bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒08‒02
28 papers selected by
Richard Halfpenny
Staffordshire University

  1. J Vis Exp. 2020 Jul 03.
    Tripathi AK, Mlambo G, Kanatani S, Sinnis P, Dimopoulos G.
      Malaria remains one of the most important public health problems, causing significant morbidity and mortality. Malaria is a mosquito borne disease transmitted through an infectious bite from the female Anopheles mosquito. Malaria control will eventually rely on a multitude of approaches, which includes ways to block transmission to, through and from mosquitoes. To study mosquito stages of malaria parasites in the laboratory, we have optimized a protocol to culture highly infectious Plasmodium falciparum gametocytes, a parasite stage required for transmission from the human host to the mosquito vector. P. falciparum gametocytes mature through five morphologically distinct steps, which takes approximately 1-2 weeks. Gametocyte culture described in this protocol is completed in 15 days and are infectious to mosquitoes from days 15-18. These protocols were developed to maintain a continuous cycle of infection competent gametocytes and to maintain uninterrupted supply of mosquito stages of the parasite. Here, we describe the methodology of gametocyte culture and how to infect mosquitoes with these parasites using glass membrane feeders.
  2. PLoS Negl Trop Dis. 2020 Jul 27. 14(7): e0008490
    Francis S, Campbell T, McKenzie S, Wright D, Crawford J, Hamilton T, Huntley-Jones S, Spence S, Belemvire A, Alavi K, Torres Gutierrez C.
      Owing to the increased reports in Aedes-borne diseases in the Caribbean and Latin America, the United States Agency for International Development assisted the Jamaican Ministry of Health and Wellness in conducting insecticide susceptibility tests on Aedes aegypti populations. Sentinel sites were established in seven parishes of Jamaica (St. Catherine, Kingston and St. Andrew, St. Thomas, Portland, St. Mary and St. Ann) and Aedes aegypti eggs were collected, reared to adults per collected population and their susceptibility to varying pyrethroids and organophosphates were tested using the World Health Organization paper bioassays for these insecticides. The Centers for Disease Control and Prevention bottle bioassay was used to assess susceptibility to the carbamate, bendiocarb. The voltage gated sodium channel gene mutations V1016I and I1011V, normally associated with pyrethroid resistance, were also analysed. The results showed that Aedes aegypti collected from all parishes exhibited resistance to pyrethroids at the following concentrations, permethrin 0.25-2.5%; deltamethrin 0.03-0.15%; lambda-cyhalothrin 0.03-0.3%; and etofenprox 0.5-2.5%. The insecticide deltamethrin at concentration 0.3% was the only pyrethroid tested that resulted in high mortality, 94.9 ± 0.34% knockdown within 1 hour of exposure and 98.95 ± 0.01% mortality (p <0.01) at 24 hours post exposure. The frequency of the voltage gated sodium channel gene mutation V1016I was high in the tested population, possibly accounting for the reduced sensitivity to pyrethroids. Organophosphate resistance was also observed in all populations tested. Mortality rates for 0.8% Malathion was 0.8 ± 0.02-60.68 ± 0.01% after 24 hour and 0.00-47.10 ± 0.09%, for pirimiphos-methyl 0.21%. Bendiocarb applied as 12.5 μg/ bottle resulted in mortality rates of 76.25 ± 4.30-100 ± 0.00% after 30 minutes of exposure. The results showed that Ae. aegypti from the seven parishes analysed demonstrated resistance to the insecticides tested. Deltamethrin and bendiocarb at concentrations 0.3% and 12.5μg respectively, were considered most effective, causing high mortality in the local populations. Routine monitoring and evaluations of Ae. aegypti populations from the included parishes are recommended. Additionally, the study results represent the most comprehensive testing to date with local Aedes aegypti populations distributed across different parishes of Jamaica and should be useful to guide national and sub national strategies for vector control and surveillance.
  3. Sci Rep. 2020 Jul 31. 10(1): 12925
    Wilke ABB, Vasquez C, Carvajal A, Medina J, Chase C, Cardenas G, Mutebi JP, Petrie WD, Beier JC.
      Aedes aegypti is the main vector of dengue, Zika, chikungunya, and yellow fever viruses. Controlling populations of vector mosquito species in urban environments is a major challenge and being able to determine what aquatic habitats should be prioritized for controlling Ae. aegypti populations is key to the development of more effective mosquito control strategies. Therefore, our objective was to leverage on the Miami-Dade County, Florida immature mosquito surveillance system based on requested by citizen complaints through 311 calls to determine what are the most important aquatic habitats in the proliferation of Ae. aegypti in Miami. We used a tobit model for Ae. aegypti larvae and pupae count data, type and count of aquatic habitats, and daily rainfall. Our results revealed that storm drains had 45% lower percentage of Ae. aegypti larvae over the total of larvae and pupae adjusted for daily rainfall when compared to tires, followed by bromeliads with 33% and garbage cans with 17%. These results are indicating that storm drains, bromeliads and garbage cans had significantly more pupae in relation to larvae when compared to tires, traditionally know as productive aquatic habitats for Ae. aegypti. Ultimately, the methodology and results from this study can be used by mosquito control agencies to identify habitats that should be prioritized in mosquito management and control actions, as well as to guide and improve policies and increase community awareness and engagement. Moreover, by targeting the most productive aquatic habitats this approach will allow the development of critical emergency outbreak responses by directing the control response efforts to the most productive aquatic habitats.
  4. Parasit Vectors. 2020 Jul 31. 13(1): 392
    Tambwe MM, Moore SJ, Chilumba H, Swai JK, Moore JD, Stica C, Saddler A.
