bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2021‒05‒30
eighteen papers selected by
Richard Halfpenny
Staffordshire University

  1. BMC Res Notes. 2021 May 22. 14(1): 200
      OBJECTIVE: In the framework of EVALMOUS study aiming to assess the use and effectiveness of mosquito nets by pregnant women and other members of their household in a lagoon area in southern Benin, the behaviour of pregnant women relative to the time they go to bed using the net were recorded. Malaria vectors biting rhythm, Plasmodium falciparum infection and insecticide resistance genes in malaria vectors were also determined.RESULTS: Overall, 3848 females of Anopheles gambiae s. l were collected and 280 pregnant women responded to the survey. Almost all Anopheles gambiae s. l. tested were Anopheles coluzzi Coetzee and Wilkerson 2013 (Diptera: Culicidae). The CSP index in malaria vector was 1.85% and the allelic frequency of kdr gene was 74.4%. Around 90% of bites and Plasmodium falciparum Welch, 1897 (Haemosporida: Plasmodiidae) transmission occurred between 10 p.m. and 6 a.m., which coincides with the period when more than 80% of pregnant women were under bednet. Despite a slight early evening and early morning biting activity of malaria vectors in the study area, the good use of nets might remain a useful protection tool against mosquito biting and malaria transmission.
    Keywords:  Anopheles coluzzi; Biting rhythm; Malaria; Pregnant women; Prevention
  2. Cochrane Database Syst Rev. 2021 May 24. 5 CD012776
      BACKGROUND: Pyrethroid long-lasting insecticidal nets (LLINs) have been important in the large reductions in malaria cases in Africa, but insecticide resistance in Anopheles mosquitoes threatens their impact. Insecticide synergists may help control insecticide-resistant populations. Piperonyl butoxide (PBO) is such a synergist; it has been incorporated into pyrethroid-LLINs to form pyrethroid-PBO nets, which are currently produced by five LLIN manufacturers and, following a recommendation from the World Health Organization (WHO) in 2017, are being included in distribution campaigns. This review examines epidemiological and entomological evidence on the addition of PBO to pyrethroid nets on their efficacy.OBJECTIVES: To compare effects of pyrethroid-PBO nets currently in commercial development or on the market with effects of their non-PBO equivalent in relation to: 1. malaria parasite infection (prevalence or incidence); and 2. entomological outcomes.
    SEARCH METHODS: We searched the Cochrane Infectious Diseases Group (CIDG) Specialized Register, CENTRAL, MEDLINE, Embase, Web of Science, CAB Abstracts, and two clinical trial registers ( and WHO International Clinical Trials Registry Platform) up to 25 September 2020. We contacted organizations for unpublished data. We checked the reference lists of trials identified by these methods.
    SELECTION CRITERIA: We included experimental hut trials, village trials, and randomized controlled trials (RCTs) with mosquitoes from the Anopheles gambiae complex or the Anopheles funestus group.
    DATA COLLECTION AND ANALYSIS: Two review authors assessed each trial for eligibility, extracted data, and determined the risk of bias for included trials. We resolved disagreements through discussion with a third review author. We analysed data using Review Manager 5 and assessed the certainty of evidence using the GRADE approach.
