity occur in southern Thailand. The intensive application of insecticides in orchards could affect not only agricultural insect pests, but also nontarget mosquitoes or beneficial insects. In this study, the type and quantity of insecticides commonly used across durian plantations in southern Thailand were characterized, along with the population density of Aedes albopictus (Skuse) (Diptera: Culicidae). Our primary aim was to determine the susceptibility status of field-derived Ae. albopictus to typical application concentrations of four agrochemical insecticides; cypermethrin, chlorpyrifos, carbaryl, and imidacloprid. Mosquito eggs were collected from durian cultivation sites in five provinces in southern Thailand and used to generate adults for susceptibility tests. The cultivation sites were categorized into three groups based on insecticide application: intensive application of insecticides, low application of insecticides, and no application of insecticides. Twenty ovitraps were deployed for at least three consecutive days at each study site to collect mosquito eggs and to determine Ae. albopictus population density. WHO tube assays were used to determine the susceptibility of adult mosquitoes derived from field-collected eggs to selected insecticides. This represents the first report of the susceptibility status of Ae. albopictus from durian orchards in southern Thailand to agrochemical insecticides. Results showed complete susceptibility of these Ae. albopictus to chlorpyrifos, but reduced mortality following exposure to λ-cyhalothrin, carbaryl, and imidacloprid, which is suggestive of the development of resistance. These findings provide new insights into the status of insecticide susceptibility in Ae. albopictus populations, with important implications for mosquito and mosquito-borne disease control in Thailand.
    Keywords:   Aedes albopictus ; Thailand; agrochemical; durian; insecticide resistance
  5. PLoS Negl Trop Dis. 2020 Dec 07. 14(12): e0008949
    Saleh F, Kitau J, Konradsen F, Kampango A, Abassi R, Schiøler KL.
      BACKGROUND: In Zanzibar, little is known about the arboviral disease vector Aedes aegypti in terms of abundance, spatio-temporal distribution of its larval habitats or factors associated with its proliferation. Effective control of the vector requires knowledge on ecology and habitat characteristics and is currently the only available option for reducing the risk of arboviral epidemics in the island nation of Zanzibar.METHODOLOGY: We conducted entomological surveys in households and surrounding compounds from February to May 2018 in the urban (Mwembemakumbi and Chumbuni) and rural (Chuini and Kama) Shehias (lowest government administrative unit) situated in the Urban-West region of Unguja island, Zanzibar. Larvae and pupae were collected, transported to the insectary, reared to adult, and identified to species level. Characteristics and types of water containers were also recorded on site. Generalized linear mixed models with binomial and negative binomial distributions were applied to determine factors associated with presence of Ae. aegypti immatures (i.e. both larvae and pupae) or pupae, alone and significant predictors of the abundance of immature Ae. aegypti or pupae, respectively.
    RESULTS: The survey provided evidence of widespread presence and abundance of Ae. aegypti mosquitoes in both urban and rural settings of Unguja Island. Interestingly, rural setting had higher numbers of infested containers, all immatures, and pupae than urban setting. Likewise, higher House and Breteau indices were recorded in rural compared to the urban setting. There was no statistically significant difference in Stegomyia indices between seasons across settings. Plastics, metal containers and car tires were identified as the most productive habitats which collectively produced over 90% of all Ae. aegypti pupae. Water storage, sun exposure, vegetation, and organic matter were significant predictors of the abundance of immature Ae. aegypti.
    CONCLUSIONS: Widespread presence and abundance of Ae. aegypti were found in rural and urban areas of Unguja, the main island of Zanzibar. Information on productive habitats and predictors of colonization of water containers are important for the development of a routine Aedes surveillance system and targeted control interventions in Zanzibar and similar settings.
  6. PLoS Negl Trop Dis. 2020 Dec 09. 14(12): e0008918
    Elaagip A, Alsedig K, Altahir O, Ageep T, Ahmed A, Siam HA, Samy AM, Mohamed W, Khalid F, Gumaa S, Mboera L, Sindato C, Elton L, Zumla A, Haider N, Kock R, Abdel Hamid MM.