      BACKGROUND: Spatial repellents that drive mosquitoes away from treated areas, and odour-baited traps, that attract and kill mosquitoes, can be combined and work synergistically in a push-pull system. Push-pull systems have been shown to reduce house entry and outdoor biting rates of malaria vectors and so have the potential to control other outdoor biting mosquitoes such as Aedes aegypti that transmit arboviral diseases. In this study, semi-field experiments were conducted to evaluate whether a push-pull system could be used to reduce bites from Aedes mosquitoes.METHODS: The push and pull under investigation consisted of two freestanding transfluthrin passive emanators (FTPE) and a BG sentinel trap (BGS) respectively. The FTPE contained hessian strips treated with 5.25 g of transfluthrin active ingredient. The efficacies of FTPE and BGS alone and in combination were evaluated by human landing catch in a large semi-field system in Tanzania. We also investigated the protection of FTPE over six months. The data were analyzed using generalized linear mixed models with binomial distribution.
    RESULTS: Two FTPE had a protective efficacy (PE) of 61.2% (95% confidence interval (CI): 52.2-69.9%) against the human landing of Ae. aegypti. The BGS did not significantly reduce mosquito landings; the PE was 2.1% (95% CI: -2.9-7.2%). The push-pull provided a PE of 64.5% (95% CI: 59.1-69.9%). However, there was no significant difference in the PE between the push-pull and the two FTPE against Ae. aegypti (P = 0.30). The FTPE offered significant protection against Ae. aegypti at month three, with a PE of 46.4% (95% CI: 41.1-51.8%), but not at six months with a PE of 2.2% (95% CI: -9.0-14.0%).
    CONCLUSIONS: The PE of the FTPE and the full push-pull are similar, indicative that bite prevention is primarily due to the activity of the FTPE. While these results are encouraging for the FTPE, further work is needed for a push-pull system to be recommended for Ae. aegypti control. The three-month protection against Ae. aegypti bites suggests that FTPE would be a useful additional control tool during dengue outbreaks, that does not require regular user compliance.
    Keywords:  Aedes aegypti; BG-sentinel trap; FTPE; Odor-baited trap; Push-pull; Spatial repellent; Transfluthrin
  5. PLoS Pathog. 2020 Jul 29. 16(7): e1008410
    Fraser JE, O'Donnell TB, Duyvestyn JM, O'Neill SL, Simmons CP, Flores HA.
      The bacterial endosymbiont Wolbachia is a biocontrol tool that inhibits the ability of the Aedes aegypti mosquito to transmit positive-sense RNA viruses such as dengue and Zika. Growing evidence indicates that when Wolbachia strains wMel or wAlbB are introduced into local mosquito populations, human dengue incidence is reduced. Despite the success of this novel intervention, we still do not fully understand how Wolbachia protects mosquitoes from viral infection. Here, we demonstrate that the Wolbachia strain wPip does not inhibit virus infection in Ae. aegypti. We have leveraged this novel finding, and a panel of Ae. aegypti lines carrying virus-inhibitory (wMel and wAlbB) and non-inhibitory (wPip) strains in a common genetic background, to rigorously test a number of hypotheses about the mechanism of Wolbachia-mediated virus inhibition. We demonstrate that, contrary to previous suggestions, there is no association between a strain's ability to inhibit dengue infection in the mosquito and either its typical density in the midgut or salivary glands, or the degree to which it elevates innate immune response pathways in the mosquito. These findings, and the experimental platform provided by this panel of genetically comparable mosquito lines, clear the way for future investigations to define how Wolbachia prevents Ae. aegypti from transmitting viruses.
  6. Insect Sci. 2020 Jul 29.
    Zhou TF, Lai ZT, Liu S, Zhou JY, Liu Y, Wu Y, Xu Y, Wu K, Gu JB, Cheng G, Chen XG.
      Zika virus disease is caused by Zika virus infection, as transmitted by Aedes spp. mosquitoes. Many of the Zika virus strains isolated from patients display different pathogenicities toward humans. The vector mosquitoes for Zika virus are mainly of the Aedes genus, especially Aedes aegypti and Aedes albopictus. However, susceptibility and interactions between Aedes spp. mosquitoes and Zika viruses remain unclear. In this study, we chose two Zika virus strains (FSS13025 and PRVABC59) with different abilities to infect the primary vector mosquitoes Ae. aegypti and Ae. albopictus. The transcriptomes and small RNA profiles of infected and uninfected mosquitoes were comparatively analyzed, and differentially expressed genes were functionally examined using RNAi. According to the results, the susceptibility of PRVABC59 was higher than that of FSS13025 in Aedes vector mosquitoes, and Ae. aegypti was more susceptible to Zika virus than was Ae. albopictus. For PRVABC59 infection, specific differential expression profiles correlated with Ae. aegypti and Ae. albopictus, and susceptibility was significantly affected when three targeted genes were successfully knocked down. Compared with PRVABC59, infection of Ae. albopictus with FSS13025 generated more 21-nt virus small interference RNA. It can be concluded that the susceptibility of vector Aedes spp. mosquitoes to Zika viruses varies and that the interactions between mosquitoes and ZIKV correlate with susceptibility.
    Keywords:  Aedes aegypti; Aedes albopictus; RNA-Seq; RNAi; Zika virus; susceptibility
  7. Front Microbiol. 2020 ;11 1456
    Ford SA, Albert I, Allen SL, Chenoweth SF, Jones M, Koh C, Sebastian A, Sigle LT, McGraw EA.
