bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒06‒28
twenty-four papers selected by
Richard Halfpenny
Staffordshire University

  1. Malar J. 2020 Jun 22. 19(1): 212
      BACKGROUND: Zanzibar provides a good case study for malaria elimination. The islands have experienced a dramatic reduction in malaria burden since the introduction of effective vector control interventions and case management. Malaria prevalence has now been maintained below 1% for the past decade and the islands can feasibly aim for elimination.METHODS: To better understand factors that may contribute to remaining low-level malaria transmission in Zanzibar, layered human behavioural and entomological research was conducted between December 2016 and December 2017 in 135 randomly selected households across six administrative wards. The study included: (1) household surveys, (2) structured household observations of nighttime activity and sleeping patterns, and (3) paired indoor and outdoor mosquito collections. Entomological and human behavioural data were integrated to provide weighted estimates of exposure to vector bites, accounting for proportions of people indoors or outdoors, and protected by insecticide-treated nets (ITNs) each hour of the night.
    RESULTS: Overall, 92% of female Anopheles mosquitoes were caught in the rainy season compared to 8% in the dry season and 72% were caught outdoors compared to 28% indoors. For individual ITN users, ITNs prevented an estimated two-thirds (66%) of exposure to vector bites and nearly three quarters (73%) of residual exposure was estimated to occur outdoors. Based on observed levels of ITN use in the study sites, the population-wide mean personal protection provided by ITNs was 42%.
    DISCUSSION/CONCLUSIONS: This study identified gaps in malaria prevention in Zanzibar with results directly applicable for improving ongoing programme activities. While overall biting risk was low, the most notable finding was that current levels of ITN use are estimated to prevent less than half of exposure to malaria vector bites. Variation in ITN use across sites and seasons suggests that additional gains could be made through targeted social and behaviour change interventions. However, even for ITN users, gaps in protection remain, with a majority of exposure to vector bites occurring outdoors before going to sleep. Supplemental interventions targeting outdoor exposure to malaria vectors, and groups that may be at increased risk of exposure to malaria vectors, should be explored.
    Keywords:  Exposure; Human behavior; Human–vector contact; Human–vector interaction; Malaria; Outdoor transmission; Residual transmission; Tanzania; Zanzibar
  2. BMC Microbiol. 2020 Jun 26. 20(1): 181
      BACKGROUND: Chikungunya (CHIKV), yellow fever (YFV) and Zika (ZIKV) viruses circulate in sylvatic transmission cycles in southeastern Senegal, where they share common hosts and vectors. All three viruses undergo periodic amplifications, during which they are detected in mosquitoes and sometimes in hosts. However, little is known about their spatio-temporal patterns in years in which they undergo concurrent amplification. The aim of this study was to describe the co-amplification of ZIKV, CHIKV, and YFV, and the daily dynamics of these arboviruses and theirs vectors within villages in southeastern Senegal.RESULTS: Mosquitoes were collected monthly from July to December 2015. Each evening, from 6 to 9 PM, landing collections were performed by teams of 3 persons working simultaneously in 70 sites situated in forest (canopy and ground), savannah, agriculture, barren, and village (indoor and outdoor) land covers. Collections within villages were continued until 6 AM. Mosquitoes were tested for virus infection by virus isolation and RT-PCR. Seventy-five mosquito pools comprising 10 mosquito species contained at least one virus. Ae. furcifer and Ae. luteocephalus were infected by all three viruses, Ae. taylori by YFV and ZIKV, and remaining seven species by only, only YFV or only ZIKV. No single mosquito pool contained more than one virus. CHIKV was the only virus detected in all land cover classes and was found in the greatest number of sampling sites (32.9%, n = 70). The proportion of sites in which more than one virus was detected was less than 6%. Ae. aegypti formosus, Ae. furcifer, Ae. luteocephalus, Ae. minutus, Ae. vittatus, and An. gambiae were found within villages. These vectors were mainly active around dusk but Ae. furcifer was collected until dawn. All viruses save ZIKV were detected indoors and outdoors, mainly around dusk. Virus positive pools were detected over 2, 3 and 4 months for YFV, CHIKV and ZIKV, respectively.
    CONCLUSION: Our data indicate that the distribution of different vector species and different arboviruses vary substantially between sites, suggesting that CHIKV, YFV, and ZIKV may have different transmission cycles in Southeastern Senegal.