      Dengue is a rapidly growing public health threat in Kassala state, eastern Sudan. The objective of this study was to determine the seroprevalence, entomological transmission indices, and socioeconomic risk factors associated with dengue in this region. A cross-sectional community-based study was conducted in four dengue-endemic sites; Khatmia, West Gash, Thoriba, and Shokriya between March 2016 to March 2017. Enzyme-linked immunosorbent assay (ELISA) of immunoglobulin G (IgG) was used to determine the prevalence of dengue virus among the study participants. An entomological survey was conducted using pyrethrum spray catch and dipping for the collection of adults and aquatic stages of Aedes aegypti, respectively. Ribonucleic acid was extracted from the buffy coat of participants as well as from adult female Ae. aegypti to assess the possible circulation of dengue virus using Reverse Transcription Polymerase Chain Reaction (RT-PCR). Multiple logistic regression model was used to estimate the association between potential risk factors and dengue seropositivity. A total of 409 persons were recruited to the study: 45.5% were in the 20-39 years' age category; 57.9% were living in houses with 6-10 persons; and 29.1% had at most secondary school education. In the majority (65.8%) of the households, the socioeconomic status was low (P<0.001). Long-lasting insecticide-treated bed nets were used in 56.5% of the households. Over three-quarters (77.8%) claimed not to have experienced febrile illness in the last three months. Routine entomological survey across Kassala state identified a total of 3,304 larvae and 390 pupae Ae. aegypti, respectively. The overall house index was 32.8% and Breteau Index was 35.96% (146/406). The overall pupal demographic index was 13.31%, and the pupal children index was 97.26%. Antibodies against IgG were detected from 66 (42.04%) out of a total of 157 sera. Twenty-two positive sera (75.9%) were collected from Khatmia. A total of 329 adults Ae. aegypti were identified but only one (0.3%) was positive for DENV in Khatmia. Finally, four independent risk factors were identified to derive dengue circulation in Kassala: elder age (> 60 years) (OR 6.31, CI 1.09-36.36); type of bathroom (OR 3.52, CI 1.35-9.20); using water-based air conditioner (OR 6.90, CI 1.78-26.85) and previous infection of any household member with dengue (OR 28.73, CI 3.31-249.63). Our findings suggest that Kassala state is facing an increasing occurrence of dengue and emphasizes the need for developing appropriate interventions to address the identified risk factors, and place control programs into actions. Establishment of routine dengue epidemiological and entomological surveillance, and climate warning systems will contribute to early warning and timely detection and response to emerging outbreaks.
  7. Saudi J Biol Sci. 2020 Dec;27(12): 3359-3364
    Ali El Hadi Mohamed R, Abdelgadir DM, Bashab HM, Al-Shuraym LA, Sfouq Aleanizy F, Alqahtani FY, Ahmed Al-Keridis L, Mohamed N.
      This study aimed to explore the presence of West Nile Virus (WNV) inside four species of mosquitoes: Culex univittatus (Theobald), Culex quinquefasciatus (Say) Aedes vittatus (Bigot) and Aedes vexans (Meigen). Adult wild mosquitoes were collected from different sites: Soba West, Hellat Kuku, Shambat, and Khartoum North Central Live Stock Market (KCLM). Surveys were carried out at Khartoum State during two phases: pre to the rainy season and post to the rainy season. Mosquito specimens were identified using classical keys then preserved at -80 °C freezer for two weeks till the virus examination using polymerase chain reaction (PCR) were carried out. WNV has been detected inside the three species of mosquitoes: A. vexans, C. univittatus, and C. quinquefasciatus. The species were collected from Hellat Kuku, (Shambat and Hellat Kuku), and (Shambat and KCLM) respectively. Two species of mosquitoes were positive for the virus: C. quinquefasciatus and C. univittatus. Positive results for the virus during the first phase of the study; males of C. quinquefasciatus and C. univittatus collected during the second phase of the study were also tested for the existence of the virus and they were positive. For our knowledge this study represents first record of WNV inside wild mosquitoes in Sudan. PCR technique provided reliable information because specific primer-probe sets were used for the detection of the virus. Extra studies are required to incriminate these species of mosquitoes as potential vectors of WNV.