      Wolbachia is an intracellular bacterium that blocks virus replication in insects and has been introduced into the mosquito, Aedes aegypti for the biocontrol of arboviruses including dengue, Zika, and chikungunya. Despite ongoing research, the mechanism of Wolbachia-mediated virus blocking remains unclear. We recently used experimental evolution to reveal that Wolbachia-mediated dengue blocking could be selected upon in the A. aegypti host and showed evidence that strong levels of blocking could be maintained by natural selection. In this study, we investigate the genetic variation associated with blocking and use these analyses to generate testable hypotheses surrounding the mechanism of Wolbachia-mediated dengue blocking. From our results, we hypothesize that Wolbachia may block virus replication by increasing the regeneration rate of mosquito cells via the Notch signaling pathway. We also propose that Wolbachia modulates the host's transcriptional pausing pathway either to prime the host's anti-viral response or to directly inhibit viral replication.
    Keywords:  Aedes aegypti; Wolbachia pipientis; disease control; evolution; genetic variation
  8. Sci Rep. 2020 Jul 29. 10(1): 12731
    Lv RC, Zhu C-, Wang CH, Ai LL, Lv H, Zhang B, Li CM, An J, Wang PG, Hu D, Tan XZ, Yang L, Zhou HN, Tan WL.
      Dengue fever is a mosquito-borne disease caused by the dengue virus. Aedes aegypti (Ae. Aegypti) is considered the primary vector of Dengue virus transmission in Yunnan Province, China. With increased urbanization, Ae. aegypti populations have significantly increased over the last 20 years. Despite all the efforts that were made for controlling the virus transmission, especially on border areas between Yunnan and Laos, Vietnam, and Myanmar (dengue-endemic areas), the epidemic has not yet been eradicated. Thus, further understanding of the genetic diversity, population structure, and invasive strategies of Ae. aegypti populations in the border areas was vital to uncover the vector invasion and distribution dynamic, and essential for controlling the infection. In this study, we analyzed genetic diversity and population structure of eight adult Ae. Aegypti populations collected along the border areas of Yunnan Province in 2017 and 2018. Nine nuclear microsatellite loci and mitochondrial DNA (mtDNA) sequences were used to achieve a better understanding of the genetic diversity and population structure. One hundred and fourteen alleles were found in total. The polymorphic information content value, together with the expected heterozygosity (He) and observed heterozygosity (Ho) values showed high genetic diversity in all mosquito populations. The clustering analysis based on Bayesian algorithm, the UPGMA and DAPC analysis revealed that all the eight Ae. aegypti populations can be divided into three genetic groups. Based on the mtDNA results, all Ae. aegypti individuals were divided into 11 haplotypes. The Ae. aegypti populations in the border areas of Yunnan Province presented with high genetic diversity, which might be ascribed to the continuous incursion of Ae. aegypti.
  9. Parasit Vectors. 2020 Jul 29. 13(1): 376
    da Silva WJ, Pilz-Júnior HL, Heermann R, da Silva OS.
      The control of insects of medical importance, such as Aedes aegypti and Aedes albopictus are still the only effective way to prevent the transmission of diseases, such as dengue, chikungunya and Zika. Their control is performed mainly using chemical products; however, they often have low specificity to non-target organisms, including humans. Also, studies have reported resistance to the most commonly used insecticides, such as the organophosphate and pyrethroids. Biological control is an ecological and sustainable method since it has a slow rate of insect resistance development. Bacterial species of the genera Xenorhabdus and Photorhabdus have been the target of several research groups worldwide, aiming at their use in agricultural, pharmaceutical and industrial products. This review highlights articles referring to the use of Xenorhabdus and Photorhabdus for insects and especially for mosquito control proposing future ways for their biotechnological applicability. Approximately 24 species of Xenorhabdus and five species of Photorhabdus have been described to have insecticidal properties. These studies have shown genes that are capable of encoding low molecular weight proteins, secondary toxin complexes and metabolites with insecticide activities, as well as antibiotic, fungicidal and antiparasitic molecules. In addition, several species of Xenorhabdus and Photorhabdus showed insecticidal properties against mosquitoes. Therefore, these biological agents can be used in new control methods, and must be, urgently considered in short term, in studies and applications, especially in mosquito control.
    Keywords:  Aedes aegypti; Biological control; Entomopathogenic bacteria; Mosquito-borne arboviruses; Photorhabdus luminescens; Xenorhabdus nematophila
  10. Sci Rep. 2020 07 28. 10(1): 12640
    Muñoz ÁG, Chourio X, Rivière-Cinnamond A, Diuk-Wasser MA, Kache PA, Mordecai EA, Harrington L, Thomson MC.
      Aedes-borne diseases, such as dengue and chikungunya, are responsible for more than 50 million infections worldwide every year, with an overall increase of 30-fold in the last 50 years, mainly due to city population growth, more frequent travels and ecological changes. In the United States of America, the vast majority of Aedes-borne infections are imported from endemic regions by travelers, who can become new sources of mosquito infection upon their return home if the exposed population is susceptible to the disease, and if suitable environmental conditions for the mosquitoes and the virus are present. Since the susceptibility of the human population can be determined via periodic monitoring campaigns, the environmental suitability for the presence of mosquitoes and viruses becomes one of the most important pieces of information for decision makers in the health sector. We present a next-generation monitoring and forecasting system for [Formula: see text]-borne diseases' environmental suitability (AeDES) of transmission in the conterminous United States and transboundary regions, using calibrated ento-epidemiological models, climate models and temperature observations. After analyzing the seasonal predictive skill of AeDES, we briefly consider the recent Zika epidemic, and the compound effects of the current Central American dengue outbreak happening during the SARS-CoV-2 pandemic, to illustrate how a combination of tailored deterministic and probabilistic forecasts can inform key prevention and control strategies .
  11. J Invertebr Pathol. 2020 Jul 23. pii: S0022-2011(20)30151-8. [Epub ahead of print] 107445
    Soni M, Khan SA, Bhattacharjee CK, Dutta P.
