bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒10‒25
28 papers selected by
Richard Halfpenny
Staffordshire University

  1. PLoS One. 2020 ;15(10): e0240363
    Hwang MJ, Kim HC, Klein TA, Chong ST, Sim K, Chung Y, Cheong HK.
      INTRODUCTION: A number of studies have been conducted on the relationship between the distribution of mosquito abundance and meteorological variables. However, few studies have specifically provided specific ranges of temperatures for estimating the maximum abundance of mosquitoes as an empirical basis for climatic dynamics for estimating mosquito-borne infectious disease risks.METHODS: Adult mosquitoes were collected for three consecutive nights/week using Mosquito Magnet® Independence® model traps during 2018 and 2019 at US Army Garrison (USAG) Humphreys, Pyeongtaek, Gyeonggi Province, Republic of Korea (ROK). An estimate of daily mean temperatures (provided by the Korea Meteorological Administration) were distributed at the maximum abundance for selected species of mosquitoes using daily mosquito collection data after controlling for mosquito ecological cycles and environmental factors.
    RESULTS: Using the Monte-Carlo simulation, the overall mosquito population abundance peaked at 22.7°C (2.5th-97.5th: 21.7°C-23.8°C). Aedes albopictus, vector of Zika, chikungunya, dengue fever and other viruses, abundance peaked at 24.6°C (2.5th-97.5th, 22.3°C-25.6°C), while Japanese encephalitis virus (JEV) vectors, e.g., Culex tritaeniorhynchus and Culex pipiens, peaked at 24.3°C (2.5th-97.5th: 21.9°C-26.3°C) and 22.6°C (2.5th-97.5th: 21.9°C-25.2°C), respectively. Members of the Anopheles Hyrcanus Group, some of which are vivax malaria vectors in the ROK, abundance peaked at 22.4°C (2.5th-97.5th: 21.5°C-23.8°C).
    CONCLUSION: The empirical mean temperature ranges for maximum abundance were determined for each mosquito species collected at USAG Humphreys. These data contributed to the identification of relative mosquito abundance patterns for estimating mosquito-borne disease risks and developing and implementing disease prevention practices.
  2. Am J Trop Med Hyg. 2020 Oct 15.
    Rund SSC, Labb LF, Benefiel OM, Duffield GE.
      Aedes aegypti mosquito is a major vector of arboviral disease. Here, we report that the biting behavior of normally daytime active anthropophilic Ae. aegypti mosquitoes on human hosts is abnormally increased at night following exposure to artificial light at night (ALAN). Biting was examined using a human host assay where caged mosquitoes were exposed to a human arm and blood-feeding measured. Mosquitoes were tested during the daytime, nighttime, or challenged with ALAN. As predicted from the Ae. aegypti biting cycle, maximal biting occurred during daytime and lowest level occurred at night. Biting in the ALAN group was increased compared with time-matched nighttime controls. These data reveal that exposure to ALAN increases nocturnal blood-feeding behavior. This finding highlights the concern that globally increasing levels of light pollution could be impacting arboviral disease transmission, such as dengue fever and Zika, and has implications for application of countermeasures for mosquito vector control.
  3. Parasit Vectors. 2020 Oct 17. 13(1): 525
    Sumarnrote A, Overgaard HJ, Corbel V, Thanispong K, Chareonviriyaphap T, Manguin S.
      BACKGROUND: Members of the Anopheles hyrcanus group have been incriminated as important malaria vectors. This study aims to identify the species and explore the insecticide susceptibility profile within the Anopheles hyrcanus group in Ubon Ratchathani Province, northeastern Thailand where increasing numbers of malaria cases were reported in 2014.METHODS: Between 2013 and 2015, five rounds of mosquito collections were conducted using human landing and cattle bait techniques during both the rainy and dry seasons. Anopheles mosquitoes were morphologically identified and their insecticide susceptibility status was investigated. Synergist bioassays were carried out with An. hyrcanus (s.l.) due to their resistance to all insecticides. An ITS2-PCR assay was conducted to identify to species the Hyrcanus group specimens.
    RESULTS: Out of 10,361 Anopheles females collected, representing 18 taxa in 2 subgenera, 71.8% were morphologically identified as belonging to the Hyrcanus Group (subgenus Anopheles), followed by An. barbirostris group (7.9%), An. nivipes (6.5%), An. philippinensis (5.9%) and the other 14 Anopheles species. Specimens of the Hyrcanus Group were more prevalent during the rainy season and were found to be highly zoophilic. Anopheles hyrcanus (s.l.) was active throughout the night, with an early peak of activity between 18:00 h and 21:00 h. ITS2-PCR assay conducted on 603 DNA samples from specimens within the Hyrcanus Group showed the presence of five sisters species. Anopheles peditaeniatus was the most abundant species (90.5%, n = 546), followed by An. nitidus (4.5%, n = 27), An. nigerrimus (4.3%, n = 26), An. argyropus (0.5%, n = 3), and An. sinensis (0.2%, n = 1). All An. hyrcanus (s.l.) specimens that were found resistant to insecticides (deltamethrin 0.05%, permethrin 0.75% and DDT 4% and synergist tests) belonged to An. peditaeniatus. The degree of resistance in An. peditaeniatus to each of these three insecticides was approximately 50%. Addition of PBO (Piperonyl butoxide), but not DEF (S.S.S-tributyl phosphotritioate), seemed to restore susceptibility, indicating a potential role of oxidases as a detoxifying enzyme resistance mechanism.
    CONCLUSIONS: A better understanding of mosquito diversity related to host preference, biting activity and insecticide resistance status will facilitate the implementation of locally adapted vector control strategies.
    Keywords:  Anopheles hyrcanus; Insecticide resistance; Malaria vectors; Species diversity; Thailand; Ubon Ratchathani Province
  4. Trans R Soc Trop Med Hyg. 2020 Oct 22. pii: traa113. [Epub ahead of print]
    Wragge SE, Venter N, Touré D, Hunt RH, Coetzee M.
      BACKGROUND: The SEMOS gold mine in Sadiola, southwestern Mali, has been implementing a malaria vector control programme for 15 y using indoor residual house spraying and sporadic larval control. Periodic screening of the vector populations have been carried out over the years to provide information to the control programme, mainly on vector species present and their insecticide resistance status. The data from five entomological surveys, carried out in 2006, 2011, 2014, 2016 and 2018, are presented.METHODS: Adult mosquitoes were collected resting on walls inside houses and on verandas. Insecticide susceptibility assays were carried out and mosquitoes subsequently identified by species using molecular assays.