    Keywords:  Amplification; Chikungunya virus; Concurrent; Mosquito vectors; Southeastern Senegal; Yellow fever virus; Zika virus
  3. Infect Genet Evol. 2020 Jun 21. pii: S1567-1348(20)30265-3. [Epub ahead of print] 104434
      Due to the rapid spread of Zika virus (ZIKV) infection after its emergence in the Americas in 2015 and its relationship with birth defects, it became declared a Public Health Emergency of International Concern (WHO). The main mechanism by which this virus circulates in nature is horizontal transmission between vectors and humans. However, it has been suggested that vertical transmission (parent to offspring infection) or venereal mosquito-mosquito transmission may have an important role in viral populations maintenance during inter-epidemic periods. In this study we evaluate the presence of ZIKV in males and females of Aedes aegypti and Ae. albopictus in Medellín, Colombia, throughout the post-epidemic period of 2017 and 2018. A total of 7986 mosquitoes Aedes sp. resting within houses were captured and grouped in 2768 pools; 146 of these were RT-PCR positive for ZIKV, of which 38 (26%) were male mosquito pools (36 of Ae. aegypti and 2 of Ae. albopictus). The partial NS5 gene was sequenced in all ZIKV PCR-positive pools to confirm the ZIKV presence throughout spatial and temporal sampling. The results suggest a vector role of ZIKV by Ae. Albopictus; and because it is well known that male mosquitoes are not hematophagous, the high rate detection of ZIKV in male Aedes mosquitoes pools supports the existence of vertical or venereal transmission in Medellín, which can contribute to ZIKV maintenance during low transmission periods. This study provides a better understanding of the population dynamics of ZIKV in an endemic region during an inter-epidemic period and supports alternative transmission pathways as a mechanism to maintain endemism of this arbovirus.
    Keywords:  Entomovirology surveillance; Male mosquitoes; Venereal transmission; Vertical transmission; Zika transmission
  4. Viruses. 2020 Jun 19. pii: E659. [Epub ahead of print]12(6):
      Zika virus (ZIKV) is a mosquito-borne pathogen that caused a large outbreak in the Americas in 2015 and 2016. The virus is currently present in tropical areas around the globe and can cause severe disease in humans, including Guillain-Barré syndrome and congenital microcephaly. The tropical yellow fever mosquito, Aedes aegypti, is the main vector in the urban transmission cycles of ZIKV. The discovery of ZIKV in wild-caught Culex mosquitoes and the ability of Culex quinquefasciatus mosquitoes to transmit ZIKV in the laboratory raised the question of whether the common house mosquito Culex pipiens, which is abundantly present in temperate regions in North America, Asia and Europe, could also be involved in ZIKV transmission. In this study, we investigated the vector competence of Cx. pipiens (biotypes molestus and pipiens) from the Netherlands for ZIKV, using Usutu virus as a control. After an infectious blood meal containing ZIKV, none of the tested mosquitoes accumulated ZIKV in the saliva, although 2% of the Cx. pipiens pipiens mosquitoes showed ZIKV-positive bodies. To test the barrier function of the mosquito midgut on virus transmission, ZIKV was forced into Cx. pipiens mosquitoes by intrathoracic injection, resulting in 74% (molestus) and 78% (pipiens) ZIKV-positive bodies. Strikingly, 14% (molestus) and 7% (pipiens) of the tested mosquitoes accumulated ZIKV in the saliva after injection. This is the first demonstration of ZIKV accumulation in the saliva of Cx. pipiens upon forced infection. Nevertheless, a strong midgut barrier restricted virus dissemination in the mosquito after oral exposure and we, therefore, consider Cx. pipiens as a highly inefficient vector for ZIKV.
    Keywords:  Culex pipiens; Zika virus; arbovirus; flavivirus; midgut barrier; the Netherlands; vector competence
  5. PLoS Negl Trop Dis. 2020 Jun 22. 14(6): e0008350
      BACKGROUND: The arboviral vector Aedes albopictus became established on all continents except Antarctica in the past 50 years. A consequence of its rapid global invasion is the transmission of diseases previously confined to the tropics and subtropics occurring in temperate regions of the world, including the re-emergence of chikungunya and dengue in Europe. Application of pyrethroids is among the most widely-used interventions for vector control, especially in the presence of an arboviral outbreak. Studies are emerging that reveal phenotypic resistance and monitor mutations at the target site, the para sodium channel gene, primarily on a local scale.METHODS: A total of 512 Ae. albopictus mosquitoes from twelve geographic sites, including those from the native home range and invaded areas, were sampled between 2011 and 2018, and were analyzed at five codons of the para sodium channel gene with mutations predictive of resistance phenotype. Additionally, to test for the origin of unique kdr mutations in Mexico, we analyzed the genetic connectivity of southern Mexico mosquitoes with mosquitoes from home range, the Reunion Island, America and Europe.
    RESULTS: We detected mutations at all tested positions of the para sodium channel gene, with heterozygotes predominating and rare instance of double mutants. We observed an increase in the distribution and frequency of F1534C/L/S mutations in the ancestral China population and populations in the Mediterranean Greece, the appearance of the V1016G/I mutations as early as 2011 in Italy and mutations at position 410 and 989 in Mexico. The analyses of the distribution pattern of kdr alleles and haplotype network analyses showed evidence for multiple origins of all kdr mutations.
    CONCLUSIONS: Here we provide the most-up-to-date survey on the geographic and temporal distribution of pyrethroid-predictive mutations in Ae. albopictus by combining kdr genotyping on current and historical samples with published data. While we confirm low levels of pyrethroid resistance in most analyzed samples, we find increasing frequencies of F1534C/S and V1016G in China and Greece or Italy, respectively. The observed patterns of kdr allele distribution support the hypothesis that on site emergence of resistance has contributed more than spread of resistance through mosquito migration/invasions to the current widespread of kdr alleles, emphasizing the importance of local surveillance programs and resistance management.