      Epidemiology of dengue fever has substantially changed over the years with respect to prevalent strains, affected geographical locations and severity of disease. Mosquito vectors show variable response in terms of susceptibility to four different serotypes of dengue virus. Although studies have postulated that, the vectors Ae. aegypti and Ae. albopictus are crucial for transmission of dengue virus, comparative efficacy of these species for viral transmission and tolerance is still enigmatic. In this study, these two vectors were infected orally with four serotypes of the dengue virus viz. DENV-1 to DENV-4 and their co-infection. It was observed that Ae. aegypti harbors multiple serotype infections more efficiently than Ae. albopictus. We suggest that transovarial transmission is of low importance in the epidemiology of the virus due to low infection rates in the filial generation, and also that reduced fecundity and fertility in both vectors after dengue virus infection affect the ecology of the pathogen.
    Keywords:  Aedes aegypti; Aedes albopictus; Dengue serotype; North East India; co-infection; transmission
  12. J Ethnopharmacol. 2020 Jul 27. pii: S0378-8741(20)33005-1. [Epub ahead of print] 113124
    Gou Y, Li Z, Fan R, Guo C, Wang L, Sun H, Li J, Zhou C, Wang C, Wang Y.
      ETHNOPHARMACOLOGICAL RELEVANCE: Dengue is one of the most important pervasive diseases in many regions of the world, including China. There is an urgent need for new repellents, including plant derivatives, due to the resistance, toxicity, and non-degradability of synthetic insecticides. Traditional plant-based remedies may provide potential avenues for developing new strategies.AIMS OF THE STUDY: The aims of this study were to 1) document the traditional mosquitoes repellent plants used by the Dai people of Xishuangbanna, China; 2) screen out new efficient mosquito repellent plants as candidates for further study.
    MATERIALS AND METHODS: During the period August 2016 to July 2017, five field surveys were conducted in 16 villages of Xishuangbanna. A total of 81 informants (44 males and 37 females) were interviewed using semi-structured questions to collect detailed information on the plants they use to prevent mosquito bites. Ten plants with higher popularity and larger resource were collected and extracts were prepared by hydro-distillation or with petroleum ether. Extracts were tested for adult Aedes albopictus repellency using a human-bait cage. Firstly, repellency was determined as the Minimum Effective Dosage (MED) per minute at which 1% of the mosquito bite through the treated cloth. Secondly, five plant extracts with lower MEDs were tested the repellent longevity of different concentrations.
    RESULTS: Eighteen plants were documented as being used in traditional remedies against mosquitoes. The methods for controlling mosquitoes were diverse: direct burning was used for most plants (16 species), followed by smearing (5 species), and placing (5 species). Laboratory analyses confirmed that ten plants did exhibit mosquito repellent activity. Of them, Artemisia indica, Nicotiana tabacum, Blumea balsamifera, Vitex trifolia, and Chromolaena odorata showed good mosquito repellency with MEDs of 0.015, 0.061, 0.090, 0.090, and 0.105 mg/cm2, respectively. The protection rate provided by A. indica is also the highest among five plants. Although it provides complete protection time of only 30 min at 0.45 mg/cm2 concentration, its repellency within 2 h is not significantly different from that of DEET.
    CONCLUSION: Dai villagers in Xishuangbanna have a rich, diverse and scientific knowledge of plant-based mosquito repellents. Laboratory experiments screened out several plants as candidates for mosquito repellents, of which Artemisia indica was the most promising candidate plant.
    Keywords:  Dai people; Ethnobotanical survey; Mosquito; Repellent; Xishuangbanna
  13. PLoS Negl Trop Dis. 2020 Jul;14(7): e0008434
    Cheng YC, Lee FJ, Hsu YT, Slud EV, Hsiung CA, Chen CH, Liao CL, Wen TH, Chang CW, Chang JH, Wu HY, Chang TP, Lin PS, Ho HP, Hung WF, Chou JD, Tsou HH.
      Dengue fever is a viral disease transmitted by mosquitoes. In recent decades, dengue fever has spread throughout the world. In 2014 and 2015, southern Taiwan experienced its most serious dengue outbreak in recent years. Some statistical models have been established in the past, however, these models may not be suitable for predicting huge outbreaks in 2014 and 2015. The control of dengue fever has become the primary task of local health agencies. This study attempts to predict the occurrence of dengue fever in order to achieve the purpose of timely warning. We applied a newly developed autoregressive model (AR model) to assess the association between daily weather variability and daily dengue case number in 2014 and 2015 in Kaohsiung, the largest city in southern Taiwan. This model also contained additional lagged weather predictors, and developed 5-day-ahead and 15-day-ahead predictive models. Our results indicate that numbers of dengue cases in Kaohsiung are associated with humidity and the biting rate (BR). Our model is simple, intuitive and easy to use. The developed model can be embedded in a "real-time" schedule, and the data (at present) can be updated daily or weekly based on the needs of public health workers. In this study, a simple model using only meteorological factors performed well. The proposed real-time forecast model can help health agencies take public health actions to mitigate the influences of the epidemic.
  14. Adv Virus Res. 2020 ;pii: S0065-3527(20)30025-7. [Epub ahead of print]107 223-246
    Platt DJ, Miner JJ.
      Zika virus (ZIKV) is a mosquito-borne virus of the flavivirus genus in the Flaviviridae family. Flaviviruses are single-stranded, positive-sense RNA viruses that have been responsible for numerous human epidemics. Notable flaviviruses include mosquito-borne viruses such as yellow fever virus (YFV), Dengue virus (DENV), West Nile virus (WNV), Japanese encephalitis virus (JEV), as well as tick-borne viruses including Powassan virus (POWV) and tick-borne encephalitis virus (TBEV). Despite having been relatively obscure until the past decade, ZIKV has become a major global health concern, and is a topic of active research following multiple outbreaks across the globe. Here, we discuss ZIKV pathogenesis and the associated immunopathology, as well as advances in research, therapies, and vaccines developed using models of ZIKV pathogenesis.