    RESULTS: The major malaria vector mosquitoes, Anopheles gambiae and Anopheles arabiensis were abundant at each sampling period with Anopheles coluzzii and Anopheles funestus being rare or absent. Anopheles rivulorum was identified in 2006 and Anopheles leesoni in 2016. The presence of Anopheles rivulorum-like, identified for the first time in 2018, was not screened for in previous surveys. Insecticide susceptibility bioassays showed resistance in both A. gambiae and A. arabiensis to pyrethroids, carbamates and dichlorodiphenyltrichloroethane over the 12 y.
    CONCLUSIONS: This is the first record of A. rivulorum-like west of Côte d'Ivoire. Resistance levels to the three classes of insecticides were variable but appeared to decrease after pyrethroids were discontinued for house spraying.
    Keywords:   Anopheles funestus, Anopheles gambiae complex; Anopheles rivulorum-like; Mali; Sadiola; insecticide resistance
  5. J Med Entomol. 2020 Oct 24. pii: tjaa217. [Epub ahead of print]
    Delgado-Serra S, Viader M, Ruiz-Arrondo I, Miranda MÁ, Barceló C, Bueno-Marí R, Hernández-Triana LM, Miquel M, Lester K, Jurado-Rivera JA, Paredes-Esquivel C.
      Several outbreaks of mosquito-borne diseases have taken place in Europe in recent years. In Spain, both active and passive surveillance have demonstrated that dengue and West Nile viruses are currently circulating, and seven autochthonous dengue cases have been reported in the last 2 yr. The effectiveness of vector control programs largely depends on the accuracy of the taxonomic identification of the species. However, in Spain, identification almost completely relies on the use of morphological keys to characterize the mosquito fauna. This study investigates the congruence between molecular and morphological species boundaries in 13 Spanish mosquito taxa. The Cytochrome c oxidase subunit I (COI) gene region was sequenced from 60 adult specimens collected in Mallorca, plus several representatives from other Spanish regions for comparative purposes. Phylogenetic relationships were established using Bayesian and maximum-likelihood approaches. Using three species delimitation algorithms (ABGD, mPTP, and GMYC), we found strong evidence for cryptic speciation within Anopheles algeriensis Theobald, a widespread mosquito in the Mediterranean basin. We also delimited the Mallorcan rock pool mosquito Aedes mariae (Sergent & Sergent), from mainland European populations. Finally, we found difficulties in the use of wing characters in species keys to distinguish Culiseta annulata (Schrk) from Culiseta subochrea (Edwards). Given that these species are vectors of pathogens of medical relevance and have veterinary importance, their accurate taxonomic identification is essential in European vector surveillance programs.
  6. Vector Borne Zoonotic Dis. 2020 Oct 21.
    Rexhepi A, Sherifi K, Berxholi K, Xhekaj B, Muja-Bajraktari N, Özkul A, von Possel R, Emmerich P.
      This study was conducted to assess the presence of West Nile virus (WNV) in Kosovo by serological testing of apparently healthy local horses and free-range chicken, and it attempted to detect viral nucleic acid in birds and mosquitoes. Between January 2018 and June 2019, 260 equine serum samples were collected, additionally 580 adult mosquitoes (53 pools) were grouped in for genera, including Culex spp. (226 individuals; 26 pools), Aedes spp. (136 individuals; 16 pools), Anopheles spp. (184 individuals; 7 pools), and Culiseta spp. (34 individuals; 4 pools). Fifty domestic birds and 51 wild birds were collected from different regions of Kosovo. Equine and domestic bird serum samples were tested by flavivirus IgG enzyme-linked immunosorbent assay (ELISA), while mosquitoes and bird viscera were tested for WNV RNA by RT-qPCR. All ELISA-positive results were confirmed by plaque reduction neutralization test (PRNT) and eight by virus neutralization test. WNV antibodies were present in 27 out of 260 equine sera (10.38%) and one out of 50 samples in domestic birds by ELISA and PRNT. Eight of 27 positive equine serum samples with high titer neutralized WNV, but not Usutu virus. No WNV RNA was detected in birds or mosquitoes. The occurrence of WNV antibodies in local equines from all regions of Kosovo indicates that the virus is circulating within the country. Public health authorities should therefore plan a risk assessment and disease control program.
    Keywords:  Kosovo; West Nile virus; birds; equines; mosquitoes
  7. Trop Med Infect Dis. 2020 Oct 20. pii: E161. [Epub ahead of print]5(4):
    Rocha EM, Katak RM, Campos de Oliveira J, Araujo MDS, Carlos BC, Galizi R, Tripet F, Marinotti O, Souza-Neto JA.
      In Brazil, malaria transmission is mostly confined to the Amazon, where substantial progress has been made towards disease control in the past decade. Vector control has been historically considered a fundamental part of the main malaria control programs implemented in Brazil. However, the conventional vector-control tools have been insufficient to control or eliminate local vector populations due to the complexity of the Amazonian rainforest environment and ecological features of malaria vector species in the Amazon, especially Anopheles darlingi. Malaria elimination in Brazil and worldwide eradication will require a combination of conventional and new approaches that takes into account the regional specificities of vector populations and malaria transmission dynamics. Here we present an overview on both conventional and novel promising vector-focused tools to curb malaria transmission in the Brazilian Amazon. If well designed and employed, vector-based approaches may improve the implementation of malaria-control programs, particularly in remote or difficult-to-access areas and in regions where existing interventions have been unable to eliminate disease transmission. However, much effort still has to be put into research expanding the knowledge of neotropical malaria vectors to set the steppingstones for the optimization of conventional and development of innovative vector-control tools.
    Keywords:  Amazon; Anopheles darlingi; Brazil; Plasmodium; challenges; control; conventional; malaria; mosquito; novel; strategies; vector
  8. Pathogens. 2020 Oct 21. pii: E859. [Epub ahead of print]9(10):
    Morales-Vargas RE, Missé D, Chavez IF, Kittayapong P.