  6. J Virol. 2020 Jun 24. pii: JVI.00343-20. [Epub ahead of print]
      Zika virus (ZIKV) is an emerging flavivirus mainly transmitted by mosquitoes that represents a global health threat. A common feature of flavivirus infected cells is the accumulation of viral non-coding subgenomic RNAs by partial degradation of the viral genome, known as sfRNAs, involved in immune evasion and pathogenesis. Although a great effort is being placed to understand the mechanism by which these sfRNAs function during infection, the picture of how they work is still incomplete. In this study, we developed new genetic tools to dissect the functions of ZIKV RNA structures for viral replication and sfRNA production in mosquito and human hosts. ZIKV infections mostly accumulate two kinds of sfRNAs, sfRNA1 and sfRNA2, by stalling genome degradation upstream of duplicated stem loops (SLI and SLII) of the viral 3'UTR. Although the two SLs share conserved sequences and structures, different functions have been found for ZIKV replication in human and mosquito cells. While both SLs are enhancers for viral infection in human cells, they play opposite roles in the mosquito host. The dissection of determinants for sfRNA formation indicated a strong cooperativity between SLI and SLII, supporting a high order organization of this region of the 3'UTR. Using recombinant ZIKV with different SLI and SLII arrangements, which produce different types of sfRNAs or lack the ability to generate these molecules, revealed that at least one sfRNA was necessary for efficient infection and transmission in Aedes aegypti mosquitoes. Importantly, we demonstrate an absolute requirement of sfRNAs for ZIKV propagation in human cells. In this regard, viruses lacking sfRNAs, constructed by deletion of the region containing SLI and SLII, were able to infect human cells but the infection was rapidly cleared by antiviral responses. Our findings are unique for ZIKV since previous studies with other flaviviruses with deletions of analogous regions of the genome, including dengue and West Nile viruses, accumulated distinct species of sfRNAs and were infectious in human cells. We conclude that flaviviruses share common strategies for sfRNA generation, but they have evolved mechanisms to produce different kinds of these RNAs to accomplish virus-specific functions.IMPORTANCE Flaviviruses are important emerging and reemerging human pathogens. Understanding the molecular mechanisms for viral replication and evasion of host antiviral responses are relevant to develop control strategies. Flavivirus infections produce viral non-coding RNAs, known as sfRNAs, involved in viral replication and pathogenesis. Here, we dissected molecular determinants for Zika virus sfRNA generation in the two natural hosts, human cells and mosquitoes. We found that two RNA structures of the viral 3'UTR operate in a cooperative manner to produce two species of sfRNAs, and that the deletion of these elements have a profoundly different impact on viral replication in the two hosts. Generation of at least one sfRNA was necessary for efficient Zika virus infection of Aedes aegypti mosquitoes. Moreover, recombinant viruses with different 3'UTR arrangements revealed an essential role of sfRNAs for productive infection in human cells. In summary, we define molecular requirements for Zika virus sfRNA accumulation and provide new ideas of how flavivirus RNA structures have evolved to succeed in different hosts.
  7. Malar J. 2020 Jun 23. 19(1): 219
      BACKGROUND: In rural south-eastern Tanzania, Anopheles funestus is a major malaria vector, and has been implicated in nearly 90% of all infective bites. Unfortunately, little is known about the natural ecological requirements and survival strategies of this mosquito species.METHODS: Potential mosquito aquatic habitats were systematically searched along 1000 m transects from the centres of six villages in south-eastern Tanzania. All water bodies were geo-referenced, characterized and examined for presence of Anopheles larvae using standard 350 mLs dippers or 10 L buckets. Larvae were collected for rearing, and the emergent adults identified to confirm habitats containing An. funestus.
    RESULTS: One hundred and eleven habitats were identified and assessed from the first five villages (all < 300 m altitude). Of these, 36 (32.4%) had An. funestus co-occurring with other mosquito species. Another 47 (42.3%) had other Anopheles species and/or culicines, but not An. funestus, and 28 (25.2%) had no mosquitoes. There were three main habitat types occupied by An. funestus, namely: (a) small spring-fed pools with well-defined perimeters (36.1%), (b) medium-sized natural ponds retaining water most of the year (16.7%), and (c) slow-moving waters along river tributaries (47.2%). The habitats generally had clear waters with emergent surface vegetation, depths > 0.5 m and distances < 100 m from human dwellings. They were permanent or semi-permanent, retaining water most of the year. Water temperatures ranged from 25.2 to 28.8 °C, pH from 6.5 to 6.7, turbidity from 26.6 to 54.8 NTU and total dissolved solids from 60.5 to 80.3 mg/L. In the sixth village (altitude > 400 m), very high densities of An. funestus were found along rivers with slow-moving clear waters and emergent vegetation.
    CONCLUSION: This study has documented the diversity and key characteristics of aquatic habitats of An. funestus across villages in south-eastern Tanzania, and will form an important basis for further studies to improve malaria control. The observations suggest that An. funestus habitats in the area can indeed be described as fixed, few and findable based on their unique characteristics. Future studies should investigate the potential of targeting these habitats with larviciding or larval source management to complement malaria control efforts in areas dominated by this vector species.