    Keywords:  Congenital abnormalities; Flavivirus; Guillain-Barré syndrome; Immunopathology; Viral infection; Viral pathogenesis; Zika virus
  15. BMC Microbiol. 2020 Jul 28. 20(1): 225
    Abílio AP, Silva M, Kampango A, Narciso I, Gudo ES, das Neves LCB, Sidat M, Fafetine JM, de Almeida APG, Parreira R.
      BACKGROUND: Mosquito-borne diseases involving arboviruses represent expanding threats to sub-Saharan Africa imposing as considerable burden to human and veterinary public health. In Mozambique over one hundred species of potential arbovirus mosquito vectors have been identified, although their precise role in maintaining such viruses in circulation in the country remains to be elucidated. The aim of this study was to screen for the presence of flaviviruses, alphaviruses and bunyaviruses in mosquitoes from different regions of Mozambique.RESULTS: Our survey analyzed 14,519 mosquitoes, and the results obtained revealed genetically distinct insect-specific flaviviruses, detected in multiple species of mosquitoes from different genera. In addition, smaller flavivirus-like NS5 sequences, frequently detected in Mansonia seemed to correspond to defective viral sequences, present as viral DNA forms. Furthermore, three lineages of putative members of the Phenuiviridae family were also detected, two of which apparently corresponding to novel viral genetic lineages.
    CONCLUSION: This study reports for the first-time novel insect-specific flaviviruses and novel phenuiviruses, as well as frequent flavivirus-like viral DNA forms in several widely known vector species. This unique work represents recent investigation of virus screening conducted in mosquitoes from Mozambique and an important contribution to inform the establishment of a vector control program for arbovirus in the country and in the region.
    Keywords:  Bunyaviruses; Flaviviruses; Mosquitoes; Mozambique; Phylogenetic analysis; Viral DNA forms
  16. J Therm Biol. 2020 Jul;pii: S0306-4565(20)30150-9. [Epub ahead of print]91 102637
    Verhulst NO, Brendle A, Blanckenhorn WU, Mathis A.
      Temperature is an important determinant affecting the capacity of disease vectors like mosquitoes (Culicidae) to transmit disease agents. Although the impact of temperature on vector-borne disease dynamics has been studied intensively, the actual temperature encountered by the vector in a heterogeneous landscape is rarely taken into account. If disease vectors have temperature preferences and therefore select specific microhabitats, this would substantially influence key life history traits that determine transmission intensity. The thermal preferences of subtropical Aedes aegypti and temperate Ae. japonicus mosquitoes were investigated in a temperature gradient set-up consisting of a Plexiglas box on top of an aluminium plate on two thermal regulators. Blood-fed (one day after feeding) and unfed (non-blood-fed) mosquitoes were released in small (15-20 °C, 20-25 °C, 25-30 °C) and large (15-30 °C, 30-45 °C) temperature gradients to assess their thermal preferences after 15 min. Additionally, the effect of humidity was investigated in a two-choice chamber setup. Both mosquito species avoided higher temperatures, pronouncedly dangerously high temperatures in the 30-45 °C gradient. At lower temperatures, blood-fed mosquitoes preferred the cooler sides of the 20-25 °C and 25-30 °C gradient, which were all below their rearing temperature. In the lowest gradient of 15-20 °C, no preferences were found. The thermal preference of unfed mosquitoes was similar to that of the blood-fed mosquitoes. No humidity preference or effect of humidity on temperature preferences was observed within the tested range (40-90%). The set-up allows for assessing the thermal preference of mosquitoes under controlled conditions. The observed preference of mosquitoes for cooler temperatures would increase their longevity and slow down pathogen development. If similar microhabitat selection is observed in the field, vector borne disease models should be adjusted accordingly.
    Keywords:  Behaviour; Culicidae; Humidity; Microclimate; Temperature preference; Vector
  17. Travel Med Infect Dis. 2020 Jul 23. pii: S1477-8939(20)30227-1. [Epub ahead of print] 101748
    Fouque F, Guidi V, Lazzaro M, Ravasi D, Martinetti-Lucchini G, Merlani G, Tonolla M, Flacio E.
      BACKGROUND: The Preparedness Plan for Surveillance and Interventions on Emerging Vector-Borne Diseases (VBDs) in Southern Switzerland outlines the strategy for preventing and managing potential outbreaks, as well as the surveillance and control activities with a specific focus on Aedes-borne diseases transmitted by Aedes albopictus mosquitoes. The objective of the plan is to provide Public Health Authorities with a framework of preventive and control measures according to the situation and level of epidemic risks.MATERIAL AND METHODS: The plan is divided into various phases representing the different steps for all potential situations, ranging from no vectors and no transmission risk to epidemic levels with multiple autochthonous/local cases of hospitalization (and deaths) until the end of the epidemic. An algorithm presents how decisions are taken to move from one phase of the plan to another, with detailed activities for different partners and strategies for each specific phase.
    RESULTS: The different phases of the plan include activities on disease surveillance and clinical case management, on vector surveillance and control, communication and coordination of activities. The plan is divided into 5 phases of activities and decision levels. From phase 0 (no cases) to phase 1 (low number of local cases, less than 5), phase 2 (small outbreak with more than 5 local cases), phase 3 (epidemic) and phase 4 (return to no more cases).
    CONCLUSION: The plan has been approved by the cantonal authorities and will be submitted to federal authorities. The required implementation tests will begin shortly.