      Dynamics of dengue serotype 2 virus isolated from patients with different disease severity, namely flu-like classic dengue fever (DF) and dengue shock syndrome (DSS) were studied in its mosquito vector Aedes aegypti. We compared isolate infectivity and vector competence (VC) among thirty two A. aegypti-viral isolate pairs. Mosquito populations from high dengue incidence area exhibited overall greater VC than those from low dengue incidence area at 58.1% and 52.5%, respectively. On the other hand, the overall infection rates for the isolates ThNR2/772 (DF, 62.3%) and ThNR2/391 (DSS, 60.9%), were significantly higher than those for isolates ThNR2/406 (DF, 55.2%) and ThNR2/479 (DSS, 54.8%). These results suggest that the efficacy of dengue virus circulation was likely to vary according to the combination between the virus strains and origin of the mosquito strains, and this may have epidemiologic implications toward the incidence of flu-like classic dengue fever (DF) and dengue shock syndrome (DSS).
    Keywords:  dengue virus; disease severity; vector competence
  9. PLoS Negl Trop Dis. 2020 Oct 23. 14(10): e0008805
    Knerer G, Currie CSM, Brailsford SC.
      BACKGROUND AND AIMS: Dengue fever is a major public health problem in tropical/subtropical regions. Prior economic analyses have predominantly evaluated either vaccination or vector-control programmes in isolation and do not really consider the incremental benefits and cost-effectiveness of mixed strategies and combination control. We estimated the cost-effectiveness of single and combined approaches in Thailand.METHODS: The impacts of different control interventions were analysed using a previously published mathematical model of dengue epidemiology and control incorporating seasonality, age structure, consecutive infection, cross protection, immune enhancement and combined vector-host transmission. An economic model was applied to simulation results to estimate the cost-effectiveness of 4 interventions and their various combinations (6 strategies): i) routine vaccination of 1-year olds; ii) chemical vector control strategies targeting adult and larval stages separately; iii) environmental management/ public health education and awareness [EM/ PHEA]). Payer and societal perspectives were considered. The health burden of dengue fever was assessed using disability-adjusted life-years (DALYs) lost. Costs and effects were assessed for 10 years. Costs were discounted at 3% annually and updated to 2013 United States Dollars. Incremental cost-effectiveness analysis was carried out after strategies were rank-ordered by cost, with results presented in a table of incremental analysis. Sensitivity and scenario analyses were undertaken; and the impact and cost-effectiveness of Wolbachia was evaluated in exploratory scenario analyses.
    RESULTS: From the payer and societal perspectives, 2 combination strategies were considered optimal, as all other control strategies were dominated. Vaccination plus adulticide plus EM/ PHEA was deemed cost-effective according to multiple cost-effectiveness criteria. From the societal perspective, incremental differences vs. adulticide and EM/ PHEA resulted in costs of $157.6 million and DALYs lost of 12,599, giving an expected ICER of $12,508 per DALY averted. Exploratory scenario analyses showed Wolbachia to be highly cost-effective ($343 per DALY averted) vs. other single control measures.
    CONCLUSIONS: Our model shows that individual interventions can be cost-effective, but that important epidemiological reductions and economic impacts are demonstrated when interventions are combined as part of an integrated approach to combating dengue fever. Exploratory scenario analyses demonstrated the potential epidemiological and cost-effective impact of Wolbachia when deployed at scale on a nationwide basis. Our findings were robust in the face of sensitivity analyses.
  10. Acta Trop. 2020 Oct 20. pii: S0001-706X(20)31643-0. [Epub ahead of print] 105730
    Adeniran AA, Hernández-Triana LM, Ortega-Morales AI, Garza-Hernández JA, Cruz-Ramos J, Chan-Chable RJ, Vázquez-Marroquín R, Huerta-Jiménez H, Nikolova NI, Fooks AR, Pérez-Rodríguez MA.
      Mosquitoes are commonly identified to species level using morphological traits, but complementary methods for identification are often necessary when specimens are collected as immature stages, stored inadequately or when delineation of species complexes is problematic. DNA-barcoding using the mitochondrial cytochrome c oxidase subunit 1 (COI) gene is one such tool used for the morphological identification of species. A comprehensive entomological survey of mosquito species in Mexico State identified by COI DNA barcoding and morphology is documented in this paper. Specimens were collected from all the physiographic provinces in Mexico State between 2017 and 2019. Overall, 2,218 specimens were collected from 157 localities representing both subfamilies Anophelinae and Culicinae. A species checklist that consists of 6 tribes, 10 genera, 20 subgenera, and 51 species, 35 of which are new records for Mexico State, is provided. Three hundred and forty-two COI sequences of 46 species were analysed. Mean intraspecific and interspecific distances ranged between 0% to 3.9% and from 1.2% to 25.3%, respectively. All species groups were supported by high bootstraps values in a Neighbour-Joining analysis and new COI sequences were generated for eight species: Aedes chionotum Zavortink, Ae. vargasi Schick, Ae. gabriel Schick, Ae. guerrero Berlin, Ae. ramirezi Vargas and Downs, Haemagogus mesodentatus Komp and Kumm, Culex restrictor Dyar and Knab, and Uranotaenia geometrica Theobald. This study provides a detailed inventory of the Culicidae from Mexico State and discusses the utility of DNA barcoding as a complementary tool for accurate mosquito species identification in Mexico.
    Keywords:  Culicidae; DNA-Barcoding; Mexico State; Mosquitoes; Species
  11. Sci Rep. 2020 Oct 22. 10(1): 18018
    Multini LC, de Souza ALDS, Marrelli MT, Wilke ABB.
      Fragmentation of natural environments as a result of human interference has been associated with a decrease in species richness and increase in abundance of a few species that have adapted to these environments. The Brazilian Atlantic Forest, which has been undergoing an intense process of fragmentation and deforestation caused by human-made changes to the environment, is an important hotspot for malaria transmission. The main vector of simian and human malaria in this biome is the mosquito Anopheles cruzii. Anthropogenic processes reduce the availability of natural resources at the tree canopies, An. cruzii primary habitat. As a consequence, An. cruzii moves to the border of the Atlantic Forest nearing urban areas seeking resources, increasing their contact with humans in the process. We hypothesized that different levels of anthropogenic changes to the environment can be an important factor in driving the genetic structure and diversity in An. cruzii populations. Five different hypotheses using a cross-sectional and a longitudinal design were tested to assess genetic structure in sympatric An. cruzii populations and microevolutionary processes driving these populations. Single nucleotide polymorphisms were used to assess microgeographic genetic structure in An. cruzii populations in a low-endemicity area in the city of São Paulo, Brazil. Our results show an overall weak genetic structure among the populations, indicating a high gene flow system. However, our results also pointed to the presence of significant genetic structure between sympatric An. cruzii populations collected at ground and tree-canopy habitats in the urban environment and higher genetic variation in the ground-level population. This indicates that anthropogenic modifications leading to habitat fragmentation and a higher genetic diversity and structure in ground-level populations could be driving the behavior of An. cruzii, ultimately increasing its contact with humans. Understanding how anthropogenic changes in natural areas affect An. cruzii is essential for the development of more effective mosquito control strategies and, on a broader scale, for malaria-elimination efforts in the Brazilian Atlantic Forest.