    Keywords:  Mosquitoes; Polymerase chain reaction; Sudan; West Nile Virus
  8. PLoS One. 2020 ;15(12): e0236607
    Ndiaye A, Niang EHA, Diène AN, Nourdine MA, Sarr PC, Konaté L, Faye O, Gaye O, Sy O.
      Despite the deployment of several effective control interventions in central-western Senegal, residual malaria transmission is still occurring in some hotspots. To better tailor targeted control actions, it is critical to unravel the underlying environmental and geographical factors that cause the persistence infection in hotspot villages. "Hotspots villages" were defined in our study as those reporting more than six indigenous malaria cases during the previous year. A total of ten villages, including seven hotspots and three non-hotspots, were surveyed. All potential mosquito breeding sites identified in and around the ten study villages were regularly monitored between 2013 and 2017. Monitoring comprised the detection of anopheline larvae and the collection of epidemiological, hydrogeological, topographical, and biogeographical data. The number of larval breeding sites described and monitored during the study period ranged from 50 to 62. Breeding sites were more numerous in hotspot sites in each year of monitoring, with 90.3% (56/62) in 2013, 90.9% (50/55) in 2014, 90.3% (56/62) in 2015 and 86% (43/50) in 2017 (Fisher exact test; p = 1). In the non-hotspot areas, the data for the same years were, respectively, 9.7% (6/62), 9.1% (5/55), 9.7% (6/62) and 14% (7/50) (p = 1). The Hotspot villages were characterized mostly by saline or moderately saline hydro-morphic and halomorphic soils allowing water retention and a potential larval breeding sites. By contrast, non-hotspot villages were characterized mainly by a high proportion of extremely permeable sandy-textured soils, which due to their porosity had low water retention. The annual number of confirmed malaria cases was correlated with the frequency and extent of breeding sites. Malaria cases were significantly more frequent in the hamlets located near breeding sites of An. gambiae s.l., gradually decreasing with increasing remoteness. This study shows that the characteristics of larval breeding sites, as measured by their longevity, stability, proximity to human habitation, and their positivity in Anopheles larvae are likely determining factors in the persistence of malaria hotspots in central-western Senegal. The results of this study shed more light on the environmental factors underlying the residual transmission and should make it possible to better target vector control interventions for malaria elimination in west-central Senegal.
  9. Sci Rep. 2020 Dec 10. 10(1): 21688
    Lorenz C, Castro MC, Trindade PMP, Nogueira ML, de Oliveira Lage M, Quintanilha JA, Parra MC, Dibo MR, Fávaro EA, Guirado MM, Chiaravalloti-Neto F.
      Identifying Aedes aegypti breeding hotspots in urban areas is crucial for the design of effective vector control strategies. Remote sensing techniques offer valuable tools for mapping habitat suitability. In this study, we evaluated the association between urban landscape, thermal features, and mosquito infestations. Entomological surveys were conducted between 2016 and 2019 in Vila Toninho, a neighborhood of São José do Rio Preto, São Paulo, Brazil, in which the numbers of adult female Ae. aegypti were recorded monthly and grouped by season for three years. We used data from 2016 to 2018 to build the model and data from summer of 2019 to validate it. WorldView-3 satellite images were used to extract land cover classes, and land surface temperature data were obtained using the Landsat-8 Thermal Infrared Sensor (TIRS). A multilevel negative binomial model was fitted to the data, which showed that the winter season has the greatest influence on decreases in mosquito abundance. Green areas and pavements were negatively associated, and a higher cover of asbestos roofs and exposed soil was positively associated with the presence of adult females. These features are related to socio-economic factors but also provide favorable breeding conditions for mosquitos. The application of remote sensing technologies has significant potential for optimizing vector control strategies, future mosquito suppression, and outbreak prediction.
  10. Sci Rep. 2020 Dec 10. 10(1): 21610
    Minal SP, Prakash S.
