bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒09‒13
twenty-two papers selected by
Richard Halfpenny
Staffordshire University


  1. Parasit Vectors. 2020 Sep 09. 13(1): 460
    Tang Z, Yamada H, Kraupa C, Canic S, Busquets N, Talavera S, Jiolle D, Vreysen MJB, Bouyer J, Abd-Alla AMM.
      BACKGROUND: Mosquitoes are the deadliest animals in the world. Their ability to carry and spread diseases to humans causes millions of deaths every year. Due to the lack of efficient vaccines, the control of mosquito-borne diseases primarily relies on the management of the vector. Traditional control methods are insufficient to control mosquito populations. The sterile insect technique (SIT) is an additional control method that can be combined with other control tactics to suppress specific mosquito populations. The SIT requires the mass-rearing and release of sterile males with the aim to induce sterility in the wild female population. Samples collected from the environment for laboratory colonization, as well as the released males, should be free from mosquito-borne viruses (MBV). Therefore, efficient detection methods with defined detection limits for MBV are required. Although a one-step reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) method was developed to detect arboviruses in human and mosquito samples, its detection limit in mosquito samples has yet to be defined.METHODS: We evaluated the detection sensitivity of one step RT-qPCR for targeted arboviruses in large mosquito pools, using pools of non-infected mosquitoes of various sizes (165, 320 and 1600 mosquitoes) containing one infected mosquito body with defined virus titers of chikungunya virus (CHIKV), usutu virus (USUV), West Nile virus (WNV) and Zika virus (ZIKV).
    RESULTS: CHIK, USUV, ZIKV, and WNV virus were detected in all tested pools using the RT-qPCR assay. Moreover, in the largest mosquito pools (1600 mosquitoes), RT-qPCR was able to detect the targeted viruses using different total RNA quantities (10, 1 and 0.1 ng per reaction) as a template. Correlating the virus titer with the total RNA quantity allowed the prediction of the maximum number of mosquitoes per pool in which the RT-qPCR can theoretically detect the virus infection.
    CONCLUSIONS: Mosquito-borne viruses can be reliably detected by RT-qPCR assay in pools of mosquitoes exceeding 1000 specimens. This will represent an important step to expand pathogen-free colonies for mass-rearing sterile males for programmes that have a SIT component by reducing the time and the manpower needed to conduct this quality control process.
    Keywords:  Arbovirus; Chikungunya virus (CHIKV); Flavivirus; Pool size; RT-qPCR; Usutu virus (USUV); West Nile virus (WNV); Zika virus (ZIKV)
    DOI:  https://doi.org/10.1186/s13071-020-04327-4
  2. J Med Entomol. 2020 Sep 09. pii: tjaa174. [Epub ahead of print]
    Mullens P, Su T, Vong Q, Thieme J, Brown MQ.
      The yellow fever mosquito, Aedes aegypti (Linnaeus, 1762), is the most aggressive invasive mosquito species with worldwide distribution. In addition to being a notorious nuisance species, it can pose significant public health concern because of its ability to transmit various viral pathogens. The first adult capture in the West Valley area of San Bernardino County, CA, occurred in September 2015 in Montclair. A strategic surveillance plan was implemented accordingly by the West Valley Mosquito and Vector Control District to document the infestation. The Biogent Sentinel (BG-2) trap augmented with BG-Lure and carbon dioxide (CO2) was deployed as a routine surveillance tool during 2017-2019. Extensive trapping revealed an expanding infestation, when positive trap nights (TN) increased from 14.2% in 2017 to 23.9% in 2018 and 55.6% in 2019. The average counts/TN increased from 0.65 in 2017 and 0.90 in 2018 to 3.83 in 2019. The cities of Montclair, Chino, and Ontario had much higher infestation than other cities in the district with the highest positive TN of 46.0% in Montclair, and highest average trap count of 3.23/TN in Chino. It was interesting to note that males coincided with females with more profound trend during warmer months of July to October when ratios of males ranged 28.4-35.0%. The BG-2 trap significantly outperformed the CO2 trap and gravid trap. The establishment of this invasive species in semiarid inland Southern California was further confirmed by concurrent larval collections.
    Keywords:   Aedes aegypti ; Biogent Sentinel trap; Culicidae; Diptera; establishment
    DOI:  https://doi.org/10.1093/jme/tjaa174
  3. BMC Public Health. 2020 Sep 11. 20(1): 1385
    Leontsini E, Maloney S, Ramírez M, Rodriguez E, Gurman T, Ballard Sara A, Hunter GC.