  12. Biomed Res Int. 2020 ;2020 8732473
    Gunathilaka N, Ranasinghe K, Amarasinghe D, Rodrigo W, Mallawarachchi H, Chandrasena N.
      Background: Larval and adult mosquito stages harbor different extracellular microbes exhibiting various functions in their digestive tract including host-parasite interactions. Midgut symbiotic bacteria can be genetically exploited to express molecules within the vectors, altering vector competency and potential for disease transmission. Therefore, identification of mosquito gut inhabiting microbiota is of ample importance before developing novel vector control strategies that involve modification of vectors.Method: Adult mosquitoes of Culex tritaeniorhynchus, Culex gelidus, and Mansonia annulifera were collected from selected Medical Officer of Health (MOH) areas in the Gampaha district of Sri Lanka. Midgut lysates of the field-caught non-blood-fed female mosquitoes were cultured in Plate Count Agar medium, and Prokaryotic 16S ribosomal RNA partial genes of the isolated bacteria colonies were amplified followed by DNA sequencing. Diversity indices were used to assess the diversity and richness of the bacterial isolates in three mosquito species. The distribution pattern of bacterial isolates between different mosquito species was assessed by Distance-Based Redundancy Analysis (dbRDA).
    Results: A total of 20 bacterial species (Staphylococcus pasteuri, Bacillus megaterium, Staphylococcus cohnii, Pantoea dispersa, Staphylococcus chromogenes, Bacillus aquimaris, Staphylococcus arlettae, Staphylococcus sciuri, Staphylococcus warneri, Moraxella osloensis, Enterobacter sp., Klebsiella michiganensis, Staphylococcus hominis, Staphylococcus saprophyticus, Streptomyces sp., Bacillus niacin, Cedecea neteri, Micrococcus luteus, Lysinibacillus sphaericus, and Bacillus licheniformis) were identified. All of these species belonged to three phyla, Proteobacteria, Firmicutes, and Actinobacteria, out of which phylum Firmicutes (71.1%) was the most prominent. The least number of species was recorded from Actinobacteria. The relative distribution of midgut microbes in different mosquito species differed significantly among mosquito species (Chi-square, χ 2 = 486.091; df = 36; P ≤ 0.001). Midgut microbiota of Cx. tritaeniorhynchus and Cx. gelidus indicated a similarity of 21.51%, while Ma. annulifera shared a similarity of 6.92% with the cluster of above two species. The gut microbiota of Cx. tritaeniorhynchus was also significantly more diverse and more evenly distributed compared to Ma. annulifera. Simpson's diversity, Margalef's diversity, and Menhinick's diversity indices were higher in Cx. gelidus. Of the recorded species, P. dispersa and strains of nonpathogenic species in Bacillaceae family (B. megaterium, B. niacini, B. licheniformis, and L. sphaericus) can be recommended as potential candidates for paratransgenesis.
    Conclusion: The relative distribution of midgut microbes in different mosquito species differed significantly among the three studied adult mosquito species. The present data strongly encourage further investigations to explore the potential usage of these microbes through paratransgenic approach for novel eco-friendly vector control strategies.
  13. F1000Res. 2020 ;9 1032
    Bokore GE, Ouma P, Onyango PO, Bukhari T, Fillinger U.
      Background: Strategies that involve manipulations of the odour-orientation of gravid malaria vectors could lead to novel attract-and-kill interventions. Recent work has highlighted the potential involvement of graminoid plants in luring vectors to oviposition sites. This study aimed to analyse the association between water-indicating graminoid plants (Cyperaceae, sedges), other abiotic and biotic factors and the presence and abundance of early instar Anopheles larvae in aquatic habitats as a proxy indicator for oviposition. Methods: A cross-sectional survey of 110 aquatic habitats along the shores of Lake Victoria was done during the rainy season. Habitats were sampled for mosquito larvae using the sweep-net method and habitat characteristics recorded. Results: Anopheles arabiensis was the dominant species identified from aquatic habitats. Larvae of the secondary malaria vectors such as Anopheles coustani, An. rufipes and An. maculipalpis were found only in habitats covered with graminoids, whereas An. arabiensis, An. ziemanni and An. pharoensis were found in both habitats with and without graminoid plants. The hypothesis that sedges might be positively associated with the presence and abundance of early instar Anopheles larvae could not be confirmed. The dominant graminoid plants in the habitats were Panicum repens, Cynodon dactylon in the Poaceae family and Cyperus rotundus in the Cyperaceae family. All of these habitats supported abundant immature vector populations. The presence of early instar larvae was significantly and positively associated with swamp habitat types (OR=22, 95% CI=6-86, P<0.001) and abundance of late Anopheles larvae (OR=359, CI=33-3941, P<0.001), whilst the association was negative with tadpole presence (OR=0.1, CI=0.0.01-0.5, P=0.008). Conclusions: Early instar malaria vectors were abundant in habitats densely vegetated with graminoid plants in the study area but specific preference for any of the graminoids could not be detected. In search for oviposition cues, it might be useful to screen for chemical volatiles released from all dominant plant species.
    Keywords:  Anopheles; graminoid plants; larval ecology; malaria; oviposition; vector control; vegetation
  14. J Med Entomol. 2020 Oct 20. pii: tjaa213. [Epub ahead of print]
    Sukkanon C, Tisgratog R, Muenworn V, Bangs MJ, Hii J, Chareonviriyaphap T.