      The current study provides novel results on the synthesis of bimetallic nanoparticles (BNPs) of gold and palladium (Au-Pd) with an eco-friendly and non-toxic aqueous leaf extract of plant Citrus limon. The BNPs were characterized and toxicity bioassay was examined on the larvae of the pathogen vectors such as Anopheles stephensi and Aedes aegypti mosquitoes. The predation efficiency test was evaluated on the invertebrate non-target organisms such as natural predatory nymphs of dragonfly and damselfly. The results of material characterization using UV VIS spectroscopy confirmed the synthesis of Au-Pd BNPs with the appearance of the SPR bands. FT-IR spectroscopy indicates the presence of functional groups containing high amounts of nitro compounds and amines on the surface of BNPs. TEM result shows the presence of spherical polydisperse Au-Pd BNPs in the sample. The XRD pattern displayed the semi-crystalline nature and the changes in the hydrodynamic size and surface potential was determined for the sample at 0 h, 24 h, 48 h, and 72 h of synthesis through DLS and ZP analysis. Au-Pd BNPs Bioassay provided the effective lethal concentrations (LC50) against the I-IV instar larvae of An. stephensi and Ae. aegypti after 24 h, 48 h, and 72 h of exposure. The LC50 obtained from the larvicidal bioassay was used to test its effect on the predation efficiency of the selected nymphs which showed increased predation from 40 to 48 h of exposure as compared to the negative control. Hereby, we conclude that Au-Pd BNPs bioassay shows toxic mosquito larvicidal activity at the selected concentration with no lethal effect on the predation efficiency of the selected stage of the predatory non-target aquatic invertebrate insects.
  11. Chemosphere. 2021 Jan;pii: S0045-6535(20)32518-2. [Epub ahead of print]263 128323
    Schulte HL, Barreto Sousa JP, Sousa-Moura D, Grisolia CK, Espindola LS.
      Aedes aegypti is the main arbovirus vector transmitting chikungunya, Zika and dengue. The current vector control strategies are limited due to multiple insecticide resistance, deleterious impacts on the environment, and toxicity to non-target organisms. Bilobol, an alkylresorcinol isolated from the plant species Schinus terebinthifolia, demonstrated larvicidal activity against Aedes aegypti (LC50 7.67 mg/L in less than 24 h). To ensure that bilobol presents a viable alternative as an eco-friendly larvicide, this study aimed to explore the degradation process and acute toxicity of this alkylresorcinol in zebrafish, a non-target organism. A quantification method with validated parameters was developed and used to evaluate bilobol degradation in water over time. The Fish Embryo Toxicity (FET) test was applied to evaluate the acute toxicity of bilobol together with its degradation derivates. Results demonstrated that bilobol gradually degrades over time and almost completely disappears after 96 h, turning into small aliphatic chains which are less toxic than bilobol in its fundamental form. Therefore, it was possible to conclude that bilobol does not present significant toxicity to zebrafish embryos nor does it show signs of persistence in the environment. Additionally, bilobol can be found in high quantities not only in S. terebinthifolia, but also in cashew nut industry waste. Thus, bilobol constitutes an alternative environmentally friendly insecticide because it is not persistent, has indications of low toxicity to non-target organisms and presents a way to exploit massive quantities of material discarded by the food industry.
    Keywords:  Acute toxicity; Aedes aegypti; Bilobol; Bilobol quantification; Biodegradation; Larvicidal activity; Zebrafish
  12. J Med Entomol. 2020 Dec 08. pii: tjaa272. [Epub ahead of print]
    Holderman C, Abruzzo NO, Abdelsamad NA, Kaufman PE, DiGennaro PM.