      BACKGROUND: In El Salvador, Aedes aegypti mosquitoes transmitting Zika and other arboviruses use water storage containers as important oviposition sites. Promotion of water storage container cleaning is a key element of prevention programs. We explored community perceptions surrounding cleaning practices among pregnant women, male partners of pregnant women, and women likely to become pregnant.METHODS: Researchers conducted 11 focus groups and 12 in-depth interviews which included individual elicitations of Zika prevention measures practiced in the community. Focus group participants rated 18 images depicting Zika-related behaviors according to effectiveness and feasibility in the community context, discussed influencing determinants, voted on community intentions to perform prevention behaviors, and performed washbasin cleaning simulations. In-depth interviews with male partners of pregnant women used projective techniques with images to explore their perceptions on a subset of Zika prevention behaviors.
    RESULTS: General cleaning of the home, to ensure a healthy environment, was a strong community norm. In this context, participants gave water storage container cleaning a high rating, for both its effectiveness and feasibility. Participants were convinced that they cleaned their water storage containers effectively against Zika, but their actual skills were inadequate to destroy Aedes aegypti eggs. A further constraint was the schedule of water availability. Even during pregnancy, male partners rarely cleaned water storage containers because water became available in homes when they were at work. Furthermore, prevailing gender norms did not foster male participation in domestic cleaning activities. Despite these factors, many men were willing to provide substantial support with cleaning when their partners were pregnant, in order to protect their family.
    CONCLUSIONS: Behavior change programs for the prevention of Zika and other arboviruses need to improve community members' mosquito egg destruction skills rather than perpetuate the promotion of non-specific cleaning in and around the home as effective. Egg elimination must be clearly identified as the objective of water storage container maintenance and programs should highlight the effective techniques to achieve this goal. In addition, programs must build the skills of family members who support pregnant women to maintain the frequency of effective egg destruction in all water storage containers of the home.
    Keywords:  Arbovirus prevention; Behavioral determinants; Chikungunya; Community control of Aedes aegypti; Dengue; El Salvador; Mosquito ovicidal technique; Untadita; Water storage containers; Zika
    DOI:  https://doi.org/10.1186/s12889-020-09370-5
  4. Parasit Vectors. 2020 Sep 11. 13(1): 466
    Fongnikin A, Houeto N, Agbevo A, Odjo A, Syme T, N'Guessan R, Ngufor C.
      BACKGROUND: A new generation of IRS insecticides which can provide improved and prolonged control of pyrethroid-resistant malaria vector populations are being developed. Fludora® Fusion is a new IRS insecticide containing a mixture of deltamethrin and clothianidin, a neonicotinoid.METHODS: The efficacy of Fludora® Fusion IRS was evaluated over 11-12 months on concrete and mud substrates in laboratory bioassays and experimental huts against wild free-flying pyrethroid-resistant Anopheles gambiae (sensu lato) in Cové, Benin. A comparison was made with the two active ingredients of the mixture; clothianidin and deltamethrin, applied alone. CDC bottle bioassays were also performed to investigate resistance to clothianidin in the wild vector population.
    RESULTS: Fludora® Fusion induced > 80% laboratory cone bioassay mortality with both susceptible and pyrethroid-resistant An. gambiae (s.l.) for 7-9 months on concrete block substrates and 12 months on mud block substrates. The vector population at the experimental hut site was fully susceptible to clothianidin in CDC bottle bioassays. Overall mortality rates of wild free-flying pyrethroid-resistant An. gambiae (s.l.) entering the experimental huts during the 11-month trial were < 15% with deltamethrin and significantly higher with Fludora® Fusion (69-71%) and clothianidin alone (72-78%). Initial high experimental hut mortality rates with Fludora® Fusion (> 80%) only declined by 50% after 8 months. Monthly in situ wall cone bioassay mortality of susceptible mosquitoes was > 80% for 9-12 months with Fludora® Fusion and clothianidin alone. Fludora® Fusion induced significantly higher levels of early exiting of mosquitoes compared to clothianidin alone (55-60% vs 37-38%, P < 0.05).
    CONCLUSIONS: Indoor residual spraying with Fludora® Fusion induced high and prolonged mortality of wild pyrethroid-resistant malaria vectors for 7-10 months mostly due to the clothianidin component and substantial early exiting of mosquitoes from treated huts due to the pyrethroid component. Fludora® Fusion is an important addition to the current portfolio of IRS insecticides with the potential to significantly reduce transmission of malaria by pyrethroid-resistant mosquito vectors.