    Keywords:  Anopheles funestus; Ifakara; Larval source management; Larviciding; Malaria; Tanzania
  8. J Med Entomol. 2020 Jun 23. pii: tjaa117. [Epub ahead of print]
      Mosquito-borne pathogens contribute significantly to the global burden of infectious diseases and are a continuing public health concern in the United States. Blood feeding by vector mosquitoes is a critical step in the transmission of human pathogens. Continuous surveillance of mosquito feeding patterns, especially in major population centers, is necessary for sustainable, effective control strategies. To better understand female feeding habits in Harris County, TX, we trapped mosquitoes from various locations, distributed among urban and semi-urban environments. Bloodmeal hosts were determined using a cytochrome C oxidase I DNA barcoding strategy. We identified a diverse array of vertebrate hosts with a high degree of avian host utilization, most surprisingly from anthropophilic species like Aedes aegypti (L.). We also detected sequences from two different vertebrate hosts in about half of specimens examined, suggesting that multiple bloodmeals had been acquired in the same feeding cycle by a sizable fraction of females in both urban and semi-urban locations. The high proportion of feeding on domestic chickens may indicate that a significant number of homeowners are rearing chickens within close proximity to study trap sites. As non-amplifying hosts, chickens may have a diluting effect on West Nile virus, as well as a zooprophylactic effect in their immediate vicinities. Ultimately, spatial and temporal host utilization patterns add insight into potential disease transmission dynamics, thereby informing vector control strategies in Harris County and other metropolitan areas.
    Keywords:  Harris County; blood feeding; host utilization; mosquito; zoonotic disease
  9. Am J Trop Med Hyg. 2020 Jun 22.
      Zoonotic pathogens such as arboviruses have comprised a significant proportion of emerging infectious diseases in humans. The role of wildlife species as reservoirs for arboviruses is poorly understood, especially in endemic areas such as Southeast Asia. This study aims to determine the exposure history of different macaque species from national parks in Thailand to mosquito-borne flaviviruses and alphavirus by testing the serum samples collected from 25 northern pigtailed macaques, 33 stump-tailed macaques, and 4 long-tailed macaques for the presence of antibodies against dengue, Zika, and chikungunya viruses by plaque reduction neutralization assay. Specific neutralizing antibodies against Dengue virus (DENV1-4) and Zika virus (ZIKV) were mainly found in stump-tailed macaques, whereas neutralizing antibody titers were not detected in long-tailed macaques and pigtailed macaques as determined by 90% plaque reduction neutralization assay (PRNT90). One long-tailed macaque captured from the south of Thailand exhibited antibody titers against chikungunya virus (CHIKV), suggesting enzootic of this virus to nonhuman primates (NHPs) in Thailand. Encroachment of human settlements into the forest has increased the interface that exposes humans to zoonotic pathogens such as arboviruses found in monkeys. Nonhuman primates living in different regions of Thailand showed different patterns of arboviral infections. The presence of neutralizing antibodies among wild monkeys in Thailand strongly suggests the existence of sylvatic cycles for DENV, ZIKV, and CHIKV in Thailand. The transmission of dengue, Zika, and chikungunya viruses among wild macaques may have important public health implications.
  10. PLoS Negl Trop Dis. 2020 Jun 23. 14(6): e0008433
      Mosquitoes are of major importance to human and animal health due to their ability to transmit various pathogens. In Europe the role of mosquitoes in public health has increased with the introduction of alien Aedes mosquitoes such as the Asian tiger mosquito, Aedes albopictus; the Asian bush mosquito, Ae. japonicus; and Ae. koreicus. In Austria, Ae. japonicus has established populations in various regions of the country. Aedes albopictus is not known to overwinter in Austria, although isolated findings of eggs and adult female mosquitoes have been previously reported, especially in Tyrol. Aedes koreicus had not so far been found in Austria. Within the framework of an alien mosquito surveillance program in the Austrian province of Tyrol, ovitraps were set up weekly from May to October, 2018, at 67 sites- 17 in East Tyrol and 50 in North Tyrol. Sampling was performed at highways and at urban and rural areas. DNA obtained from mosquito eggs was barcoded using molecular techniques and sequences were analysed to species level. Eggs of alien Aedes species were found at 18 out of 67 sites (27%). Both Ae. albopictus and Ae. japonicus were documented at highways and urban areas in both East and North Tyrol. Aedes koreicus was found in East Tyrol. During this mosquito surveillance program, eggs of Ae. albopictus, Ae. japonicus, and Ae. koreicus were documented in the Austrian province of Tyrol. These findings not only show highways to be points of entry, but also point to possible establishment processes of Ae. japonicus in Tyrol. Moreover, Ae. koreicus was documented in Austria for the first time.