    MAIN RESULTS: Sixteen trials met the inclusion criteria: 10 experimental hut trials, four village trials, and two cluster-RCTs (cRCTs). Three trials are awaiting classification, and four trials are ongoing.  Two cRCTs examined the effects of pyrethroid-PBO nets on parasite prevalence in people living in areas with highly pyrethroid-resistant mosquitoes (< 30% mosquito mortality in discriminating dose assays). At 21 to 25 months post intervention, parasite prevalence was lower in the intervention arm (odds ratio (OR) 0.79, 95% confidence interval (CI) 0.67 to 0.95; 2 trials, 2 comparisons; moderate-certainty evidence). In highly pyrethroid-resistant areas, unwashed pyrethroid-PBO nets led to higher mosquito mortality compared to unwashed standard-LLINs (risk ratio (RR) 1.84, 95% CI 1.60 to 2.11; 14,620 mosquitoes, 5 trials, 9 comparisons; high-certainty evidence) and lower blood feeding success (RR 0.60, 95% CI 0.50 to 0.71; 14,000 mosquitoes, 4 trials, 8 comparisons; high-certainty evidence). However, in comparisons of washed pyrethroid-PBO nets to washed LLINs, we do not know if PBO nets had a greater effect on mosquito mortality (RR 1.20, 95% CI 0.88 to 1.63; 10,268 mosquitoes, 4 trials, 5 comparisons; very low-certainty evidence), although the washed pyrethroid-PBO nets did decrease blood-feeding success compared to standard-LLINs (RR 0.81, 95% CI 0.72 to 0.92; 9674 mosquitoes, 3 trials, 4 comparisons; high-certainty evidence). In areas where pyrethroid resistance is moderate (31% to 60% mosquito mortality), mosquito mortality was higher with unwashed pyrethroid-PBO nets compared to unwashed standard-LLINs (RR 1.68, 95% CI 1.33 to 2.11; 751 mosquitoes, 2 trials, 3 comparisons; moderate-certainty evidence), but there was little to no difference in effects on blood-feeding success (RR 0.90, 95% CI 0.72 to 1.11; 652 mosquitoes, 2 trials, 3 comparisons; moderate-certainty evidence). For washed pyrethroid-PBO nets compared to washed standard-LLINs, we found little to no evidence for higher mosquito mortality or reduced blood feeding (mortality: RR 1.07, 95% CI 0.74 to 1.54; 329 mosquitoes, 1 trial, 1 comparison, low-certainty evidence; blood feeding success: RR 0.91, 95% CI 0.74 to 1.13; 329 mosquitoes, 1 trial, 1 comparison; low-certainty evidence). In areas where pyrethroid resistance is low (61% to 90% mosquito mortality), studies reported little to no difference in the effects of unwashed pyrethroid-PBO nets compared to unwashed standard-LLINs on mosquito mortality (RR 1.25, 95% CI 0.99 to 1.57; 948 mosquitoes, 2 trials, 3 comparisons; moderate-certainty evidence), and we do not know if there was any effect on blood-feeding success (RR 0.75, 95% CI 0.27 to 2.11; 948 mosquitoes, 2 trials, 3 comparisons; very low-certainty evidence). For washed pyrethroid-PBO nets compared to washed standard-LLINs, we do not know if there was any difference in mosquito mortality (RR 1.39, 95% CI 0.95 to 2.04; 1022 mosquitoes, 2 trials, 3 comparisons; very low-certainty evidence) or on blood feeding (RR 1.07, 95% CI 0.49 to 2.33; 1022 mosquitoes, 2 trials, 3 comparisons; low-certainty evidence). In areas where mosquito populations are susceptible to insecticides (> 90% mosquito mortality), there may be little to no difference in the effects of unwashed pyrethroid-PBO nets compared to unwashed standard-LLINs on mosquito mortality (RR 1.20, 95% CI 0.64 to 2.26; 2791 mosquitoes, 2 trials, 2 comparisons; low-certainty evidence). This is similar for washed nets (RR 1.07, 95% CI 0.92 to 1.25; 2644 mosquitoes, 2 trials, 2 comparisons; low-certainty evidence). We do not know if unwashed pyrethroid-PBO nets had any effect on the blood-feeding success of susceptible mosquitoes (RR 0.52, 95% CI 0.12 to 2.22; 2791 mosquitoes, 2 trials, 2 comparisons; very low-certainty evidence). The same applies to washed nets (RR 1.25, 95% CI 0.82 to 1.91; 2644 mosquitoes, 2 trials, 2 comparisons; low-certainty evidence). In village trials comparing pyrethroid-PBO nets to LLINs, there was no difference in sporozoite rate (4 trials, 5 comparisons) nor in mosquito parity (3 trials, 4 comparisons).
    AUTHORS' CONCLUSIONS: In areas of high insecticide resistance, pyrethroid-PBO nets have greater entomological and epidemiological efficacy compared to standard LLINs, with sustained reduction in parasite prevalence, higher mosquito mortality and reduction in mosquito blood feeding rates 21 to 25 months post intervention. Questions remain about the durability of PBO on nets, as the impact of pyrethroid-PBO nets on mosquito mortality was not sustained over 20 washes in experimental hut trials, and epidemiological data on pyrethroid-PBO nets for the full intended three-year life span of the nets is not available. Little evidence is available to support greater entomological efficacy of pyrethroid-PBO nets in areas where mosquitoes show lower levels of resistance to pyrethroids.