    Keywords:  Anopheles; Clothianidin; Cové; Experimental huts; Fludora; Fludora® Fusion; Formulations; IRS block substrates; IRS mixtures; Indoor residual spraying; Malaria vectors; Mixtures; Mosquito control; Neonicotinoids; Pyrethroid resistance; Vector control
    DOI:  https://doi.org/10.1186/s13071-020-04341-6
  5. PLoS Negl Trop Dis. 2020 Sep;14(9): e0008531
    Tallon AK, Lorenzo MG, Moreira LA, Martinez Villegas LE, Hill SR, Ignell R.
      Pathogens may manipulate their human and mosquito hosts to enhance disease transmission. Dengue, caused by four viral serotypes, is the fastest-growing transmissible disease globally resulting in 50-100 million infections annually. Transmission of the disease relies on the interaction between humans and the vector Aedes aegypti and is largely dependent on the odor-mediated host seeking of female mosquitoes. In this study, we use activity monitors to demonstrate that dengue virus-1 affects the locomotion and odor-mediated behavior of Ae. aegypti, reflecting the progression of infection within the mosquito. Mosquitoes 4-6 days post-infection increase locomotion, but do not alter their odor-driven host-seeking response. In contrast, females 14-16 days post-infection are less active, yet more sensitive to human odors as assessed by behavioral and electrophysiological assays. Such an increase in physiological and behavioral sensitivity is reflected by the antennal-specific increase in abundance of neural signaling transcripts in 14 days post-infection females, as determined by transcriptome analysis. This suggests that the sensitivity of the mosquito peripheral olfactory system is altered by the dengue virus by enhancing the overall neural responsiveness of the antenna, rather than the selective regulation of chemosensory-related genes. Our study reveals that dengue virus-1 enhances vector-related behaviors in the early stages post-infection that aid in avoiding predation and increasing spatial exploration. On the other hand, at the later stages of infection, the virus enhances the host-seeking capacity of the vector, thereby increasing the risk of virus transmission. A potential mechanism is discussed.
    DOI:  https://doi.org/10.1371/journal.pntd.0008531
  6. PLoS Negl Trop Dis. 2020 Sep 08. 14(9): e0008527
    Chouin-Carneiro T, David MR, de Bruycker Nogueira F, Dos Santos FB, Lourenço-de-Oliveira R.
      BACKGROUND: Zika virus (ZIKV) emerged in the Pacific Ocean and subsequently caused a dramatic Pan-American epidemic after its first appearance in the Northeast region of Brazil in 2015. The virus is transmitted by Aedes mosquitoes. We evaluated the role of temperature and infectious doses of ZIKV in vector competence of Brazilian populations of Ae. aegypti and Ae. albopictus.METHODOLOGY/PRINCIPAL FINDINGS: Two Ae. aegypti (Rio de Janeiro and Natal) and two Ae. albopictus (Rio de Janeiro and Manaus) populations were orally challenged with five viral doses (102 to 106 PFU / ml) of a ZIKV strain (Asian genotype) isolated in Northeastern Brazil, and incubated for 14 and 21 days in temperatures mimicking the spring-summer (28°C) and winter-autumn (22°C) mean values in Brazil. Detection of viral particles in the body, head and saliva samples was done by plaque assays in cell culture for determining the infection, dissemination and transmission rates, respectively. Compared with 28°C, at 22°C, transmission rates were significantly lower for both Ae. aegypti populations, and Ae. albopictus were not able to transmit the virus. Ae. albopictus showed low transmission rates even when challenged with the highest viral dose, while both Ae. aegypti populations presented higher of infection, dissemination and transmission rates than Ae. albopictus. Ae. aegypti showed higher transmission efficiency when taking virus doses of 105 and 106 PFU/mL following incubation at 28°C; both Ae. aegypti and Ae. albopictus were unable to transmit ZIKV with virus doses of 102 and 103 PFU/mL, regardless the incubation temperature.
    CONCLUSIONS/SIGNIFICANCE: The ingested viral dose and incubation temperature were significant predictors of the proportion of mosquito's biting becoming infectious. Ae. aegypti and Ae. albopictus have the ability to transmit ZIKV when incubated at 28°C. However Brazilian populations of Ae. aegypti exhibit a much higher transmission potential for ZIKV than Ae. albopictus regardless the combination of infection dose and incubation temperature.