  11. Malar J. 2020 Jun 23. 19(1): 221
      BACKGROUND: Over the last two decades, there has been remarkable progress in malaria control in sub-Saharan Africa, due mainly to the massive deployment of long-lasting insecticidal nets and indoor residual spraying. Despite these gains, it is clear that in many situations, additional interventions are needed to further reduce malaria transmission. The World Health Organization (WHO) has promoted the Integrated Vector Management (IVM) approach through its Global Vector Control Response 2017-2030. However, prior roll-out of larval source management (LSM) as part of IVM, knowledge on ecology of larval aquatic habitats is required.METHODS: Aquatic habitats colonized by immature Anopheles and culicines vectors were characterized at three sites of low, medium and high malaria transmission in Uganda from October 2011 to June 2015. Larval surveys were conducted along transects in each site and aquatic habitats described according to type and size. Immature Anopheles, culicines and pupae from the described habitats were sampled using standard dipping methods to determine larval and pupae densities. Larvae were identified as anopheline or culicine, and counted. Pupae were not identified further. Binary logistic regression analysis was used to identify factors associated with the presence of immature Anopheles and culicines in each site.
    RESULTS: A total of 1205 larval aquatic habitats were surveyed and yielded a total of 17,028 anopheline larvae, 26,958 culicine larvae and 1189 pupae. Peaks in larval abundance occurred in all sites in March-May and August-October coinciding with the rainy seasons. Anopheles larvae were found in 52.4% (n = 251) of aquatic habitats in Tororo, a site of high transmission, 41.9% (n = 536) of habitats in Kanungu, a site with moderate malaria transmission, and 15.8% (n = 418) in Jinja, a site with low malaria transmission. The odds of finding larvae was highest in rice fields compared to pools in both Tororo (odds ratio, OR = 4.21, 95% CI 1.22-14.56, p = 0.02) and Kanungu (OR = 2.14, 95% CI 1.12-4.07, p = 0.02), while in Jinja the odd were highest in containers (OR = 4.55, 95% CI = 1.09-19.14, p = 0.03). In Kanungu, larvae were less likely to be found in containers compared to pools (OR = 0.26, 95% CI 0.09-0.66, p = 0.008) and river fringe (OR = 0.19, 95% CI 0.07-0.52, p = 0.001). Medium sized habitats were associated with high odds of finding larvae compared to small habitats (OR = 3.59, 95% CI 1.18-14.19, p = 0.039).
    CONCLUSIONS: These findings show that immature Anopheles and culicines were common in areas of high and moderate transmission but were rare in areas of low transmission. Although immature Anopheles and culicines were found in all types of water bodies, they were most common in rice fields and less common in open drains and in river fringes. Methods are needed to reduce the aquatic stages of anopheline mosquitoes in human-made habitats, particularly rice fields.
    Keywords:  Anopheles; Anopheline; Aquatic habitats; Culicine; Larvae; Malaria; Pupae; Uganda
  12. Acta Trop. 2020 Jun 19. pii: S0001-706X(20)30665-3. [Epub ahead of print] 105593
      Culicidae comprises more than 3,500 species, some of which are responsible for the spread of various human diseases, causing millions of deaths worldwide. Correct identification of these species is essential for the development of surveillance and control strategies. The most common method of mosquito identification is based on specific traits of the external morphology of species. However, identification of mosquitoes by morphological characters can be inaccurate or even unfeasible if the specimen is damaged or there is a lack of distinguishing features, as in the case of cryptic species complexes. Wing geometric morphometrics is a reliable, affordable tool for the identification of mosquito species, including sibling species. More importantly, it can be used in addition to both traditional morphologic identification methods as well as genetic approaches. Here, wing geometric morphometrics was used to identify sixteen mosquito species from eight genera: Aedes, Coquillettidia, Culex, Limatus, Mansonia, Psorophora, Runchomyia, and Wyeomyia. The 390 specimens used here were collected in São Paulo, Brazil using CDC traps, aspiration, and Shannon traps. Allometry was assessed by multivariate regression of the Procrustes coordinates on centroid size followed by canonical variate analysis and a pairwise cross-validated reclassification test. A Neighbor-Joining tree based on Mahalanobis distances was constructed with 1,000 bootstrap replicates using MorphoJ 1.02 and Past 2.17c. The canonical variate analysis of genera resulted in distinct clusters for Culex, Limatus, and Psorophora and partial overlapping between Aedes, Coquilettidia, and Mansonia, and between Runchomyia and Wyeomyia. Pairwise cross-validated reclassification tests indicated that genera were identified with an accuracy of at least 99% and subgenera with a mean accuracy of 96% and that in 160 of the 240 possible comparisons species were identified with an accuracy of 100%. Our results show that the eight genera in the study were correctly distinguished by wing shape, as were subgenera and most species, demonstrating that wing geometric morphometrics can be used for the identification of the mosquito species studied here.