  3. Parasit Vectors. 2021 May 22. 14(1): 272
      BACKGROUND: Botanical substances such as essential oils (EOs) have demonstrated insecticidal properties and are a valid option for vector control. However, free EOs are unreliable as mosquito larvicides due their easy degradation by environmental exposure to ultraviolet light and higher temperatures. Here, we assessed the efficacy of a mosquito larvicide based on orange oil in a yeast-based delivery system against Aedes aegypti strains with different resistance status towards chemical neurotoxic insecticides. This larvicide preparation was physicochemically characterized in a previous report.METHODS: Larvae of four Ae. aegypti strains from different regions of Brazil and different resistance profiles for deltamethrin (pyrethroid) and temephos (organophosphate) were tested against yeast-encapsulated orange oil (YEOO) in laboratory conditions for measurement of LC50 and LC90 values. The same assays were performed with the Belo Horizonte strain under environmental conditions (natural light and temperature). The resistance profiles of these strains were compared to the Rockefeller reference strain in all conditions.
    RESULTS: YEOO was found to be a highly active larvicide (LC50 < 50 mg/L) against all Ae. aegypti strains tested in both laboratory conditions (LC50 = 8.1-24.7 mg/L) and environmental conditions with natural light and temperature fluctuation (LC50 = 20.0-49.9 mg/L). Moreover, all strains were considered susceptible (RR < 5) to YEOO, considering resistance ratios calculated based on the Rockefeller strain. The resistance ratios were only higher than 2.5 for LC90-95 of Belo Horizonte in the laboratory, probably due the higher heterogeneity associated with older egg papers (> 5 months).
    CONCLUSION: YEOO demonstrates high larvicidal activity against Ae. aegypti strains with resistant phenotypes for deltamethrin (PY) and temephos (OP). This larvicidal activity suggests the potential for the development of YEOO as an alternative intervention to synthetic insecticides in integrated vector management programs, for populations with resistance to commonly used insecticides.
    Keywords:  Aedes aegypti; Arbovirus; Citrus sinensis; Dengue; Mosquito control
  4. J R Soc Interface. 2021 May;18(178): 20210256
      Most malaria infections in sub-Saharan Africa are acquired indoors, thus finding effective ways of preventing mosquito house entry should reduce transmission. Since most malaria mosquitoes fly less than 1 m from the ground, we tested whether raising buildings off the ground would prevent the entry of Anopheles gambiae, the principal African malaria vector, in rural Gambia. Nightly collections of mosquitoes were made using light traps from four inhabited experimental huts, each of which could be moved up or down. Mosquito house entry declined with increasing height, with a hut at 3 m reducing An. gambiae house entry by 84% when compared with huts on the ground. A propensity for malaria vectors to fly close to the ground and reduced levels of carbon dioxide, a major mosquito attractant, in elevated huts, may explain our findings. Raised buildings may help reduce malaria transmission in Africa.
    Keywords:  Anopheles gambiae; housing; malaria; mosquitoes; sub-Saharan Africa
  5. Proc Natl Acad Sci U S A. 2021 Jun 01. pii: e2004838117. [Epub ahead of print]118(22):
      CRISPR-Cas9 nuclease-based gene drives have been developed toward the aim of control of the human malaria vector Anopheles gambiae Gene drives are based on an active source of Cas9 nuclease in the germline that promotes super-Mendelian inheritance of the transgene by homology-directed repair ("homing"). Understanding whether CRISPR-induced off-target mutations are generated in Anopheles mosquitoes is an important aspect of risk assessment before any potential field release of this technology. We compared the frequencies and the propensity of off-target events to occur in four different gene-drive strains, including a deliberately promiscuous set-up, using a nongermline restricted promoter for SpCas9 and a guide RNA with many closely related sites (two or more mismatches) across the mosquito genome. Under this scenario we observed off-target mutations at frequencies no greater than 1.42%. We witnessed no evidence that CRISPR-induced off-target mutations were able to accumulate (or drive) in a mosquito population, despite multiple generations' exposure to the CRISPR-Cas9 nuclease construct. Furthermore, judicious design of the guide RNA used for homing of the CRISPR construct, combined with tight temporal constriction of Cas9 expression to the germline, rendered off-target mutations undetectable. The findings of this study represent an important milestone for the understanding and managing of CRISPR-Cas9 specificity in mosquitoes, and demonstrates that CRISPR off-target editing in the context of a mosquito gene drive can be reduced to minimal levels.