    Keywords:  Aedes albopictus; Arboviruses; Canton Ticino; Emergency; Preparedness plan
  18. Trans R Soc Trop Med Hyg. 2020 Jul 28. pii: traa058. [Epub ahead of print]
    Beranek MD, Quaglia AI, Peralta GC, Flores FS, Stein M, Diaz LA, Almirón WR, Contigiani MS.
      BACKGROUND: St. Louis encephalitis virus (SLEV) is endemic and autochthonous on the American continent. Culex pipiens quinquefasciatus is a vector of SLEV; however, Culex interfor and Culex saltanensis have also been found to be naturally infected with SLEV. The aim of this study was to determine the vector competence of C. interfor and C. saltanensis for SLEV from Argentina compared with C. p. quinquefasciatus. Culex genus is Cx.?METHODS: Female of the Culex species were orally infected by feeding on viraemic chicks that had been inoculated with SLEV. Abdomens, legs and saliva blood-fed mosquitoes were analysed by viral plaque assay.
    RESULTS: Mosquitoes were susceptible to orally acquired infection, dissemination and transmission of SLEV in the saliva.
    CONCLUSIONS: Our results demonstrate that C. saltanensis and C. interfor are susceptible to SLEV and competent for its transmission.
    Keywords:   Flavivirus ; Argentina; Culicidae; arbovirus; infectious diseases; vector competence
  19. Infect Dis Poverty. 2020 Jul 31. 9(1): 107
    Flaibani N, Pérez AA, Barbero IM, Burroni NE.
      BACKGROUND: As no globally accepted dengue vaccines or specific antiviral therapies are currently available, controlling breeding sites of Aedes aegypti is a target to prevent dengue outbreaks. The present study aimed to characterize outdoor artificial breeding sites in urban households using an exhaustive classification system.METHODS: A cross-sectional entomological survey was carried out in Colón city, Entre Ríos, Argentina, using a two-stage stratified sampling design during March and April 2014. The city was stratified given the degree of urbanization of each block, and blocks and households were randomly selected. All outdoor containers with water were inspected, and the presence of immature mosquitoes was recorded. Containers were classified according to physical, functional, and location attributes. Generalized linear mixed models were applied to take into account the aggregated nature of the data (containers in houses and houses in blocks).
    RESULTS: Overall, 207 houses were inspected. Out of 522 containers with water, 25% had immatures of Ae. aegypti (7336). In adjusted models, the abundance of immatures was higher in containers with increasing opening surface and volume, without roof cover, exposed to shadow, out of use or with functions related to gardening activities, household chores, water storage, or construction. At block level, immatures abundance was positively associated with the degree of urbanization.
    CONCLUSIONS: We detected high immatures abundance in containers associated with water utilization. This suggests that containers involved in these activities, whether directly (e.g., water storage) or indirectly (e.g., incomplete water drainage in the last use), are susceptible to present a high immature abundance. Although our results indicate the importance of the type of use over the type of container, we encourage the use of both classification criteria for artificial breeding sites of mosquitoes, mainly because these are complementary. Additionally, generalized linear mixed models allowed us to analyse predictor variables at different scales (container/house/block) and consider the lack of independence between observations. An exhaustive analysis of artificial breeding sites that use this analytical methodology can lead to new information that could help designing more appropriate tools for dengue surveillance and control.
    Keywords:  Containers; Immature mosquitoes; Vectors
  20. PLoS One. 2020 ;15(7): e0235430
    Fernando HSD, Hapugoda M, Perera R, Black Iv WC, De Silva BGDNK.
      Phylogeographic relationships among global collections of the mosquito Aedes aegypti were evaluated using the mitochondrial Cytochrome C Oxidase 1 (CO1) and NADH dehydrogenase subunit 4 (ND4) genes including new sequences from Sri Lanka. Phylogeographic analysis estimated that Ae. aegypti arose as a species ~614 thousand years ago (kya) in the late Pleistocene. At 545 kya an "early" East African clade arose that continued to differentiate in East Africa, and eventually gave rise to three lineages one of which is distributed throughout all tropical and subtropical regions, a second that contains Southeast Asian/Sri Lankan mosquitoes and a third that contains mostly New World mosquitoes. West African collections were not represented in this early clade. The late clade continued to differentiate throughout Africa and gave rise to a lineage that spread globally. The most recent branches of the late clade are represented by South-East Asia and India/Pakistan collections. Analysis of migration rates suggests abundant gene flow between India/Pakistan and the rest of the world with the exception of Africa.
  21. Parasit Vectors. 2020 Jul 29. 13(1): 383
    Shirozu T, Soga A, Fukumoto S.
      BACKGROUND: Dirofilaria immitis is a parasitic nematode transmitted by mosquitoes and the cause of heartworm disease in dogs and dirofilariasis in humans and other mammals. The parasite is endemic worldwide. Vector stage research requires a reliable supply of D. immitis microfilariae (mf). It is believed that cryopreserved mf would retain viability and provide a powerful tool for vector stage research. However, reports on cryopreservation of D. immitis mf are limited. Therefore, this study aimed to validate commercial cryopreservation media to establish a practical, convenient and reproducible storage procedure for D. immitis mf.METHODS: Six different commercially available cryopreservation media were compared with the traditional polyvinylpyrrolidone-dimethyl sulfoxide (PVP-DMSO) preservation solution. In vitro viability of purified D. immitis mf and mf-infected total blood was analyzed using a motility assay and propidium iodide staining. In vivo infectivity of Aedes aegypti mosquitoes with cryopreserved mf was assessed using a mosquito survival test and quantifying the number of third-stage larvae (L3) after 13 days post-infection.