      Exophilic vectors are an important contributor to residual malaria transmission. Wearable spatial repellents (SR) can potentially provide personal protection in early evening hours before people retire indoors. An SR prototype for passive delivery of transfluthrin (TFT) for protecting humans against nocturnal mosquitoes in Kanchanaburi, western Thailand, is evaluated. A plastic polyethylene terephthalate (PET) sheet (676 cm2) treated with 55-mg TFT (TFT-PET), attached to the back of short-sleeve vest worn by human collector, was evaluated under semifield and outdoor conditions. Field-caught, nonblood-fed female Anopheles minimus s.l. were released in a 40 m length, semifield screened enclosure. Two collectors positioned at opposite ends conducted 12-h human-landing collections (HLC). The outdoor experiment was conducted between treatments among four collectors at four equidistant positions who performed HLC. Both trials were conducted for 30 consecutive nights. TFT-PET provided 67% greater protection (P < 0.001) for 12 h compared with unprotected control, a threefold reduction in the attack. In outdoor trials, TFT-PET provided only 16% protection against An. harrisoni Harbach & Manguin (Diptera: Culicidae) compared with unprotected collector (P = 0.0213). The TFT-PET vest reduced nonanophelines landing by 1.4-fold compared with the PET control with a 29% protective efficacy. These findings suggest that TFT-PET had diminished protective efficacy in an open field environment. Nonetheless, the concept of a wearable TFT emanatory device has the potential for protecting against outdoor biting mosquitoes. Further development of portable SR tools is required, active ingredient selection and dose optimization, and more suitable device design and materials for advancing product feasibility.
    Keywords:   Anopheles harrisoni ; Anopheles minimus s.l; outdoor transmission; spatial repellency; transfluthrin
  15. BMC Vet Res. 2020 Oct 23. 16(1): 402
    Tahir D, Meyer LN, Lekouch N, Varloud M.
      BACKGROUND: Mosquitoes are vectors of several pathogens of considerable importance to humans and companion animals, including nematode helminths such as Dirofilaria immitis and Dirofilaria repens that cause heartworm disease and subcutaneous dirofilariosis, respectively. In addition to mosquito-borne pathogen transmission, mosquito bites can cause discomfort and irritation in pets, and even lead to severe hypersensitivity reactions. In the present study, we report an acute local hypersensitivity reaction in a dog following experimental exposure to Aedes (Stegomyia) aegypti.CASE PRESENTATION: A healthy six-year-old male beagle was included in an efficacy study in which dogs (n = 28) were exposed to Ae. aegypti mosquitoes. On Day - 6, the dog was allocated to one of the study groups, consisting of seven dogs to be treated on Day 0 with an imidacloprid/flumethrin collar. After sedation, animals were exposed to approximately 50 females of Ae. aegypti for 60 (± 5) minutes on Days - 6, 1, 7, 14, 21, 28, 55, and 83. On Day - 6, no allergic reaction to the mosquito bites was observed. However, on Day 1, corresponding to the second challenge, the dog demonstrated an acute allergic reaction characterized by swelling of the face (especially in the base of the muzzle and around the eyes), redness of the eyes, and conjunctival edema of the right eye was also observed. The dog was immediately treated with an intramuscular injection of a commercially available antihistamine treatment, Pen-Hista-Strep® containing a suspension of benzylpenicillin, chlorphenamine, dexamethasone, dihydrostreptomycin, and procaine at a dosage of 1 mL per 10 kg. A few hours after treatment, the dog showed noticeable improvement.
    CONCLUSIONS: This case provides the first evidence of canine acute local hypersensitivity reaction to mosquito bites under laboratory conditions. This observation suggests that invasive mosquito species such as Aedes spp. may affect the health and comfort of our companion animals, especially for pets with outdoor access without individual protective measures against insect bites.
    Keywords:  Aedes aegypti; Case report; Dog; Hypersensitivity; Protective measures
  16. iScience. 2020 Oct 23. 23(10): 101572
    Huang B, Yang Q, Hoffmann AA, Ritchie SA, van den Hurk AF, Warrilow D.
      A dengue suppression strategy based on release of Aedes aegypti mosquitoes infected with the bacterium Wolbachia pipientis is being trialed in many countries. Wolbachia inhibits replication and transmission of dengue viruses. Questions remain regarding the long-term stability of virus-suppressive effects. We sequenced the Wolbachia genome and analyzed Ae. aegypti mitochondrial DNA markers isolated from mosquitoes sampled 2-8 years after releases in the greater Cairns region, Australia. Few changes were detected when Wolbachia genomes of field mosquitoes were compared with Wolbachia genomes of mosquitoes obtained soon after initial releases. Mitochondrial variants associated with the initial Wolbachia release stock are now the only variants found in release sites, highlighting maternal leakage as a possible explanation for rare Wolbachia-negative mosquitoes and not migration from non-release areas. There is no evidence of changes in the Wolbachia genome that indicate selection against its viral-suppressive effects or other phenotypes attributable to infection with the bacterium.
    Keywords:  Biological Sciences; Entomology; Genomics; Parasitology; Virology
  17. Proc Natl Acad Sci U S A. 2020 Oct 21. pii: 202015095. [Epub ahead of print]
    Vial T, Tan WL, Deharo E, Missé D, Marti G, Pompon J.
      Dengue virus (DENV) subdues cell membranes for its cellular cycle by reconfiguring phospholipids in humans and mosquitoes. Here, we determined how and why DENV reconfigures phospholipids in the mosquito vector. By inhibiting and activating the de novo phospholipid biosynthesis, we demonstrated the antiviral impact of de novo-produced phospholipids. In line with the virus hijacking lipids for its benefit, metabolomics analyses indicated that DENV actively inhibited the de novo phospholipid pathway and instead triggered phospholipid remodeling. We demonstrated the early induction of remodeling during infection by using isotope tracing in mosquito cells. We then confirmed in mosquitoes the antiviral impact of de novo phospholipids by supplementing infectious blood meals with a de novo phospholipid precursor. Eventually, we determined that phospholipid reconfiguration was required for viral genome replication but not for the other steps of the virus cellular cycle. Overall, we now propose that DENV reconfigures phospholipids through the remodeling cycle to modify the endomembrane and facilitate formation of the replication complex. Furthermore, our study identified de novo phospholipid precursor as a blood determinant of DENV human-to-mosquito transmission.
    Keywords:  dengue; metabolomics; mosquito; phospholipid; replication
  18. J Med Entomol. 2020 Oct 19. pii: tjaa215. [Epub ahead of print]
    Westby KM, Juliano SA, Medley KA.