    Keywords:  Culicidae; neglected species; wing geometric morphometrics
  13. PLoS Negl Trop Dis. 2020 Jun 22. 14(6): e0007870
      Emerging mosquito-borne viruses like Zika, dengue, and chikungunya pose a major threat to public health, especially in low-income regions of Central and South America, southeast Asia, and the Caribbean. Outbreaks of these diseases are likely to have long-term social and economic consequences due to Zika-induced congenital microcephaly and other complications. Larval control of the container-inhabiting mosquitoes that transmit these infections is an important tool for mitigating outbreaks. However, metapopulation theory suggests that spatiotemporally uneven larvicide treatment can impede control effectiveness, as recolonization compensates for mortality within patches. Coordinating the timing of treatment among patches could therefore substantially improve epidemic control, but we must also consider economic constraints, since coordination may have costs that divert resources from treatment. To inform practical disease management strategies, we ask how coordination among neighbors in the timing of mosquito control efforts influences the size of a mosquito-borne infectious disease outbreak under the realistic assumption that coordination has costs. Using an SIR (Susceptible-Infectious-Recovered)/metapopulation model of mosquito and disease dynamics, we examine whether sharing surveillance information and coordinating larvicide treatment among neighboring patches reduces human infections when incorporating coordination costs. We examine how different types of coordination costs and different surveillance methods jointly influence the effectiveness of larval control. We find that the effect of coordination depends on both costs and the type of surveillance used to inform treatment. With epidemiological surveillance, coordination improves disease outcomes, even when costly. With demographic surveillance, coordination either improves or hampers disease control, depending on the type of costs and surveillance sensitivity. Our results suggest coordination among neighbors can improve management of mosquito-borne epidemics under many, but not all, assumptions about costs. Therefore, estimating coordination costs is an important step for most effectively applying metapopulation theory to strategies for managing outbreaks of mosquito-borne viral infections.
  14. Pest Manag Sci. 2020 Jun 27.
      BACKGROUND: Understanding pest incursion pathways is critical for preventing new invasions and for stopping the transfer of alleles that reduce the efficacy of local control methods. The mosquitoes Aedes albopictus (Skuse) and Ae. aegypti (Linnaeus) are both highly invasive disease vectors, and through a series of ongoing international incursions are continuing to colonise new regions and spread insecticide resistance alleles among established populations. This study uses high-resolution molecular markers and a set of 241 reference genotypes to trace incursion pathways of Ae. albopictus into mainland Australia, where no successful invasions have yet been observed. We contrast these results with incursion pathways of Ae. aegypti, investigated previously.RESULTS: Assignments successful identified China, Japan, Singapore and Taiwan as source locations. Incursion pathways of Ae. albopictus were entirely different to those of Ae. aegypti, despite broad sympatry of these species throughout the Indo-Pacific region. Incursions of Ae. albopictus appeared to have come predominantly along marine routes from key trading locations, while Ae. aegypti was mostly linked to aerial routes from tourism hotspots.
    CONCLUSION: These results demonstrate how genomics can help decipher otherwise cryptic incursion pathways. The inclusion of reference genotypes from the Americas may help resolve some unsuccessful assignments. While many congeneric taxa will share common incursion pathways, this study highlights that this is not always the case, and incursion pathways of important taxa should be specifically investigated. Species differences in aerial and marine incursion rates may reflect the efficacy of ongoing control programs such as aircraft disinsection. This article is protected by copyright. All rights reserved.
    Keywords:  Aedes aegypti; Aedes albopictus; assignment tests; biological invasions; genome-wide SNPs; incursion pathways
  15. ScientificWorldJournal. 2020 ;2020 7620389
      Reliable sources of CO2 that are relatively cheap, obtainable, and easy to sustain are immediately required for scaling up of odor-baited mosquito surveillance and control devices. Several odor-baited devices are in the pipeline; however, their scale-up against residual malaria transmission, particularly in resource poor areas, is limited by the unavailability of reliable sources of CO2 and reliance on electrical power sources among other factors. We evaluated the use of granular cyclopentanone as an alternative to artificial or yeast fermentation-produced CO2 in passive outdoor host seeking device (POHD). Experiments were conducted against semifield reared An. arabiensis within the semifield system (SFS) at Ifakara Health Institute. Mosquitoes were tested against odor-baited POHDs augmented with yeast fermentation-produced CO2, granular cyclopentanone, attractive blends (Mbita or Ifakara), or their combinations. An insecticide, bendiocarb, was a killing agent used as a proxy for marking the mosquitoes visit the POHDs. Relative attractiveness of different treatment combinations was compared based on the proportion of dead mosquitoes that visited the POHD. The POHD augmented with granules of cyclopentanone alone was attractive to An. arabiensis as much as, or more than, POHDs augmented with yeast fermentation-produced CO2. The POHD baited with CO2 attracted more mosquitoes than those POHDs baited with synthetic blends alone; when these blends are combined with CO2, they attracted more mosquitoes than individual blends. More importantly, such POHDs baited with cyclopentanone attracted far greater proportion of mosquitoes than the POHD baited with either Mbita or Ifakara blend alone. The granular cyclopentanone strongly enhanced/potentiated the attractiveness of POHD baited with Mbita blends against mosquitoes compared to that of POHD baited with Ifakara blend. Moreover, the granular cyclopentanone retained its residual activity against An. arabiensis for up to 2 months after application particularly when used in combination with Mbita blend. In conclusion, this study demonstrates that cyclopentanone granules have the potential to substitute sources of CO2 in outdoor-based surveillance and control devices, thus warranting evaluation of such alternative under realistic field conditions.