    RESULTS: Purified mf cryopreserved in CultureSure showed the best viability when compared to mf cryopreserved in the remaining five commercially available media and PVP-DMSO. Viability of mf in mf-infected total blood cryopreserved in CultureSure varied with the ratio of infected blood to CultureSure. Optimum results were obtained with 200 µl mf-infected blood:800 µl CultureSure. CultureSure was also the optimum medium for cryopreserving mf prior to infectivity of A. aegypti. The number of L3 was approximately the same for CultureSure cryopreserved mf (3× concentrated solution) and non-cryopreserved fresh mf.
    CONCLUSIONS: CultureSure is an optimal commercial cryopreservation solution for the storage of D. immitis purified mf, mf-infected total blood, and mf used for in vivo mosquito experiments. Furthermore, this study describes an easy preservation method for clinical D. immitis-infected blood samples facilitating vector stage studies, as well as the study of macrocyclic lactone resistance in heartworms and the education of veterinarians.
    Keywords:  Aedes aegypti; Cryopreservation media; CultureSure; Dirofilaria immitis; Heartworm disease; Microfilariae; Parasitic nematode
  22. Insect Mol Biol. 2020 Jul 26.
    Huff RM, Pitts RJ.
      Many mosquito behaviors that are critical for survival and reproduction depend upon timely responses to chemical cues. Of interest are the effects of volatile organic compounds like carboxylic acids (CAs) that are released by potential blood meal hosts. Short chain CAs are among the primary attractants for host-seeking females and influence host selection in vector species. Although the behavioral relevance of CA's has been established, less is known about the molecular receptive events that evoke responses to specific compounds, with the Ir family of chemoreceptors being broadly implicated in their detection. In this study, we demonstrate that Or orthologs from two vector species, Aedes aegypti (L.) and Aedes albopictus (Skuse), are selectively activated by straight chain carboxylic acids and that these responses are attenuated by the commercial insect repellant N,N-Diethyl-meta-toluamide. Our results suggest that multiple chemoreceptors, representing diverse families, are able to mediate molecular responses to CAs and may therefore underlie important behaviors that directly impact disease-transmission cycles. This article is protected by copyright. All rights reserved.
    Keywords:  Aedes aegypti; Aedes albopictus; DEET; carboxylic acid; odorant receptor; olfaction
  23. Acta Trop. 2020 Jul 28. pii: S0001-706X(20)30857-3. [Epub ahead of print] 105647
    van Eijk AM, Choubey S, Barla P, Haque MA, Nandini P, Acharya S, Sullivan SA, Mohanty S, Satpathi S, Carlton JM.
      To characterize malaria and assist in prevention efforts, we conducted a series of epidemiological studies in Sundargarh district, India, as part of an NIH-funded International Center of Excellence for Malaria Research. In a published survey around Rourkela in 2013-2014 (N=1307), malaria prevalence was found to be 8.3%. Using these data, villages were divided into low (<2%), medium (2-10%) and high (>10%) malaria prevalence, and risk factors assessed by type of village. In the six low malaria villages, four persons were positive by PCR; in the four medium malaria villages, prevalence was 7% (35 infections, 7 P. vivax); and in the three high malaria villages, prevalence was 21% (62 infections, 10 P. vivax and 5 mixed with P. vivax and P. falciparum). A total of 30.6% infections were submicroscopic and 40.6% were asymptomatic. Our analyses showed that the rainy season and male gender were risk factors for malaria; in high malaria villages, young age was an additional risk factor, and indoor and outdoor spraying was protective compared to no spraying. We undertook a subsequent behavioral survey in four of the medium and high malaria villages in 2017 to investigate the behavioral aspects of malaria risk. Among 500 participants in 237 households, adult men (15+ years) were more likely to be outside in the evening (34.5% vs. 7.9% among adult women 15+ years and 0.7% among children, p<0.001), or to sleep outside (7.5% vs. 0.5% and 0%, respectively, p<0.001). Although women were more likely to get up before 6 a.m. (86.6%, vs. 70.5% among men, 50.7% among children, p<0.001), men were more likely to be outside in the early morning (77.6% among men, 11.2% among women, and 11.1% among children, p<0.001). More children used insecticide treated nets the previous night (73.4%) than men (45.6%) or women (39.6%), and repellents were used by 29.5% of 234 households (insecticide creams were not used at all). Malaria control and elimination in India will need local approaches, and the promotion of repellent cream use by at-risk groups could be further explored in addition to mass-screen or treat programs in high-risk villages.
    Keywords:  Malaria risk factors; Mosquito control; Plasmodium falciparum; Plasmodium vivax
  24. J Parasitol Res. 2020 ;2020 7438317
    Sidiki NNA, Payne VK, Cedric Y, Nadia NAC.
      Background: Malaria is one of the major public health problems in many tropical developing countries including Cameroon. Impregnated mosquito bed nets are one of the control measures put in place by the WHO and adopted by the Cameroon's Ministry of Public Health to fight against malaria in pregnancy. This study was a population-based cross-sectional study that investigated the level of adherence, respondent's knowledge, altitude, and practices toward malaria prevention and control.Methods: To investigate this, a sample size of 410 pregnant women who were inhabitants of Foumban Subdivision was examined. Data on net ownership versus usage, pregnancy status, and socioeconomic background were collected using a questionnaire. Parasitological tests for malaria parasites were carried out using peripheral blood samples obtained from finger pricks of the pregnant women for the preparation of thick blood smear and RDTs.
    Results: Two hundred and eighteen tested positive (53.4%) with the highest prevalence occurring during the first trimester (79.6%) and in primigravidae (68.8%). Participants believed that mosquito bed nets can protect them against malaria infection. The highest number (81.0%) of the women who had mosquito nets acquired them during antenatal visits. Among those who possessed nets, 42.7% adhered to sleeping under them and few (50%) experienced problems of sweating, discomfort, and heat. Also, the study revealed a high prevalence rate of 63.8% for those who did not use nets during pregnancy as compared to those who owned and used them.