      Dirofilaria immitis, the causative agent of dog heartworm disease, is an important cause of canine morbidity and mortality, expensive to treat, and severe infections are often fatal. Much is known about the pathogen in the canine host, yet little is known on the basic ecology of the nematode in the mosquito vector. Thus, to evaluate the effectiveness of collection techniques on ability to capture dog heartworm-infected mosquitoes (Diptera Culicidae), we conducted a field study spanning 111 wk. Four methods were used: two aspirators types, sweep netting, and a CDC trap. All sites had canines present in either residential yards (n = 4) or dog kennel facilities (n = 3). Collected mosquitoes were sorted by site, trap, species, and date, then pooled into groups of up to 25 individuals. Mosquito head and thorax pools were extracted for DNA, that was screened using currently available protocols. These protocols were found unreliable; thus, we developed a novel qPCR primer and probe set. Using this method, the original samples were re-assayed and provided 494 positive pools. Approximately 10% of positive samples were confirmed by Sanger sequencing. Twenty-two mosquito species tested positive for dog heartworm DNA, including a new association with Wyeomyia mitchellii (Theobald). Although Aedes atlanticus (Dyar and Knab), Anopheles crucians Wiedemann, and Culiseta melanura (Coquillett) composed nearly 36% of the total collection, these species represented 42% of the qPCR positive pools. Infection rates within commonly collected mosquitoes ranged up to 2.5%, with more rarely collected species ranging up to 14%. The CDC trap was the most effective collection method at trapping infected mosquitoes.
    Keywords:  Aedes; Anopheles; Culex; Psorophora; canine
  13. Parasit Vectors. 2020 Dec 09. 13(1): 613
    Dieme C, Ciota AT, Kramer LD.
      BACKGROUND: Mayaro virus (MAYV; Alphavirus, Togaviridae) is an emerging pathogen endemic in South American countries. The increase in intercontinental travel and tourism-based forest excursions has resulted in an increase in MAYV spread, with imported cases observed in Europe and North America. Intriguingly, no local transmission of MAYV has been reported outside South America, despite the presence of potential vectors.METHODS: We assessed the vector competence of Aedes albopictus from New York and Anopheles quadrimaculatus for MAYV.
    RESULTS: The results show that Ae. albopictus from New York and An. quadrimaculatus are competent vectors for MAYV. However, Ae. albopictus was more susceptible to infection. Transmission rates increased with time for both species, with rates of 37.16 and 64.44% for Ae. albopictus, and of 25.15 and 48.44% for An. quadrimaculatus, respectively, at 7 and 14 days post-infection.
    CONCLUSIONS: Our results suggest there is a risk of further MAYV spread throughout the Americas and autochthonous transmission in the USA. Preventive measures, such as mosquito surveillance of MAYV, will be essential for early detection.
    Keywords:  Aedes albopictus; Anopheles quadrimaculatus; Mayaro virus; Vector competence
  14. Int J Environ Res Public Health. 2020 Dec 07. pii: E9134. [Epub ahead of print]17(23):
    Doum D, Overgaard HJ, Mayxay M, Suttiprapa S, Saichua P, Ekalaksananan T, Tongchai P, Rahman MS, Haque U, Phommachanh S, Pongvongsa T, Rocklöv J, Paul R, Pientong C.
      Dengue is the most rapidly spreading mosquito-borne viral disease in the world. The detection of clinical cases enables us to measure the incidence of dengue infection, whereas serological surveys give insights into the prevalence of infection. This study aimed to determine dengue seroprevalence and seroconversion rates in northeastern Thailand and southern Laos and to assess any association of mosquito control methods and socioeconomic factors with dengue virus (DENV) infection. Cross-sectional seroprevalence surveys were performed in May and November 2019 on the same individuals. Blood samples were collected from one adult and one child, when possible, in each of 720 randomly selected households from two urban and two rural sites in both northeastern Thailand and southern Laos. IgG antibodies against DENV were detected in serum using a commercial enzyme-linked immunosorbent assay (ELISA) kit. Overall, 1071 individuals participated in the study. The seroprevalence rate was high (91.5%) across all 8 study sites. Only age and province were associated with seroprevalence rates. There were 33 seroconversions during the period from May to November, of which seven reported fever. More than half of the seroconversions occurred in the rural areas and in Laos. Dengue seroconversion was significantly associated with young age (<15 years old), female gender, province, and duration of living in the current residence. No socioeconomic factors or mosquito control methods were found to be associated with seroprevalence or seroconversion. Notably, however, the province with most seroconversions had lower diurnal temperature ranges than elsewhere. In conclusion, our study has highlighted the homogeneity of dengue exposure across a wide range of settings and most notably those from rural and urban areas. Dengue can no longer be considered to be solely an urban disease nor necessarily one linked to poverty.