    DOI:  https://doi.org/10.1371/journal.pntd.0008527
  7. J Med Entomol. 2020 Sep 11. pii: tjaa182. [Epub ahead of print]
    Su T, Thieme J, Cummings R, Cheng ML, Brown MQ.
      The juvenile hormone analog S-methoprene is the only synthetic biopesticide that is registered with the United States Environmental Protection Agency to control arthropods of economic importance in public health, livestock, pets, urban, and stored products. The high activity, relative target specificity, and benign environmental profile of S-methoprene have been well documented. While the risk of resistance in mosquitoes to S-methoprene is generally low, there is a lack of information regarding cross resistance in S-methoprene-resistant mosquitoes to other pesticides. In this paper, a population of the southern house mosquito Culex quinquefasciatus Say from southern California acquired low levels of resistance to S-methoprene in the field, where the resistance ratios ranged 7.0- to 8.8-fold as compared with a laboratory reference colony. After 30 generations of laboratory selections by S-methoprene when resistance was elevated to 57.4- to 168.3-fold relative to an unselected population, various levels of cross resistance to other commonly used pesticides were revealed in the selected population. Cross resistance to the microbial mosquito larvicide Lysinibacillus sphaericus (Meyer & Neide) (Bacillales: Bacillaceae) was the most profound, amounting to 77.50- to 220.50-fold. The mechanism and potential management tactics toward cross resistance are discussed to preserve the unique value of this synthetic biopesticide.
    Keywords:   Culex quinquefasciatus ; Culicidae; Diptera; S-methoprene; cross resistance
    DOI:  https://doi.org/10.1093/jme/tjaa182
  8. Biomed Res Int. 2020 ;2020 7405421
    Fontana JD, Ferreira RL, Zuccolotto T, de Borba Dallagassa C, Wielewski LP, Chalcoski BMS, da Silva MAN, Richardi VS, Golart J, de Melo Rodovalho C.
      Any bioassay to test new chemically synthesized larvicides or phytolarvicides against Culicidae and more harmful mosquito species, such as Aedes aegypti and Aedes albopictus, which specifically transmit dengue, yellow fever, chikungunya viral fevers as well as Zika virus, or Anopheles gambiae, a vector for malaria and philariasis, requires thousands of well-developed larvae, preferably at the fourth instar stage. The natural morphogenetic cycle of Aedes spp., in the field or in the laboratory, may extend to 19 days at room temperature (e.g., 25°C) from the first permanent contact between viable eggs and water and the last stage of larval growth or metamorphosis into flying adults. Thus, accelerated sequential molting is desirable for swifter bioassays of larvicides. We achieved this goal in Aedes aegypti with very limited strategic and low-cost additions to food, such as coconut water, milk or its casein, yeast extract, and to a lesser extent, glycerol. The naturally rich coconut water was excellent for quickly attaining the population of instar IV larvae, the most advanced one before pupation, saving about a week, for subsequent larvicidal bioassays. Diluted milk, as another food source, allowed an even faster final ecdysis and adults are useful for mosquito taxonomical purpose.
    DOI:  https://doi.org/10.1155/2020/7405421
  9. Parasit Vectors. 2020 Sep 10. 13(1): 465
    Adedeji EO, Ogunlana OO, Fatumo S, Beder T, Ajamma Y, Koenig R, Adebiyi E.
      The increasing resistance to currently available insecticides in the malaria vector, Anopheles mosquitoes, hampers their use as an effective vector control strategy for the prevention of malaria transmission. Therefore, there is need for new insecticides and/or alternative vector control strategies, the development of which relies on the identification of possible targets in Anopheles. Some known and promising targets for the prevention or control of malaria transmission exist among Anopheles metabolic proteins. This review aims to elucidate the current and potential contribution of Anopheles metabolic proteins to malaria transmission and control. Highlighted are the roles of metabolic proteins as insecticide targets, in blood digestion and immune response as well as their contribution to insecticide resistance and Plasmodium parasite development. Furthermore, strategies by which these metabolic proteins can be utilized for vector control are described. Inhibitors of Anopheles metabolic proteins that are designed based on target specificity can yield insecticides with no significant toxicity to non-target species. These metabolic modulators combined with each other or with synergists, sterilants, and transmission-blocking agents in a single product, can yield potent malaria intervention strategies. These combinations can provide multiple means of controlling the vector. Also, they can help to slow down the development of insecticide resistance. Moreover, some metabolic proteins can be modulated for mosquito population replacement or suppression strategies, which will significantly help to curb malaria transmission.