  16. J Med Entomol. 2020 Jun 22. pii: tjaa118. [Epub ahead of print]
      The impact of increasing resistance of mosquitoes to conventional pesticides has led to investigate various unique tools and pest control strategies. Herein, we assessed the potency of flupyradifurone, a novel pesticide, on fourth instar larvae of Culex quinquefasciatus Say. Further, we evaluated the synergistic action of piperonyl butoxide (PBO) and the octopamine receptor agonists (OR agonists) chlordimeform (CDM) and amitraz (AMZ) on the toxicity of flupyradifurone in comparison with sulfoxaflor and nitenpyram to increase their toxicity on Cx. quinquefasciatus. Results demonstrated that flupyradifurone was the most potent pesticide followed by sulfoxaflor and nitenpyram. Further, the synergetic effect of PBO, CDM, and AMZ was significant for all selected pesticides especially flupyradifurone. However, AMZ had the most significant effect in combination with the selected pesticides followed by CDM and PBO. The toxicity of the pesticides was time-dependent and increased over time from 24, 48, to 72 h of exposure in all experiments. The results indicate that flupyradifurone is a promising component in future mosquito control programs.
    Keywords:   Culex quinquefasciatus ; flupyradifurone; mosquito control; octopamine receptor agonists (OR agonists); piperonyl butoxide (PBO)
  17. Commun Biol. 2020 Jun 24. 3(1): 326
      The mosquito Aedes albopictus is one of the most dangerous invasive species. Its worldwide spread has created health concerns as it is a major vector of arboviruses of public health significance such as chikungunya (CHIKV). Dynamics of different genetic backgrounds and admixture events may have impacted competence for CHIKV in adventive populations. Using microsatellites, we infer the genetic structure of populations across the expansion areas that we then associate with their competence for different CHIKV genotypes. Here we show that the demographic history of Ae. albopictus populations is a consequence of rapid complex patterns of historical lineage diversification and divergence that influenced their competence for CHIKV. The history of adventive populations is associated with CHIKV genotypes in a genotype-by-genotype interaction that impacts their vector competence. Thus, knowledge of the demographic history and vector competence of invasive mosquitoes is pivotal for assessing the risk of arbovirus outbreaks in newly colonized areas.
  18. Environ Sci Pollut Res Int. 2020 Jun 23.
      The recent outbreaks of mosquito-borne diseases highlighted the pivotal importance of mosquito vector control in tropical areas worldwide. Several strategies have been developed to control vector populations and disease transmission in endemic areas. The steps to obtain natural active compounds involve the pre-selection in a biological model and subsequently evaluation on specific models. The present study reports the evaluation of 35 extracts, fractions, and essential oils obtained from five species from the Annonaceae family on Artemia salina and Culex quinquefasciatus. The A. salina results were used as a pre-screening for larvicidal test about mosquitoes. A correlation of biological activity in both bioassays was observed for the hydroethanolic extracts and their respective hexane and chloroform fractions of the leaves of Annona species, except A. nutans. The same correlation was also observed for all tested essential oils and petroleum ether extracts from Duguetia species. It was possible to limit an interval of lethality about A. salina, which has a corresponding range to the larvicidal test against the mosquito. The main components present in D. lanceolata essential oil or enriched fraction were α-selinene, aristolochene, (E)-caryophyllene, and (E)-calamenene. For D. furfuracea, the main components present of the underground parts were (E)-asarone, 2,4,5-trimethoxystyrene, spathulenol, and bicyclogermacrene for aerial parts. The A. salina test could be used as a model for the pre-screening of larvicidal activity.
    Keywords:  (E)-asarone; Annona; Artemia salina; Duguetia; Essential oil; Extract
  19. Pathogens. 2020 Jun 20. pii: E491. [Epub ahead of print]9(6):
      The dynamic of arbovirus vectors such as Aedes aegypti and Ae. albopictus remains poorly understood in large cities in central Africa. Here, we compared the larval ecology, geographical distribution and degree of infestation of Ae. aegypti and Ae. albopictus in Yaoundé, the capital city of Cameroon, and estimated their Stegomyia indices revealing a significant potential risk of arbovirus transmission. An entomological survey was conducted in April-May 2018 in a cluster of houses randomly selected. Each selected house was inspected, the number of inhabitants was recorded, and potential and positive containers for Aedes were characterized. Stegomyia and pupae-based indices were estimated. Overall, 447 houses and 954 containers were inspected comprising 10,801 immature stages of Aedes with 84.95% of Ae. albopictus and 15.05% of Ae. aegypti. Both species bred mainly in discarded tanks and used tyres, associated with turbid water and the presence of plant debris inside containers. Aedes albopictus was the most prevalent species in almost all neighbourhoods. The house index, Breteau index, and container index were higher for Ae. albopictus (38.26%, 71.81%, and 29.61%) compared to those of Ae. aegypti (25.73%, 40.93%, and 16.88%). These indices are high compared to the thresholds established by Pan American Health Organization and World Health Organization, which suggests a high potential risk of arbovirus transmission.