    Keywords:  DENV; dengue; seroconversion; seroprevalence; socioeconomic factors
  15. Insect Biochem Mol Biol. 2020 Dec 03. pii: S0965-1748(20)30189-2. [Epub ahead of print]128 103500
    Che LR, He ZB, Liu Y, Yan ZT, Han BZ, Chen XJ, He XF, Zhang JJ, Chen B, Qiao L.
      The delivery of exogenous nucleic acids to eggs or non-embryonic individuals by microinjection is a vital reverse genetics technique used to determine gene function in mosquitoes. However, DNA delivery to eggs is complex and time-consuming, and conventional, non-embryonic-injection techniques may result in unobvious phenotypes caused by insufficient absorption of nucleic acid fragments by cells at target body parts or tissues. In this study, we developed a set of electroporation-mediated non-embryonic microinjections for the delivery of exogenous nucleic acids in Anopheles sinensis. Gene silencing using this method led to down-regulation of target gene expression (AsCPR128) by 77% in targeted body parts, compared with only 10% in non-targeted body parts, thus increasing the defect-phenotype rate in the target area by 5.3-fold, compared with non-shock injected controls. Electroporation-mediated somatic transgenesis resulted in stable phenotypic characteristics of the reporter gene at the shocked body parts during the pupal-adult stages in about 69% of individuals. Furthermore, injecting plasmid DNA near the ovaries of female mosquitoes after a blood meal followed by electric shock produced three germline G1 transgenic lines, with a transformation rate of about 11.1% (calculated from ovulatory G0 females). Among the positive G1 lines, 42%, 40%, and 31% of individuals emitted red fluorescence in the larval stage. When the red fluorescent larvae developed into adults, green fluorescence was emitted from the ovaries of the females upon feeding. These results suggest that electroporation-mediated non-embryonic microinjection can be an efficient, rapid, and simple technique for analyzing gene function in non-model mosquitoes or other small insects.
    Keywords:  Anopheles sinensis; Electroporation-mediated non-embryonic microinjection; Germline transgenesis; Nucleic acid delivery; RNAi; Somatic transgenesis
  16. J Infect Dis. 2020 Dec 11. pii: jiaa759. [Epub ahead of print]
    Chuang YM, Agunbiade TA, Tang XD, Freudzon M, Almeras L, Fikrig E.
      Malaria begins when Plasmodium-infected Anopheles mosquitoes take a blood meal on a vertebrate. During the initial probing process, mosquitoes inject saliva and sporozoites into the host skin. Components of mosquito saliva have the potential to influence sporozoite functionality. Sporozoite-associated mosquito saliva protein 1 (SAMSP1, AGAP013726) was among several proteins identified when sporozoites were isolated from saliva, suggesting it may have an effect on Plasmodium. Recombinant SAMSP1 enhanced sporozoite gliding and cell traversal activity in vitro. Moreover, SAMSP1 decreased neutrophil chemotaxis in vivo and in vitro, thereby also exerting an influence on the host environment in which the sporozoites reside. Active or passive immunization of mice with SAMSP1 or SAMSP1 antisera diminished the initial Plasmodium burden following infection. Passive immunization of mice with SAMSP1 antisera also added to the protective effect of a circumsporozoite protein (CSP) monoclonal antibody. SAMSP1 is, therefore, a mosquito saliva protein that can influence sporozoite infectivity in the vertebrate host.
    Keywords:  cell traversal; gliding; mosquito; saliva protein; sporozoite
  17. Malar J. 2020 Dec 07. 19(1): 452
    Nasir SMI, Amarasekara S, Wickremasinghe R, Fernando D, Udagama P.