    Keywords:  Acetylcholinesterase; Immune response; Insecticide; Insecticide resistance; Plasmodium; Vector control
    DOI:  https://doi.org/10.1186/s13071-020-04342-5
  10. Sci Rep. 2020 Sep 10. 10(1): 14899
    Camargo C, Ahmed-Braimah YH, Amaro IA, Harrington LC, Wolfner MF, Avila FW.
      Aedes aegypti mosquitoes are the primary vectors of numerous viruses that impact human health. As manipulation of reproduction has been proposed to suppress mosquito populations, elucidation of biological processes that enable males and females to successfully reproduce is necessary. One essential process is female sperm storage in specialized structures called spermathecae. Aedes aegypti females typically mate once, requiring them to maintain sperm viably to fertilize eggs they lay over their lifetime. Spermathecal gene products are required for Drosophila sperm storage and sperm viability, and a spermathecal-derived heme peroxidase is required for long-term Anopheles gambiae fertility. Products of the Ae. aegypti spermathecae, and their response to mating, are largely unknown. Further, although female blood-feeding is essential for anautogenous mosquito reproduction, the transcriptional response to blood-ingestion remains undefined in any reproductive tissue. We conducted an RNAseq analysis of spermathecae from unfed virgins, mated only, and mated and blood-fed females at 6, 24, and 72 h post-mating and identified significant differentially expressed genes in each group at each timepoint. A blood-meal following mating induced a greater transcriptional response in the spermathecae than mating alone. This study provides the first view of elicited mRNA changes in the spermathecae by a blood-meal in mated females.
    DOI:  https://doi.org/10.1038/s41598-020-71904-z
  11. Proc Natl Acad Sci U S A. 2020 Sep 10. pii: 201914814. [Epub ahead of print]
    Manokaran G, Flores HA, Dickson CT, Narayana VK, Kanojia K, Dayalan S, Tull D, McConville MJ, Mackenzie JM, Simmons CP.
      Wolbachia-infected mosquitoes are refractory to flavivirus infections, but the role of lipids in Wolbachia-mediated virus blocking remains to be elucidated. Here, we use liquid chromatography mass spectrometry to provide a comprehensive picture of the lipidome of Aedes aegypti (Aag2) cells infected with Wolbachia only, either dengue or Zika virus only, and Wolbachia-infected Aag2 cells superinfected with either dengue or Zika virus. This approach identifies a class of lipids, acyl-carnitines, as being down-regulated during Wolbachia infection. Furthermore, treatment with an acyl-carnitine inhibitor assigns a crucial role for acyl-carnitines in the replication of dengue and Zika viruses. In contrast, depletion of acyl-carnitines increases Wolbachia density while addition of commercially available acyl-carnitines impairs Wolbachia production. Finally, we show an increase in flavivirus infection of Wolbachia-infected cells with the addition of acyl-carnitines. This study uncovers a previously unknown role for acyl-carnitines in this tripartite interaction that suggests an important and broad mechanism that underpins Wolbachia-mediated pathogen blocking.
    Keywords:  Wolbachia; flavivirus; lipids
    DOI:  https://doi.org/10.1073/pnas.1914814117
  12. Annu Rev Microbiol. 2020 Sep 08. 74 455-475
    Caragata EP, Dong S, Dong Y, Simões ML, Tikhe CV, Dimopoulos G.
      Mosquito-transmitted diseases, including malaria and dengue, are a major threat to human health around the globe, affecting millions each year. A diverse array of next-generation tools has been designed to eliminate mosquito populations or to replace them with mosquitoes that are less capable of transmitting key pathogens. Many of these new approaches have been built on recent advances in CRISPR/Cas9-based genome editing. These initiatives have driven the development of pathogen-resistant lines, new genetics-based sexing methods, and new methods of driving desirable genetic traits into mosquito populations. Many other emerging tools involve microorganisms, including two strategies involving Wolbachia that are achieving great success in the field. At the same time, other mosquito-associated bacteria, fungi, and even viruses represent untapped sources of new mosquitocidal or antipathogen compounds. Although there are still hurdles to be overcome, the prospect that such approaches will reduce the impact of these diseases is highly encouraging.
    Keywords:  Wolbachia; biopesticides; gene drive; mosquito-transmitted disease; sterile insect technique; transgenesis
    DOI:  https://doi.org/10.1146/annurev-micro-011320-025557
  13. Vector Borne Zoonotic Dis. 2020 Sep 07.
    Korhonen EM, Suvanto MT, Uusitalo R, Faolotto G, Smura T, Sane J, Vapalahti O, Huhtamo E.