      Aedes albopictus (Skuse) (Diptera: Culicidae) is one of the most invasive species globally, and has led to rapid declines and local extirpations of resident mosquitoes where it becomes established. A potential mechanism behind these displacements is the superior competitive ability of Ae. albopictus in larval habitats. Research on the context-dependent nature of competitive displacement predicts that Ae. albopictus will not replace native Aedes triseriatus (Say) (Diptera: Culicidae) in treeholes but could do so in artificial container habitats. Aedes albopictus remains rare in temperate treeholes but less is known about how Ae. albopictus fares in artificial containers in forests. Tyson Research Center (TRC) is a field station composed of mostly oak-hickory forest located outside Saint Louis, MO. The container community has been studied regularly at TRC since 2007 with permanently established artificial containers on the property since 2013. Aedes albopictus was detected each year when these communities were sampled; however, its abundance remains low and it fails to numerically dominate other species in these communities. We present data that show Ae. albopictus numbers have not increased in the last decade. We compare egg counts from 2007 to 2016 and combine larval sample data from 2012 to 2017.We present average larval densities and prevalence of Ae. albopictus and two competitors, Ae. triseriatus and Aedes japonicus (Theobald) (Diptera: Culicidae), as well as monthly averages by year. These data highlight a circumstance in which Ae. albopictus fails to dominate the Aedes community despite it doing so in more human-impacted habitats. We present hypotheses for these patterns based upon abiotic and biotic environmental conditions.
    Keywords:   Aedes albopictus ; Aedes japonicus ; Aedes triseriatus ; context-dependence; invasive species
  19. PLoS Negl Trop Dis. 2020 Oct 23. 14(10): e0008763
    Premkumar A, Shriram AN, Krishnamoorthy K, Subramanian S, Vasuki V, Vijayachari P, Jambulingam P.
      A group of four human inhabited Nancowry Islands in Nicobar district in the Andaman and Nicobar Islands, India having a population of 7674 is the lone focus of diurnally sub-periodic Wuchereria bancrofti (DspWB) that is transmitted by Aedes niveus (Ludlow). Microfilaria (Mf) prevalence was above 1% even after nine rounds of Mass Drug Administration (MDA) with DEC and albendazole. Molecular xenomonitoring (MX) was conducted to identify appropriate vector sampling method and assess the impact. BioGents Sentinel traps, gravid traps and human baited double bed nettraps were used in three locations in each village to collect Aedes niveus female mosquitoes. Subsequently daytime man landing collections (MLC) were carried out in all the 25 villages in the islands. Collections were compared in terms of the number of vector mosquitoes captured per trap collection. Females of Ae. niveus were pooled, dried and processed for detecting filarial parasite DNA using RT-PCR assay. Vector infection rate was estimated using PoolScreen software. Only 393 female mosquitoes including 44 Ae. niveus (11.2%) were collected from 459 trap collections using three trapping devices. From 151 MLCs, 2170 Ae. niveus female mosquitoes were collected. The average prevalence of W. bancrofti DNA was 0.43%. Estimated upper 95% CI exceeded the provisional prevalence threshold of 0.1% in all the villages, indicating continued transmission as observed in Mf survey. MLCs could be the choice, for now, to sample Ae. niveus mosquitoes. The PCR assay used in MX for nocturnally periodic bancroftian filariasis could be adopted for DspWB. The vector-parasite MX, can be used to evaluate interventions in this area after further standardization of the protocol.
  20. PLoS One. 2020 ;15(10): e0241033
    Mugenyi L, Nankabirwa JI, Arinaitwe E, Rek J, Hens N, Kamya M, Dorsey G.
      BACKGROUND: Indoor residual spraying (IRS) reduces vector densities and malaria transmission, however, the most effective spraying intervals for IRS have not been well established. We estimated the optimal timing interval for IRS using a statistical approach.METHODS: Six rounds of IRS were implemented in Tororo District, a historically high malaria transmission setting in Uganda, during the study period (3 rounds with bendiocarb active ingredient (Ficam®): December 2014 to December 2015, and 3 rounds with pirimiphos methyl active ingredient (Actellic 300®CS): June 2016 to July 2018). A generalized additive model was used to estimate the optimal timing interval for IRS based on the predicted malaria incidence. The model was fitted to clinical incidence data from a cohort of children aged 0.5-10 years from selected households observed throughout the study period.
    RESULTS: 494 children, 67% aged less than 5 years at enrolment were analysed. Six-months period incidence of malaria decreased from 2.96 per person-years at the baseline to 1.74 following the first round of IRS and then to 0.02 after 6 rounds of IRS. The optimal time interval for IRS differed between bendiocarb and pirimiphos methyl and by IRS round. To retain an optimum impact, bendiocarb would require respraying 17 (95% CI: 14.2-21.0) weeks after application whereas pirimiphos methyl could remain impactful for 40 (95% CI: 37.0-42.8) weeks, although in the final year this estimates 36 (95% CI: 32.7-37.7) weeks. However, we could not estimate from the data the optimal time after the second and third rounds of bendiocarb and after the second round of pirimiphos methyl. Neither the amount of rainfall nor the EIR nor the distribution of nets were found to be statistically significant for determining the time period between spray rounds.
    CONCLUSION: In our setting, the effect of the two IRS products was distinct. Statistically, pirimiphos methyl provided a longer window of protection than bendiocarb, although impact varied between different spray rounds and years which was not explained by rainfall or EIR or distribution of nets in our statistical approach. Understanding the effectiveness of IRS and how long it lasts can help for planning campaigns, but one should consider the financial cost and insecticide resistance. Monitoring the timing of spray campaigns using clinical incidence could be repeated in future programs to help determine the average period of protectivity of these products.
  21. PLoS Negl Trop Dis. 2020 Oct;14(10): e0008706
    Barletta ABF, Alves E Silva TL, Talyuli OAC, Luna-Gomes T, Sim S, Angleró-Rodríguez Y, Dimopoulos G, Bandeira-Melo C, Sorgine MHF.