    Keywords:  Anopheles; CRISPR-Cas; gene drive; off-target; vector control
  6. PLoS One. 2021 ;16(5): e0252369
      Aedes aegypti and Culex pipiens complex mosquitoes are prolific vectors of arboviruses that are a global threat to human and animal health. Increased globalization and ease of travel have facilitated the worldwide dissemination of these mosquitoes and the viruses they transmit. To assess disease risk, we determined the frequency of arboviruses in western Kenyan counties bordering an area of high arboviral activity. In addition to pathogenic viruses, insect-specific flaviviruses (ISFs), some of which are thought to impair the transmission of specific pathogenic arboviruses, were also evaluated. We trapped mosquitoes in the short and long rainy seasons in 2018 and 2019 at livestock markets and hospitals. Mosquitoes were screened for dengue, chikungunya and other human pathogenic arboviruses, ISFs, and their blood-meal sources as determined by high-resolution melting analysis of (RT-)PCR products. Of 6,848 mosquitoes collected, 89% were trapped during the long rainy season, with A. aegypti (59%) and Cx. pipiens sensu lato (40%) being the most abundant. Most blood-fed mosquitoes were Cx. pipiens s.l. with blood-meals from humans, chicken, and sparrow (Passer sp.). We did not detect dengue or chikungunya viruses. However, one Culex poicilipes female was positive for Sindbis virus, 30 pools of Ae. aegypti had cell fusing agent virus (CFAV; infection rate (IR) = 1.27%, 95% CI = 0.87%-1.78%); 11 pools of Ae. aegypti had Aedes flavivirus (AeFV; IR = 0.43%, 95% CI = 0.23%-0.74%); and seven pools of Cx. pipiens s.l. (IR = 0.23%, 95% CI = 0.1%-0.45%) and one pool of Culex annulioris had Culex flavivirus. Sindbis virus, which causes febrile illness in humans, can complicate the diagnosis and prognosis of patients with fever. The presence of Sindbis virus in a single mosquito from a population of mosquitoes with ISFs calls for further investigation into the role ISFs may play in blocking transmission of other arboviruses in this region.
  7. Malar J. 2021 May 22. 20(1): 232
      BACKGROUND: Current standard interventions are not universally sufficient for malaria elimination. The effects of community-based house improvement (HI) and larval source management (LSM) as supplementary interventions to the Malawi National Malaria Control Programme (NMCP) interventions were assessed in the context of an intensive community engagement programme.METHODS: The study was a two-by-two factorial, cluster-randomized controlled trial in Malawi. Village clusters were randomly assigned to four arms: a control arm; HI; LSM; and HI + LSM. Malawi NMCP interventions and community engagement were used in all arms. Household-level, cross-sectional surveys were conducted on a rolling, 2-monthly basis to measure parasitological and entomological outcomes over 3 years, beginning with one baseline year. The primary outcome was the entomological inoculation rate (EIR). Secondary outcomes included mosquito density, Plasmodium falciparum prevalence, and haemoglobin levels. All outcomes were assessed based on intention to treat, and comparisons between trial arms were conducted at both cluster and household level.
    RESULTS: Eighteen clusters derived from 53 villages with 4558 households and 20,013 people were randomly assigned to the four trial arms. The mean nightly EIR fell from 0.010 infectious bites per person (95% CI 0.006-0.015) in the baseline year to 0.001 (0.000, 0.003) in the last year of the trial. Over the full trial period, the EIR did not differ between the four trial arms (p = 0.33). Similar results were observed for the other outcomes: mosquito density and P. falciparum prevalence decreased over 3 years of sampling, while haemoglobin levels increased; and there were minimal differences between the trial arms during the trial period.
    CONCLUSIONS: In the context of high insecticide-treated bed net use, neither community-based HI, LSM, nor HI + LSM contributed to further reductions in malaria transmission or prevalence beyond the reductions observed over two years across all four trial arms. This was the first trial, as far as the authors are aware, to test the potential complementary impact of LSM and/or HI beyond levels achieved by standard interventions. The unexpectedly low EIR values following intervention implementation indicated a promising reduction in malaria transmission for the area, but also limited the usefulness of this outcome for measuring differences in malaria transmission among the trial arms. Trial registration PACTR, PACTR201604001501493, Registered 3 March 2016, .