      Sindbis virus (SINV) is a mosquito-borne avian hosted virus that is widely distributed in Europe, Africa, Asia, and Oceania. Disease in humans is documented mainly from Northern Europe and South Africa and associated with genotype I. In 2018 under extremely warm climatic conditions, a small outbreak of 71 diagnosed SINV infections was recorded in Finland. We screened 52 mosquito pools (570 mosquitoes) and 223 human sera for SINV with real-time RT-PCR and the positive samples with virus isolation. One SINV strain was isolated from a pool (n = 13) of genus Ochlerotatus mosquitoes and three strains from patient serum samples. Complete genome analysis suggested all the isolates to be divergent from one another and related to previous Finnish, Swedish, and German strains. The study provides evidence of SINV strain transfer within Europe across regions with different epidemiological characteristics. Whether these are influenced by different mosquito genera involved in the transmission remains to be studied.
    Keywords:  Finland; Ochlerotatus; Sindbis virus; alphavirus; mosquito-borne virus; virus isolation
    DOI:  https://doi.org/10.1089/vbz.2019.2562
  14. Euro Surveill. 2020 Sep;25(36):
    Lazzarini L, Barzon L, Foglia F, Manfrin V, Pacenti M, Pavan G, Rassu M, Capelli G, Montarsi F, Martini S, Zanella F, Padovan MT, Russo F, Gobbi F.
      In August 2020, during the coronavirus disease (COVID-19) pandemic, five locally acquired cases of dengue virus type 1 were detected in a family cluster in Vicenza Province, North-East Italy where Aedes albopictus mosquitoes are endemic. The primary case was an importation from West Sumatra, Indonesia. This is the first outbreak of autochthonous dengue reported in Italy. During the COVID-19 pandemic, screening of febrile travelers from endemic countries is crucial in areas where competent vectors are present.
    Keywords:  Aedes albopictus; arbovirosis; autochthonous; dengue; fever; outbreak; surveillance
    DOI:  https://doi.org/10.2807/1560-7917.ES.2020.25.36.2001606
  15. Parasit Vectors. 2020 Sep 05. 13(1): 446
    Yu S, Wang P, Qin J, Zheng H, Wang J, Liu T, Yang X, Wang Y.
      BACKGROUND: Vector control with Bacillus sphaericus (Bs) is an effective way to block the transmission of malaria. However, in practical application of Bs agents, a sublethal dose effect was often caused by insufficient dosing, and it is little known whether the Bs exposure would affect the surviving mosquitoes' vector capacity to malaria.METHODS: A sublethal dose of the Bs 2362 strain was administrated to the early fourth-instar larvae of Anopheles dirus to simulate shortage use of Bs in field circumstance. To determine vector competence, mosquitoes were dissected and the oocysts in the midguts were examined on day 9-11 post-infection with Plasmodium yoelii. Meanwhile, a SYBR quantitative PCR assay was conducted to examine the transcriptional level of the key immune molecules of mosquitoes, and RNA interference was utilized to validate the role of key immune effector molecule TEP1.
    RESULTS: The sublethal dose of Bs treatment significantly reduced susceptibility of An. dirus to P. yoelii, with the decrease of P. yoelii infection intensity and rate. Although there existed a melanization response of adult An. dirus following challenge with P. yoelii, it was not involved in the decrease of vector competence as no significant difference of melanization rates and densities between the control and Bs groups was found. Further studies showed that Bs treatment significantly increased TEP1 expression in the fourth-instar larvae (L4), pupae (Pu), 48 h post-infection (hpi) and 72 hpi (P < 0.001). Further, gene-silencing of TEP1 resulted in disappearance of the Bs impact on vector competence of An. dirus to P. yoelii. Moreover, the transcriptional level of PGRP-LC and Rel2 were significantly elevated by Bs treatment with decreased expression of the negative regulator Caspar at 48 hpi, which implied that the Imd signaling pathway was upregulated by Bs exposure.
    CONCLUSIONS: Bs exposure can reduce the vector competence of An. dirus to malaria parasites through upregulating Imd signaling pathway and enhancing the expression of TEP1. The data could not only help us to understand the impact and mechanism of Bs exposure on Anopheles' vector competence to malaria but also provide us with novel clues for wiping out malaria using vector control.