      Prostaglandins (PGs) are immuno-active lipids that mediate the immune response in invertebrates and vertebrates. In insects, PGs play a role on different physiological processes such as reproduction, ion transport and regulation of cellular immunity. However, it is unclear whether PGs play a role in invertebrate's humoral immunity, and, if so, which immune signaling pathways would be modulated by PGs. Here, we show that Aedes aegypti gut microbiota and Gram-negative bacteria challenge induces prostaglandin production sensitive to an irreversible inhibitor of the vertebrate cyclooxygenase, acetylsalicylic acid (ASA). ASA treatment reduced PG synthesis and is associated with decreased expression of components of the Toll and IMD immune pathways, thereby rendering mosquitoes more susceptible to both bacterial and viral infections. We also shown that a cytosolic phospholipase (PLAc), one of the upstream regulators of PG synthesis, is induced by the microbiota in the midgut after blood feeding. The knockdown of the PLAc decreased prostaglandin production and enhanced the replication of Dengue in the midgut. We conclude that in Ae. aegypti, PGs control the amplitude of the immune response to guarantee an efficient pathogen clearance.
  22. Virology. 2020 Oct 06. pii: S0042-6822(20)30179-3. [Epub ahead of print]552 73-82
    Wan S, Cao S, Wang X, Zhou Y, Yan W, Gu X, Wu TC, Pang X.
      Zika virus (ZIKV) is a mosquito-borne flavivirus that replicates in both vertebrate and insect cells, whereas insect-specific flaviviruses (ISF) replicate only in insect cells. We sought to convert ZIKV, from a dual-tropic flavivirus, into an insect-specific virus for the eventual development of a safe ZIKV vaccine. Reverse genetics was used to introduce specific mutations into the furin cleavage motif within the ZIKV pre-membrane protein (prM). Mutant clones were selected, which replicated well in C6/36 insect cells but exhibited reduced replication in non-human primate (Vero) cells. Further characterization of the furin cleavage site mutants indicated they replicated poorly in both human (HeLa, U251), and baby hamster kidney (BHK-21) cells. One clone with the induced mutation in the prM protein and at positions 291and 452 within the NS3 protein was totally and stably replication-defective in vertebrate cells (VSRD-ZIKV). Preliminary studies in ZIKV sensitive, immunodeficient mice demonstrated that VSRD-ZIKV-infected mice survived and were virus-negative. Our study indicates that a reverse genetic approach targeting the furin cleavage site in prM can be used to select an insect-specific ZIKV with the potential utility as a vaccine strain.
    Keywords:  Furin; Vaccine; Vertebrate-specific replication-defective; Viral tropism; Zika virus; prM cleavage
  23. Antibodies (Basel). 2020 Oct 21. pii: E56. [Epub ahead of print]9(4):
    Marbán-Castro E, Arrieta GJ, Martínez MJ, González R, Bardají A, Menéndez C, Mattar S.
      Mosquito-borne viruses such as dengue (DENV), chikungunya (CHIKV), and Zika (ZIKV) have spread in recent decades. We aimed to assess seroprevalence of arboviral infections in pregnant women living in Cereté, Caribbean Colombia. In 2016 a cross-sectional facility-based sero-survey study was performed among pregnant women (N = 90). Most of them (66%) reported at least one symptom or sign compatible with arboviral infection over the previous 15 days. All screened women had a positive IgG for DENV, 89% for ZIKV, and 82% for CHIKV. One woman tested positive for ZIKV IgM. This study shows the high exposure among pregnant women to arboviruses in endemic areas, shown by the high seroprevalence of past arboviral infections. Given the evidence on the potential risks of these arboviral infections on pregnancy and infant outcomes, these results highlight the need for continuous epidemiological surveillance of arboviral diseases, particularly among those most of risk of their harmful consequences.
    Keywords:  Colombia; chikungunya; dengue; seroprevalence; zika
  24. Int J Infect Dis. 2020 Oct 16. pii: S1201-9712(20)32226-8. [Epub ahead of print]
    Castellanos JE, Jaimes N, Coronel-Ruiza C, Rojas JP, Mejía LF, Villarreal VH, Maya LE, Claros LM, Orjuela C, Calvo E, Muñoz MV, Velandia-Romero ML.
      OBJECTIVE: To identify the arbovirus involved in febrile cases identified in a pediatric clinic in Cali, Valle del Cauca province, Colombia, and study the clinical characteristics.METHODS: A descriptive, prospective study enrolled 345 febrile children for 12 months in a pediatric clinic. Medical record registers documenting signs and symptoms, and serum samples were analyzed to detect DENV, CHIKV, and ZIKV by reverse transcription-polymerase chain reaction and serology methods. Diagnosis at the time of admission and discharge were compared based on laboratory test results.
    RESULTS: All patients were diagnosed as severe dengue at admission. Molecular detection and serology tests identified 143 CHIKV-positive (41.4%), 20 DENV-positive (5.8%), and 123 DENV-CHIKV coinfection patients (35.7%). DENV or CHIKV serology test results of these double-infected patients yield poor performance to confirm patient cases. ZIKV infection was detected in 5 patients (1.4%), every time as double or triple infections.
    CONCLUSION: . A sustained CHIKV circulation and transmission was confirmed causing febrile illness in children and indicating that this virus spreads even during the regular DENV season, leading to double infections and altering clinical symptoms. Specific clinical tests are necessary to closely identify the arbovirus involved in causing infectious diseases that can help in better treatment and mosquito-transmitted virus surveillance.
    Keywords:  RT-PCR; arbovirus; chikungunya fever; dengue fever; serology
  25. Acta Clin Belg. 2020 Oct 22. 1-9
    Wellekens K, Betrains A, De Munter P, Peetermans W.
      BACKGROUND: Dengue is a possibly life-threatening human mosquito-borne viral infection widely spread in peridomestic (sub)tropical climates. The global incidence has expanded rapidly in the last decades, with 40% of the world's population currently at risk. To date, no anti-viral treatment other than supportive care exists. In 2015, the first and only dengue-vaccine, CYD-TDV, received marketing authorization.OBJECTIVES: To present the current understanding of dengue in terms of epidemiology, transmission, pathogenesis, disease management and prevention. To illustrate the knowledge gaps that remain to be filled in order to control dengue and achieve the WHO 2010-2020 goals.
    METHODS: An updated systematic review (2009-2019) was carried out. The databases Pubmed, Embase and The Cochrane Library were searched along with WHO and CDC guidelines.
    RESULTS: In total, 40 articles were included. Contemporary climatic and economic factors significantly contributed to the emergence of epidemic dengue. Unfortunately, CYD-TDV failed to meet safety and efficacy demands. New vaccination approaches are in the pipeline along with innovative vector-control strategies. Current anti-viral drug research focuses on repurposing drugs in addition to specific anti-dengue strategies that interfere with viral replication.