      Prevention of re-establishment (POR) refers to the prevention of malaria outbreak/epidemic occurrence or preventing re-establishment of indigenous malaria in a malaria-free country. Understanding the effectiveness of the various strategies used for POR is, therefore, of vital importance to countries certified as "malaria-free" or to the countries to be thus certified in the near future. This review is based on extensive review of literature on both the POR strategies and elimination schemes of countries, (i) that have reached malaria-free status (e.g. Armenia, Mauritius, Sri Lanka), (ii) those that are reaching pre-elimination stage (e.g. South Korea), and (iii) countries at the control phase (e.g. India). History has clearly shown that poorly implemented POR programmes can result in deadly consequences (e.g. Sri Lanka); conversely, there are examples of robust POR programmes that have sustained malaria free status that can serve as examples to countries working toward elimination. Countries awaiting malaria elimination status should pre-plan their POR strategies. Malaria-free countries face the risk of resurgence mostly due to imported malaria cases; thus, a robust passenger screening programme and cross border collaborations are crucial in a POR setting. In addition, sustained vigilance, and continued funding for the national anti-malarial campaign programme and for related research is of vital importance for POR. With distinct intrinsic potential for malaria in each country, tailor-made POR programmes are built through continuous and robust epidemiological and entomological surveillance, particularly in countries such as Sri Lanka with increased receptivity and vulnerability for malaria transmission. In summary, across all five countries under scrutiny, common strengths of the POR programmes are (i) a multipronged approach, (ii) strong passive, active, and activated passive case detection, (iii) Indoor residual spraying (IRS), and (iv) health education/awareness programmes.
    Keywords:  Importation risk; Malaria elimination; Plasmodium falciparum; Plasmodium vivax; Prevention of re-establishment; Receptivity; Surveillance; Vulnerability
  18. Ecol Lett. 2020 Dec 10.
    Nova N, Deyle ER, Shocket MS, MacDonald AJ, Childs ML, Rypdal M, Sugihara G, Mordecai EA.
      Experiments and models suggest that climate affects mosquito-borne disease transmission. However, disease transmission involves complex nonlinear interactions between climate and population dynamics, which makes detecting climate drivers at the population level challenging. By analysing incidence data, estimated susceptible population size, and climate data with methods based on nonlinear time series analysis (collectively referred to as empirical dynamic modelling), we identified drivers and their interactive effects on dengue dynamics in San Juan, Puerto Rico. Climatic forcing arose only when susceptible availability was high: temperature and rainfall had net positive and negative effects respectively. By capturing mechanistic, nonlinear and context-dependent effects of population susceptibility, temperature and rainfall on dengue transmission empirically, our model improves forecast skill over recent, state-of-the-art models for dengue incidence. Together, these results provide empirical evidence that the interdependence of host population susceptibility and climate drives dengue dynamics in a nonlinear and complex, yet predictable way.
    Keywords:  Arbovirus; climate; dengue; empirical dynamic modelling; forecasting; rainfall; susceptible population size; temperature; vector-borne disease
  19. Public Health Res Pract. 2020 Dec 09. pii: 3042027. [Epub ahead of print]30(4):
    Webb CE.
      Mosquitoes and mosquito-borne disease are a normal part of the Australian summer but the 2019-2020 summer was anything but normal. Above average temperatures and below average rainfall resulted in drought across many parts of New South Wales (NSW), Australia, which then contributed to catastrophic bushfires. However, by late summer, above average rainfall resulted in a dramatic increase in mosquito abundance. While the coronavirus disease 2019 (COVID-19) pandemic unfolded, NSW experienced increased activity of mosquito-borne Ross River virus. All these extreme events created many challenges for managing the pest and the public health risks associated with mosquitoes, from maintenance of mosquito monitoring and control programs through to unique challenges of communicating mosquito bite prevention advice to local communities. There are important lessons to be learned in situations where extreme weather events may influence the risk of mosquito-borne disease through driving changes in the abundance and diversity of mosquito populations, while also influencing the abundance and distribution of native wildlife that represents important local reservoirs of arboviruses. Similarly, supporting the maintenance of mosquito monitoring and management programs while local authorities face competing priorities due to extreme natural disasters and/or public health events is critical.
  20. J Infect Dev Ctries. 2020 Nov 30. 14(11): 1332-1337
    Amer OS, Waly MI, Burhan IW, Al-Malki ES, Smida A, Al-Benasy KS.
      INTRODUCTION: Saudi Arabia has successfully reduced malaria cases to be constrained largely in the western regions. This study aimed to determine the epidemiological trends of malaria infection in five western regions of Saudi Arabia.METHODOLOGY: A retrospective analysis was conducted to investigate the epidemiological trends of malaria infection in the western regions, based on the published registry of the Saudi Ministry of Health, during the period from 2014 to 2017 using the appropriate statistical tools.