    Keywords:  Anopheles dirus; Bacillus sphaericus; Imd signaling pathway; Malaria; Plasmodium yoelii; TEP1; Vector competence
    DOI:  https://doi.org/10.1186/s13071-020-04321-w
  16. Vector Borne Zoonotic Dis. 2020 Sep 09.
    Harrington LC, Foy BD, Bangs MJ.
      Eventually there may be a broadly acceptable, even perfected, substitute for the human host requirement for direct feeding experiments by arthropods, most notably mosquitoes. However, for now, direct and indirect feeding on human volunteers is an important, if not essential, tool in vector biology research (VBR). This article builds on the foundational publication by Achee et al. (2015) covering considerations for the use of human participants in VBR pursuits. The authors introduced methods involving human participation in VBR, while detailing human-landing collections (catches) as a prime example. Benedict et al. (2018) continued this theme with an overview of human participation and considerations for research that involves release of mosquito vectors into the environment. In this study, we discuss another important aspect of human use in VBR activities: considerations addressing studies that require an arthropod to feed on a live human host. Using mosquito studies as our principal example, in this study, we discuss the tremendous importance and value of this approach to support and allow study of a wide variety of factors and interactions related to our understanding of vector-borne diseases and their control. This includes establishment of laboratory colonies for test populations, characterization of essential nutrients that contribute to mosquito fitness, characterization of blood-feeding (biting) behavior and pathogen transmission, parameterization for modeling transmission dynamics, evaluation of human host attraction and/or agents that repel, and the effectiveness of antivector or parasite therapeutic drug studies.
    Keywords:  biosafety; ethics; human host; human subjects; vector biology research; vector-borne diseases
    DOI:  https://doi.org/10.1089/vbz.2020.2620
  17. Pathogens. 2020 Sep 03. pii: E728. [Epub ahead of print]9(9):
    Calvez E, Pommelet V, Somlor S, Pompon J, Viengphouthong S, Bounmany P, Chindavong TA, Xaybounsou T, Prasayasith P, Keosenhom S, Brey PT, Telle O, Choisy M, Marcombe S, Grandadam M.
      Dengue outbreaks have regularly been recorded in Lao People's Democratic Republic (PDR) since the first detection of the disease in 1979. In 2012, an integrated arbovirus surveillance network was set up in Lao PDR and an entomological surveillance has been implemented since 2016 in Vientiane Capital. Here, we report a study combining epidemiological, phylogenetic, and entomological analyzes during the largest DENV-4 epidemic ever recorded in Lao PDR (2015-2019). Strikingly, from 2015 to 2019, we reported the DENV-4 emergence and spread at the country level after two large epidemics predominated by DENV-3 and DENV-1, respectively, in 2012-2013 and 2015. Our data revealed a significant difference in the median age of the patient infected by DENV-4 compared to the other serotypes. Phylogenetic analysis demonstrated the circulation of DENV-4 Genotype I at the country level since at least 2013. The entomological surveillance showed a predominance of Aedesaegypti compared to Aedesalbopictus and high abundance of these vectors in dry and rainy seasons between 2016 and 2019, in Vientiane Capital. Overall, these results emphasized the importance of an integrated approach to evaluate factors, which could impact the circulation and the epidemiological profile of dengue viruses, especially in endemic countries like Lao PDR.
    Keywords:  Aedes vectors; DENV-4; Lao PDR; dengue; epidemic; phylogeny
    DOI:  https://doi.org/10.3390/pathogens9090728
  18. PLoS Negl Trop Dis. 2020 Sep 08. 14(9): e0008365
    Norris EJ, Mullis AS, Phanse Y, Narasimhan B, Coats JR, Bartholomay LC.