    CONCLUSION: The lack of understanding dengue pathogenesis and immunology has hampered the development of an effective vaccine. Recent research has provided new insights into the therapeutic and prophylactic approach. Implementation of complementary methods to control disease burden are required considering the socio-economic impact of this rapidly emerging global disease.
    Keywords:  dengue vaccines; dengue virus; severe dengue; signs and symptoms; therapeutics
  26. mSphere. 2020 Oct 21. pii: e00937-20. [Epub ahead of print]5(5):
    Tagliamonte MS, Yowell CA, Elbadry MA, Boncy J, Raccurt CP, Okech BA, Goss EM, Salemi M, Dame JB.
      The malaria parasite, Plasmodium falciparum, was introduced into Hispaniola and other regions of the Americas through the slave trade spanning the 16th through the 19th centuries. During this period, more than 12 million Africans were brought across the Atlantic to the Caribbean and other regions of the Americas. Since malaria is holoendemic in West Africa, a substantial percentage of these individuals carried the parasite. St. Domingue on Hispaniola, now modern-day Haiti, was a major port of disembarkation, and malaria is still actively transmitted there. We undertook a detailed study of the phylogenetics of the Haitian parasites and those from Colombia and Peru utilizing whole-genome sequencing. Principal-component and phylogenetic analyses, based upon single nucleotide polymorphisms (SNPs) in protein coding regions, indicate that, despite the potential for millions of introductions from Africa, the Haitian parasites share an ancestral relationship within a well-supported monophyletic clade with parasites from South America, while belonging to a distinct lineage. This result, in stark contrast to the historical record of parasite introductions, is best explained by a severe population bottleneck experienced by the parasites introduced into the Americas. Here, evidence is presented for targeted selection of rare African alleles in genes which are expressed in the mosquito stages of the parasite's life cycle. These genetic markers support the hypothesis that the severe population bottleneck was caused by the required adaptation of the parasite to transmission by new definitive hosts among the Anopheles (Nyssorhynchus) spp. found in the Caribbean and South America.IMPORTANCE Historical data suggest that millions of P. falciparum parasite lineages were introduced into the Americas during the trans-Atlantic slave trade, which would suggest a paraphyletic origin of the extant isolates in the Western Hemisphere. Our analyses of whole-genome variants show that the American parasites belong to a well-supported monophyletic clade. We hypothesize that the required adaptation to American vectors created a severe bottleneck, reducing the effective introduction to a few lineages. In support of this hypothesis, we discovered genes expressed in the mosquito stages of the life cycle that have alleles with multiple, high-frequency or fixed, nonsynonymous mutations in the American populations which are rarely found in African isolates. These alleles appear to be in gene products critical for transmission through the anopheline vector. Thus, these results may inform efforts to develop novel transmission-blocking vaccines by identifying parasite proteins functionally interacting with the vector that are important for successful transmission. Further, to the best of our knowledge, these are the first whole-genome data available from Haitian P. falciparum isolates. Defining the genome of these parasites provides genetic markers useful for mapping parasite populations and monitoring parasite movements/introductions.
    Keywords:  Haiti; Plasmodium falciparum; adaptive mutations; evolutionary biology; malaria; phylogenetics; vector-borne diseases
  27. Am J Trop Med Hyg. 2020 Oct 19.
    Wotodjo AN, Doucoure S, Diagne N, Sarr FD, Parola P, Gaudart J, Sokhna C.
      The occurrence of malaria resurgences could threaten progress toward elimination of the disease. This study investigated the impact of repeated renewal of long-lasting insecticide-treated net (LLIN) universal coverage on malaria resurgence over a period of 10 years of net implementation in Dielmo (Senegal). A longitudinal study was carried out in Dielmo between August 2007 and July 2018. In July 2008, LLINs were offered to all villagers through universal campaign distribution which was renewed in July 2011, August 2014, and May 2016. Malaria cases were treated with artemisinin-based combination therapy. Two resurgences of malaria occurred during the 10 years in which LLINs have been in use. Since the third renewal of the nets, malaria decreased significantly compared with the first year the nets were implemented (adjusted incidence rate ratio) (95% CI) = 0.35 (0.15-0.85), during the ninth year after net implementation). During the tenth year of net implementation, no cases of malaria were observed among the study population. The use of nets increased significantly after the third time the nets were renewed when compared with the year after the first and the second times the nets were renewed (P < 0.001). The third renewal of nets, which took place after 2 years instead of 3 years together with a higher use of LLINs especially among the young, probably prevented the occurrence of a third malaria upsurge in this village.
  28. PLoS One. 2020 ;15(10): e0240741
    Meireles BM, de Souza Sampaio V, Monteiro WM, Gonçalves MJF.
      BACKGROUND: In Brazil malaria is most frequent in the Amazon region, mainly in the Amazonas state, where it is found the most proportion of indigenous people of the whole country. It is remarkable publications about malaria in the Amazon, although information on malaria in indigenous populations is still poorly explored.OBJECTIVE: Identify factors associated with malaria in indigenous populations.
    METHODS: Cross-sectional study of positive cases of malaria in the state of Amazonas, Brazil, from 2007 to 2016. Secondary data were obtained from the Epidemiological Surveillance Information System for Malaria and from the Mortality Information System, both from Brazil. To tackle with race missing data, cases with no race fulfilled were classified according to the probable location where infection occurred. This way, was imputed indigenous race for those which the probable infection location was indigenous village (aldeia). Variables tested with race were: sex, age, schooling, microscope surveillance slide type, parasitic infection species, parasitemia level, and timeliness of treatment. Multivariate logistic regression was used.
    RESULTS: A total of 1,055,852 cases of malaria were notified in the state of Amazonas. Among the factors that associate malaria and indigenous peoples, the most significant were sex, children and high levels of parasitemia. The magnitude of Plasmodium vivax infection is higher than Plasmodium falciparum, although this parasite was more frequent in indigenous than other races. In regards to mortality, 109 deaths were registered, most of them related to P. vivax.
    CONCLUSION: The findings underscore the importance of look at indigenous people differently of other races. The associated factors highlight a profile of cases severity, because of highest parasitemia, many cases of P. falciparum although high frequency of P. vivax, and children. Furthermore, the mortality in indigenous, specially in older people is worrying.