    Keywords:  Cluster randomised trial; Community engagement; House improvement; Larval source management; Malaria
  8. Int J Infect Dis. 2021 May 24. pii: S1201-9712(21)00453-7. [Epub ahead of print]
      OBJECTIVES: The aim of this study was to investigate an outbreak of a non-malaria undifferentiated febrile illness among internally displaced persons (IDPs) living in humanitarian camps in North Darfur, Sudan in 2019.METHODS: An investigation team was deployed to the State to identify and collect blood samples, clinical and demographical data from the suspected-cases. Blood samples were examined forPlasmodium falciparum using microscope and tested for dengue (DENV) and Yellow fever viruses using commercial RT-qPCR kits.
    RESULTS: Between September 7th and December 18th, 2019, we clinically identified 18 (24%), 41 (54%), and 17 (22%) cases of dengue fever, dengue with warning signs, and severe dengue, respectively. Blood samples were collected from 20% of patients, and 47% of them tested positive for DENV-1 RNA. We confirmed 32 malaria cases with five co-infections with DENV. This is the first outbreak of dengue among IDPs in the humanitarian camps.
    CONCLUSIONS: This either indicates that the virus has become endemic or that there has been a new introduction. Further epidemiological, entomological, and phylogenetic studies are needed to understand the disease transmission in the area. An early warning and response system along with an effective health policy is crucial for the prevention and control of arboviruses in the country.
    Keywords:  Dengue with warning signs (DWWS); Sudan; arboviruses; epidemic; outbreak; severe dengue fever (SD)
  9. J R Soc Interface. 2021 May;18(178): 20210049
      Vector-borne diseases (VBDs), such as dengue, Zika, West Nile virus (WNV) and tick-borne encephalitis, account for substantial human morbidity worldwide and have expanded their range into temperate regions in recent decades. Climate change has been proposed as a likely driver of past and future expansion, however, the complex ecology of host and vector populations and their interactions with each other, environmental variables and land-use changes makes understanding the likely impacts of climate change on VBDs challenging. We present an environmentally driven, stage-structured, host-vector mathematical modelling framework to address this challenge. We apply our framework to predict the risk of WNV outbreaks in current and future UK climates. WNV is a mosquito-borne arbovirus which has expanded its range in mainland Europe in recent years. We predict that, while risks will remain low in the coming two to three decades, the risk of WNV outbreaks in the UK will increase with projected temperature rises and outbreaks appear plausible in the latter half of this century. This risk will increase substantially if increased temperatures lead to increases in the length of the mosquito biting season or if European strains show higher replication at lower temperatures than North American strains.
    Keywords:  West Nile virus; climate change; delay-differential equations; mathematical model; mosquito; vector-borne diseases
  10. Sci Total Environ. 2021 Jul 15. pii: S0048-9697(21)01195-5. [Epub ahead of print]778 146128
      Aedes aegypti and Aedes albopictus transmit diseases such as dengue, and are of major public health concern. Driven by climate change and global trade/travel both species have recently spread to new tropic/subtropic regions and Ae. albopictus also to temperate ecoregions. The capacity of both species to adapt to new environments depends on their ecophysiological plasticity, which is the width of functional niches where a species can survive. Mechanistic distribution models often neglect to incorporate ecophysiological plasticity especially in regards to overwintering capacity in cooler habitats. To portray the ecophysiological plasticity concerning overwintering capability, we conducted temperature experiments with multiple populations of both species originating from an altitudinal gradient in South Asia and tested as follows: the cold tolerance of eggs (-2 °C- 8 days and - 6 °C- 2 days) without and with an experimental winter onset (acclimation: 10 °C- 60 days), differences between a South Asian and a European Ae. albopictus population and the temperature response in life cycles (13 °C, 18 °C, 23 °C, 28 °C). Ecophysiological plasticity in overwintering capacity in Ae. aegypti is high in populations originating from low altitude and in Ae. albopictus populations from high altitude. Overall, ecophysiological plasticity is higher in Ae. albopictus compared to Ae. aegypti. In both species acclimation and in Ae. albopictus temperate continental origin had a huge positive effect on survival. Our results indicate that future mechanistic prediction models can include data on winter survivorship of both, tropic and subtropic Ae. aegypti, whereas for Ae. albopictus this depends on the respective temperate, tropical region the model is focusing on. Future research should address cold tolerance in multiple populations worldwide to evaluate the full potential of the ecophysiological plasticity in the two species. Furthermore, we found that Ae. aegypti can survive winter cold especially when acclimated and will probably further spread to colder ecoregions driven by climate change.