      Insecticide resistance poses a significant threat to the control of arthropods that transmit disease agents. Nanoparticle carriers offer exciting opportunities to expand the armamentarium of insecticides available for public health and other pests. Most chemical insecticides are delivered by contact or feeding, and from there must penetrate various biological membranes to reach target organs and kill the pest organism. Nanoparticles have been shown to improve bioactive compound navigation of such barriers in vertebrates, but have not been well-explored in arthropods. In this study, we explored the potential of polyanhydride micro- and nanoparticles (250 nm- 3 μm), labeled with rhodamine B to associate with and/or transit across insect biological barriers, including the cuticle, epithelium, midgut and ovaries, in female Ae. aeygpti mosquitoes. Mosquitoes were exposed using conditions to mimic surface contact with a residual spray or paint, topical exposure to mimic contact with aerosolized insecticide, or per os in a sugar meal. In surface contact experiments, microparticles were sometimes observed in association with the exterior of the insect cuticle. Nanoparticles were more uniformly distributed across exterior tissues and present at higher concentrations. Furthermore, by surface contact, topical exposure, or per os, particles were detected in internal organs. In every experiment, amphiphilic polyanhydride nanoparticles associated with internal tissues to a higher degree than hydrophobic nanoparticles. In vitro, nanoparticles associated with Aedes aegypti Aag2 cells within two hours of exposure, and particles were evident in the cytoplasm. Further studies demonstrated that particle uptake is dependent on caveolae-mediated endocytosis. The propensity of these nanoparticles to cross biological barriers including the cuticle, to localize in target tissue sites of interest, and to reach the cytoplasm of cells, provides great promise for targeted delivery of insecticidal candidates that cannot otherwise reach these cellular and subcellular locations.
    DOI:  https://doi.org/10.1371/journal.pntd.0008365
  19. Int J Environ Res Public Health. 2020 Sep 08. pii: E6537. [Epub ahead of print]17(18):
    Santos JPC, Honório NA, Barcellos C, Nobre AA.
      INTRODUCTION: Rio de Janeiro is the second-largest city in Brazil, with strong socio-spatial segregation, and diverse and heterogeneous land use, occupation, and landscapes. The complexity of dengue requires the construction of surveillance and control tools that take into account the historical, social, economic, and environmental processes mediated in the territory as a central axis of public policy. In this context, this study aimed to stratify the city into areas of receptivity to dengue, using innovative "territorial indicators" because they are built based on the actual occupation of the territory.METHODS: We designed and constructed 17 indicators that sought to characterize the transformed and inhabited space according to receptivity to dengue. We used data on land use and occupation, connectivity, climate, and landscape. We developed the dengue receptivity through principal component analysis (PCA), using multiple criteria analysis and map algebra integrated in a GIS platform.
    RESULTS: The most receptive areas were concentrated in the transition between the north and west zones of the city, a region of unconsolidated urban sprawl. The areas of greatest receptivity had the highest incidence and density of Aedes eggs during the study period. The correlation between receptivity index and incidence rate was positive in the epidemic years.
    CONCLUSION: The proposed set of indicators was able to identify areas of greater receptivity, such as regions of disorderly urban sprawl, with a concentration of social and environmental processes that are related to the occurrence of dengue outbreaks and high vector density. On the other hand, population immunity plays an important role in the spatial distribution of dengue during non-epidemic years.
    Keywords:  Rio de Janeiro; arbovirus; dengue; receptivity; territory
    DOI:  https://doi.org/10.3390/ijerph17186537
  20. Pathogens. 2020 Sep 08. pii: E738. [Epub ahead of print]9(9):
    Diagne CT, Bengue M, Choumet V, Hamel R, Pompon J, Missé D.
      Mayaro virus (MAYV), isolated for the first time in Trinidad and Tobago, has captured the attention of public health authorities worldwide following recent outbreaks in the Americas. It has a propensity to be exported outside its original geographical range, because of the vast distribution of its vectors. Moreover, most of the world population is immunologically naïve with respect to infection with MAYV which makes this virus a true threat. The recent invasion of several countries by Aedesalbopictus underscores the risk of potential urban transmission of MAYV in both tropical and temperate regions. In humans, the clinical manifestations of MAYV disease range from mild fever, rash, and joint pain to arthralgia. In the absence of a licensed vaccine and clinically proven therapeutics against Mayaro fever, prevention focuses mainly on household mosquito control. However, as demonstrated for other arboviruses, mosquito control is rather inefficient for outbreak management and alternative approaches to contain the spread of MAYV are therefore necessary. Despite its strong epidemic potential, little is currently known about MAYV. This review addresses various aspects of MAYV, including its epidemiology, vector biology, mode of transmission, and clinical complications, as well as the latest developments in MAYV diagnosis.
    Keywords:  Aedes; Mayaro; Togaviridae; alphavirus; emerging arbovirus; vector competence
    DOI:  https://doi.org/10.3390/pathogens9090738
  21. Trop Med Infect Dis. 2020 Sep 07. pii: E142. [Epub ahead of print]5(3):
    Kading RC, Brault AC, Beckham JD.
      When this special.
    Keywords:  emerging infectious diseases; mosquito; one health; tick; vector-borne diseases
    DOI:  https://doi.org/10.3390/tropicalmed5030142