    RESULTS: A total of 8925 confirmed cases of malaria were reported in the western regions during the period from 2014 to 2017 with the mean of 2231 malaria cases per year. The minimum (n = 1097) and maximum (n = 4075) number of cases were reported in 2014 and 2016 respectively. The highest (n = 5919, 66.3%) number of cases were reported from Jazan region, while lowest (n = 86, 1.0%) number of cases were reported from Al-Bahah region. Plasmodium falciparum was the most frequently reported species with 7485 (83.9%) cases, while Plasmodium vivax accounted 1386 (15.5%) cases. Plasmodium malariae and mixed infections were insignificant and accounted 0.5% (n = 48) and 0.1% (n = 6) cases respectively. In relation to malaria infection and age group, malaria was predominant in > 15 age group. The highest number of malaria cases in almost all years was observed from January until March and the lowest number was reported from May until July.
    CONCLUSIONS: Plasmodium falciparum was the most dominant species in this survey and Jazan was the most affected region.
    Keywords:  Cross sectional study; Epidemiological trends; Saudi Arabia; Western Region; malaria
  21. PLoS One. 2020 ;15(12): e0233478
    Myers-Hansen JL, Abuaku B, Oyebola MK, Mensah BA, Ahorlu C, Wilson MD, Awandare G, Koram KA, Ngwa AA, Ghansah A.
      BACKGROUND: Drug resistance remains a concern for malaria control and elimination. The effect of interventions on its prevalence needs to be monitored to pre-empt further selection. We assessed the prevalence of Plasmodium falciparum gene mutations associated with resistance to the antimalarial drugs: sulfadoxine-pyrimethamine (SP), chloroquine (CQ) and artemisinin combination therapy (ACTs) after the scale-up of a vector control activity that reduced transmission.METHODS: A total of 400 P. falciparum isolates from children under five years were genotyped for seventeen single nucleotide polymorphisms (SNPs) in pfcrt, pfmdr1, pfdhfr, pfdhps and pfk13 genes using polymerase chain reaction (PCR) and high resolution melting (HRM) analysis. These included 80 isolates, each randomly selected from cross-sectional surveys of asymptomatic infections across 2010 (baseline), 2011, 2012, 2013 (midline: post-IRS) and 2014 (endline: post-IRS) during the peak transmission season, when IRS intervention was rolled out in Bunkpurugu Yunyoo (BY) District, Ghana. The proportions of isolates with drug resistant alleles were assessed over this period.
    RESULTS: There were significant decreases in the prevalence of pfdhfr- I51R59N108 haplotype from 2010 to 2014, while the decline in pfdhfr/pfdhps- I51R59N108G437 during the same period was not significant. The prevalence of lumefantrine (LM), mefloquine (MQ) and amodiaquine (AQ) resistance-associated haplotypes pfmdr1-N86F184D1246 and pfmdr1-Y86Y184Y1246 showed decreasing trends (z = -2.86, P = 0.004 and z = -2.71, P = 0.007, respectively). Each of pfcrt-T76 and pfmdr1-Y86 mutant alleles also showed a declining trend in the asymptomatic reservoir, after the IRS rollout in 2014 (z = -2.87, P = 0.004 and z = -2.65, P = 0.008, respectively). Similarly, Pyrimethamine resistance mediating polymorphisms pfdhfr-N108, pfdhfr-I51 and pfdhfr-R59 also declined (z = -2.03, P = 0.042, z = -3.54, P<0.001 and z = -4.63, P<0.001, respectively), but not the sulphadoxine resistance mediating pfdhps-G437 and pfdhps-F436 (z = -0.36, P = 0.715 and z = 0.41, P = 0.684, respectively). No mutant pfk13-Y580 were detected during the study period.
    CONCLUSION: The study demonstrated declining trends in the prevalence of drug resistant mutations in asymptomatic P. falciparum infections following transmission reduction after an enhanced IRS intervention in Northern Ghana.