    Keywords:  Climate change; Cold tolerance; Distribution limits; Invasion biology; Overwintering capacity; Winter survival
  11. Evol Appl. 2021 May;14(5): 1301-1313
      Local adaptation is important when predicting arthropod-borne disease risk because of its impacts on vector population fitness and persistence. However, the extent that vector populations are adapted to the environment generally remains unknown. Despite low population structure and high gene flow in Aedes aegypti mosquitoes across Panama, excepting the province of Bocas del Toro, we identified 128 candidate SNPs, clustered within 17 genes, which show a strong genomic signal of local environmental adaptation. This putatively adaptive variation occurred across fine geographical scales with the composition and frequency of candidate adaptive loci differing between populations in wet tropical environments along the Caribbean coast and dry tropical conditions typical of the Pacific coast. Temperature and vegetation were important predictors of adaptive genomic variation in Ae. aegypti with several potential areas of local adaptation identified. Our study lays the foundations of future work to understand whether environmental adaptation in Ae. aegypti impacts the arboviral disease landscape and whether this could either aid or hinder efforts of population control.
    Keywords:  Aedes mosquitoes; Panama; arboviral disease landscape; environmental association analysis; hybridization capture‐based target enrichment; local adaptation
  12. J Exp Biol. 2021 May 15. pii: jeb242231. [Epub ahead of print]224(10):
      Genes known to affect circadian rhythms (i.e. 'clock genes') also influence the photoperiodic induction of overwintering reproductive diapause in the northern house mosquito, Culex pipiens f. pipiens. This suggests that molecular changes in one or more clock genes could contribute to the inability to diapause in a second form of this mosquito, Culex pipiens f. molestus. Temperate populations of Cx. pipiens f. molestus inhabit underground locations generally devoid of predictable photoperiods. For this reason, there could be limited fitness consequences if the hypothesized molecular changes to its clock genes also eliminated this mosquito's ability to regulate circadian rhythms in response to photoperiod variation. Here, we demonstrate that in contrast to this prediction, underground derived Cx. pipiens f. molestus retain exogenously influenceable circadian rhythms. Nonetheless, our genetic analyses indicate that the gene Helicase domino (dom) has a nine-nucleotide, in-frame deletion specific to Cx. pipiens f. molestus. Previous work has shown that splice variants in this gene differentially influence circadian behavior in Drosophila melanogaster. We also find derived, non-synonymous single nucleotide polymorphisms (SNPs) in eight genes that may also affect circadian rhythms and/or diapause induction in Cx. pipiens f. molestus. Finally, four putative circadian genes were found to have no quantifiable expression during any examined life stage, suggesting potential regulatory effects. Collectively, our findings indicate that the distinct, but molecularly interconnected life-history traits of diapause induction and circadian rhythms are decoupled in Cx. pipiens f. molestus and suggest this taxon may be a valuable tool for exploring exogenously influenced phenotypes in mosquitoes more broadly.
    Keywords:   Helicase domino ; Clock genes; Culicidae; Diapause; Life-history traits; Photoperiod
  13. J Med Entomol. 2021 May 28. pii: tjab078. [Epub ahead of print]
      The western mosquitofish, Gambusia affinis (Baird & Girard), has been used worldwide for the control of larval mosquitoes for more than 100 yr. We found that the western encephalitis mosquito, Culex tarsalis Coquillett (Diptera: Culicidae), can detect the presence of G. affinis in oviposition sites based on associated chemicals, leading to a decrease in the number of egg rafts laid. Three volatile chemical compounds were identified in the headspace above the water where G. affinis had been held for 24 h. Oviposition bioassays conducted using standards of the volatile compounds identified (dimethyl disulfide [DMDS], dimethyl trisulfide [DMTS], and S-methyl methanethiosulphonate) found that females reduced oviposition only when low concentrations of DMTS were present, but this response was not consistent across all trials and concentrations tested. DMDS, DMTS, and S-methyl methanethiosulphonate are known bacterial metabolic waste products and may be the source of the compounds. Two nonvolatile compounds of interest were found to be present in the Gambusia-exudate water. After tasting Cx. tarsalis were deterred from ovipositing onto Gambusia-treated water from which the bacteria had been removed by filtration, indicating that the kairomone may consist of nonvolatile compound(s). One of the nonvolatile compounds isolated from the Gambusia-treated water has a benzene ring structure similar to that of cholesterol but the structure of the two nonvolatile deterrents remains to be fully characterized. Our research shows that three volatile compounds and two nonvolatile compounds are present in water associated with G. affinis (Poeciliidae: Gambusia) and affect the oviposition behavior of Cx. tarsalis in laboratory bioassays.