    Conclusion: The findings indicated that increased access to impregnated mosquito bed nets is required to lower the risk of malaria infection amongst pregnant women. The Cameroon government should improve health education to families within the locality and pursue an integrated approach to fight against mosquitoes during the rainy season.
  25. Parasit Vectors. 2020 Jul 29. 13(1): 379
    Davidson JR, Wahid I, Sudirman R, Small ST, Hendershot AL, Baskin RN, Burton TA, Makuru V, Xiao H, Yu X, Troth EV, Olivieri D, Lizarraga S, Hasan H, Arfah A, Yusuf M, Nur N, Syafruddin D, Asih P, Lobo NF.
      BACKGROUND: Understanding local Anopheles species compositions and bionomic traits are vital for an effective malaria vector intervention strategy. Though eight malaria vectors, including species complexes, have been documented across the island of Sulawesi, Indonesia, a comprehensive survey linking morphological and molecular species identification has not been conducted in this global hotspot of biodiversity.RESULTS: Eighteen distinct species of Anopheles were molecularly identified in a 1 km2 area in Karama village, West Mamuju Province, Sulawesi. Known species included An. aconitus, An. karwari, An. peditaeniatus, An. vagus, An. barbirostris, An. tessellatus, An. nigerrimus, An. crawfordi, An. maculatus, An. flavirostris and An. kochi. Of the 18 distinct sequence groups identified through both ribosomal DNA internal transcribed spacer region 2, and mitochondrial DNA cytochrome c oxidase subunit 1 loci, 8 could not be identified to species through comparison to published sequences. The comparison of morphological and molecular identities determined that interpretations of local species compositions for primary and expected species in Karama (An. barbirostris and An. vagus) had the highest rate of accuracy (92.1% and 87.6%, respectively) when compared to molecular analysis. However, the remaining distinct sequences molecularly identified to species were identified correctly by morphological methods less frequently, from 0 to 83%.
    CONCLUSIONS: Karama, Indonesia has a high diversity of Anopheles spp. The unexpected high number of Anopheles species in a small area points to possible complex transmission dynamics and limitations with vector control based on possible varying behaviors and interactions with both humans and interventions. Morphological identification of Anopheles spp. in this study was more accurate for primary and expected species than secondary or unexpected species. Finally, the inability to identify seven sequence groups to species with consensus sequences implies that future studies employing sequencing are required to clarify species compositions in the Nigerrimus Subgroup, among others, as well as their distribution and vector status. Use of molecular methods in conjunction with morphological investigations for analysis of species composition, population dynamics and bionomic characteristics is directly implicated in understanding drivers of malaria transmission, intervention effectiveness, and the pursuit of malaria elimination.
    Keywords:  Anopheles; Indonesia; Malaria vectors; Molecular identification; Sulawesi
  26. Sci Rep. 2020 Jul 28. 10(1): 12569
    Miura K, Swihart BJ, Fay MP, Kumpitak C, Kiattibutr K, Sattabongkot J, Long CA.
      Standard and direct membrane-feeding assays (SMFA and DMFA) are fundamental assays to evaluate efficacy of transmission-blocking intervention (TBI) candidates against Plasmodium falciparum and vivax. To compare different candidates precisely, it is crucial to understand the error range of measured activity, usually expressed as percent inhibition in either oocyst intensity (% transmission reducing activity, %TRA), or in prevalence of infected mosquitoes (% transmission blocking activity, %TBA). To this end, mathematical models have been proposed for P. falciparum SMFA (PfSMFA), but such study for DMFA is limited. In this study, we analyzed P. vivax DMFA (PvDMFA) data from 22,236 mosquitoes tested from 96 independent assays. While the two assays are quite different, a zero-inflated negative binomial (ZINB) model could reasonably explain the PvDMFA results, as it has for PfSMFA. Our simulation studies based on the ZINB model revealed it is better to report %TRA values with a proper error range, rather than observed %TBA both in SMFA and DMFA. Furthermore, the simulations help in designing a better assay and aid in estimating an error range of a %TRA value when the uncertainty is not reported. This study strongly supports future TBI development by providing a rational method to compare different candidates.
  27. Insects. 2020 Jul 24. pii: E468. [Epub ahead of print]11(8):
    Andrade DC, Morais SA, Marteis LS, Gama RA, Freire RCM, Rekowski BS, Ueno HM, La Corte R.
      Mosquito fauna in the northeast semiarid region of Brazil, Caatinga biome, are poorly known. Studies on the diversity are scarce and the few surveys available focus on local fauna. In order to understand the ecological pattern of mosquito's distribution, information available from studies from 2008 to 2015 were gathered. A partitioning framework of the beta diversity, the turnover (βJTU) and nestedness (βJNE) components were used to determine dissimilarity among communities. Eighty-two morphospecies were recorded and 47 of the species were not shared between the areas. The most representative genera were Aedes, Anopheles, Psorophora, Haemagogus, Coquillettidia, and Mansonia, which all include species of medical interest. The communities had high rates of variation, and the mechanism of turnover accounted for the observed diversity pattern. Despite differences in collection methods, the observed dissimilarity may be related to the broad environmental heterogeneity of the biome, the intrinsic relationships of the species with their habitats, and the environmental degradation caused by different types of anthropogenic interference. Considering the mosquito species richness and endemicity, the hypothesis that the Caatinga harbor poor biodiversity is rejected. The spatial variation observed is of particular importance and should be taken into account for the knowledge of Caatinga biodiversity.
    Keywords:  biodiversity; caatinga; culicidae; semiarid; vector ecology