    Keywords:  deterrent; mosquito; mosquitofish; semiochemical
  14. J Venom Anim Toxins Incl Trop Dis. 2021 May 17. 27 e20200155
      Infection with vector-borne pathogens starts with the inoculation of these pathogens during blood feeding. In endemic regions, the population is regularly bitten by naive vectors, implicating a permanent stimulation of the immune system by the vector saliva itself (pre-immune context). Comparatively, the number of bites received by exposed individuals from non-infected vectors is much higher than the bites from infected ones. Therefore, vector saliva and the immunological response in the skin may play an important role, so far underestimated, in the establishment of anti-pathogen immunity in endemic areas. Hence, the parasite biology and the disease pathogenesis in "saliva-primed" and "saliva-unprimed" individuals must be different. This integrated view on how the pathogen evolves within the host together with vector salivary components, which are known to be endowed with a variety of pharmacological and immunological properties, must remain the focus of any investigational study dealing with vector-borne diseases. Considering this three-way partnership, the host skin (immune system), the pathogen, and the vector saliva, the approach that consists in the validation of vector saliva as a source of molecular entities with anti-disease vaccine potential has been recently a subject of active and fruitful investigation. As an example, the vaccination with maxadilan, a potent vasodilator peptide extracted from the saliva of the sand fly Lutzomyia longipalpis, was able to protect against infection with various leishmanial parasites. More interestingly, a universal mosquito saliva vaccine that may potentially protect against a range of mosquito-borne infections including malaria, dengue, Zika, chikungunya and yellow fever. In this review, we highlight the key role played by the immunobiology of vector saliva in shaping the outcome of vector-borne diseases and discuss the value of studying diseases in the light of intimate cross talk among the pathogen, the vector saliva, and the host immune mechanisms.
    Keywords:  Arboviruses; Immunomodulation; Parasites; Vaccine; Vector saliva
  15. Front Public Health. 2021 ;9 611152
      The extreme north of Chile presents a subtropical climate permissive of the establishment of potential disease vectors. Anopheles (Ano.) pseudopunctipennis is distributed from the south of the United States to the north of Argentina and Chile, and is one of the main vectors of malaria in Latin America. Malaria was eradicated from Chile in 1945. Nevertheless, the vector persists in river ravines of the Arica and Tarapacá regions. The principal effect of climate change in the north of Chile is temperature increase. Precipitation prediction is not accurate for this region because records were erratic during the last century. The objective of this study was to estimate the current and the projected distribution pattern of this species in Chile, given the potential impact due to climate change. We compiled distributional data for An. (Ano.) pseudopunctipennis and constructed species distribution models to predict the spatial distribution of this species using the MaxEnt algorithm with current and RCP 4.5 and 8.5 scenarios, using environmental and topographic layers. Our models estimated that the current expected range of An. (Ano.) pseudopunctipennis extends continuously from Arica to the north of Antofagasta region. Furthermore, the RCP 4.5 and 8.5 projected scenarios suggested that the range of distribution of An. (Ano.) pseudopunctipennis may increase in longitude, latitude, and altitude limits, enhancing the local extension area by 38 and 101%, respectively, and local presence probability (>0.7), from the northern limit in Arica y Parinacota region (18°S) to the northern Antofagasta region (23°S). This study contributes to geographic and ecologic knowledge about this species in Chile, as it represents the first local study of An. (Ano.) pseudopunctipennis. The information generated in this study can be used to inform decision making regarding vector control and surveillance programs of Latin America. These kinds of studies are very relevant to generate human, animal, and environmental health knowledge contributing to the "One Health" concept.
    Keywords:  Latin America; One health; climate change; malaria; maxent; species distribution model
  16. One Health. 2021 Dec;13 100261
      In recent years, children in Thailand have been infected with zoonotic Brugia pahangi. However, the local environment of rubber or oil palm plantations, which would increase their exposure to risk factors of the infection due to mosquito transmission, is unclear. The present study first sought to determine the extent to which variations in the local landscape, such as the elevated versus low-lying ecotope of rubber or oil palm plantations, in a 2-km radius of the geographically defined landscape in a rural area of Suratthani, Southern Thailand could influence the abundance of Armigeres subalbatus and its susceptibility to zoonotic filarial parasite infections compared to Mansonia, Aedes, and Culex, and Coquillettidia. Thereafter, the filarial larvae found in the infected mosquitoes were molecularly investigated. Ar. subalbatus plantation ecotype was not only found to outnumber the local mosquitoes, but was identified as the predominant species that adapted well to the elevated ecotopes of the rubber or oil palm plantations, which existed at altitudes of 60-80 m. The overall rate of zoonotic filarial parasite infections (L1, L2, or L3 larvae) of Ar. subalbatus was 2.5% (95% CI, -0.2 to 4.1), with an average L3 load of 2.3 larvae per infected Ar. subalbatus (95% CI, -0.6 to 13.0); this is because the infections were found to be concentrated in the elevated ecotopes alone. Based on filarial orthologous β-tubulin gene-specific touchup-nested PCR and sequence analysis using 30 L3 larva clones as representatives of 9 Ar. subalbatus infectious pools, Ar. subalbatus either carried B. pahangi or Dirofilaria immitis, or both species. Such findings suggest that Ar. subalbatus might have played an imperative role in the transmission of B. pahangi in the plantation areas infested with Ar. subalbatus.
    Keywords:  Armigeres subalbatus; Brugia pahangi; Filarial β-tubulin genes; Local landscape variation; Plantation ecotype; Touchup-nested PCR
  17. Parasite. 2021 ;28 45
      The invasive mosquito Aedes japonicus japonicus (Theobald, 1901) settled in 2013 in the Alsace region, in the northeast of France. In this temperate area, some mosquito species use diapause to survive cold winter temperatures and thereby foster settlement and dispersal. This study reports diapause and its seasonality in a field population of Ae. japonicus in the northeast of France. For two years, eggs were collected from May to the beginning of November. They were most abundant in summer and became sparse in late October. Diapause eggs were determined by the presence of a fully developed embryo in unhatched eggs after repeated immersions. Our study showed effective diapause of Ae. japonicus in this part of France. At the start of the egg-laying period (week 20), we found up to 10% of eggs under diapause, and this rate reached 100% in October. The 50% cut-off of diapause incidence was determined by the end of summer, leading to an average calculated maternal critical photoperiod of 13 h 23 min. Interestingly, diapause was shown to occur in part of the eggs even at the earliest period of the two seasons, i.e. in May of each year. Even though we observed that the size of eggs was positively correlated with diapause incidence, morphology cannot be used as the unique predictive indicator of diapause status due to overlapping measurements between diapausing and non-diapausing eggs. This study provides new knowledge on diapause characterisation and invasive traits of Ae. japonicus.
    Keywords:  Aedes japonicus japonicus; Diapause; East Asian bush mosquito; Egg; France; Morphology
  18. Commun Biol. 2021 May 26. 4(1): 630
      Anopheles coluzzii is a major malaria vector throughout its distribution in west-central Africa. Here we present a whole-genome study of 142 specimens from nine countries in continental Africa and three islands in the Gulf of Guinea. This sample set covers a large part of this species' geographic range. Our population genomic analyses included a description of the structure of mainland populations, island populations, and connectivity between them. Three genetic clusters are identified among mainland populations and genetic distances (FST) fits an isolation-by-distance model. Genomic analyses are applied to estimate the demographic history and ancestry for each island. Taken together with the unique biogeography and history of human occupation for each island, they present a coherent explanation underlying levels of genetic isolation between mainland and island populations. We discuss the relationship of our findings to the suitability of São Tomé and Príncipe islands as candidate sites for potential field trials of genetic-based malaria control strategies.