    Keywords:  Aedes aegypti; Aedes albopictus; Cameroon; Stegomyia indices; arbovirus
  20. Curr Opin Virol. 2020 Jun 19. pii: S1879-6257(20)30022-5. [Epub ahead of print]40 41-47
      Climate change is leading to increases in global temperatures and erratic precipitation patterns, both of which are contributing to the expansion of mosquito-borne arboviruses and the populations of the mosquitos that vector them. Herein, we review recent evidence of emergence and expansion of arboviruses transmitted by Aedes mosquitos that has been driven in part by environmental changes. We present as a case study of recent work from Córdoba, Argentina, where dengue has been actively emerging in the past decade. We review recent empirical and modeling studies that aim to understand the impact of climate on future expansion of arboviruses, and we highlight gaps in empirical studies linking climate to arbovirus transmission at regional levels.
  21. Geospat Health. 2020 Jun 17. 15(1):
      Dengue is a global public health problem. The Dengue Virus (DENV) serotypes are transmitted by an Aedes aegypti mosquito. Vector control is among the primary methods to prevent the disease, especially in tropical countries. This study aimed to analyze the spatial distribution of dengue and its relationship with social inequalities using spatial modelling. An ecological study with temporal and spatial analysis was conducted in the state of Sergipe, Northeast Brazil, over a period of 18 years. Spatial modelling was used to determine the influence of space on dengue incidence and social inequalities. The epidemic rates in 2008, 2012, and 2015 were identified. Spatial modelling explained 40% of the influence of social inequalities on dengue incidence in the state. The main social inequalities related to the occurrence of dengue were the percentage of people living in extreme poverty and inadequate sanitation. The epidemic situation even increased the risk of dengue in the population of the state of Sergipe. These results demonstrate the potential of spatial modelling in determining the factors associated with dengue epidemics and are useful in planning the intersectoral public health policies.
  22. Neotrop Entomol. 2020 Jun 25.
      The oviposition behavior of mosquitoes varies between species. We documented the unusual mechanism of egg laying in the mosquito Sabethes albiprivus Theobald with the aid of high speed video recordings in the laboratory. A sapucaia (Lecythis pisonis Camb.) nut oviposition trap, described herein, was used to simulate a tree hole with a small opening, which is the natural larval habitat of Sa. albiprivus. We showed that females approach the opening and perform a sequence of rapid, short up-and-down flights before egg laying. At this time, the egg is already visible externally, being held at the very tip of the abdomen. Females catapult one egg at a time by rapidly curling their abdomen downward, sending the egg through the opening while their legs are positioned in different configurations throughout the event. The estimated velocity of the catapulted eggs was almost 1 m/s.
    Keywords:  Sabethes mosquitoes; egg-laying behavior; oviposition; sylvatic mosquitoes; tree-hole
  23. Pathog Glob Health. 2020 Jun 25. 1-15
      Despite being one of the continents with the least greenhouse gas emissions, no continent is being struck as severely by climate change (CC) as Africa. Mosquito-borne diseases (MBD) cause major human diseases in this continent. Current knowledge suggests that MBD range could expand dramatically in response to CC. This study aimed at assessing the relationship between CC and MBD in Africa. Methods For this purpose, a systematic peer review was carried out, considering all articles indexed in PubMed, Scopus, Embase and CENTRAL. Search terms referring to MBD, CC and environmental factors were screened in title, abstract and keywords.Results A total of twenty-nine studies were included, most of them on malaria (61%), being Anopheles spp. (61%) the most commonly analyzed vector, mainly in Eastern Africa (48%). Seventy-nine percent of these studies were based on predictive models. Seventy-two percent of the reviewed studies considered that CC impacts on MBD epidemiology. MBD prevalence will increase according to 69% of the studies while 17% predicted a decrease. MBD expansion throughout the continent was also predicted. Most studies showed a positive relationship between observed or predicted results and CC. However, there was a great heterogeneity in methodologies and a tendency to reductionism, not integrating other variables that interact with both the environment and MBD. In addition, most results have not yet been tested. A global health approach is desirable in this kind of research. Nevertheless, we cannot wait for science to approve something that needs to be addressed now to avoid greater effects in the future.
    Keywords:  Africa; Mosquito-borne diseases; climate change; dengue; environmental factors; malaria
  24. Cad Saude Publica. 2020 ;pii: S0102-311X2020000605003. [Epub ahead of print]36(6): e00110519
      The proliferation of arboviruses and their vectors is influenced by a complex interplay between vector, environment and human behaviors. The aim of this work is to analyze the influence of socio-environmental determinants on knowledge and practices regarding arboviruses transmission, among the residents of three communities on the southern border of Mexico. Between June 2017 and August 2018, a set of 149 households from three communities of Tapachula (Chiapas) and Villahermosa (Tabasco) were covered. This study consists of the application of a community prevention project. Different surveys and methodological approaches were used. Associations between socio-environmental determinants and knowledge and practices for arboviruses transmission control were estimated by odds ratio. Logistic regression and qualitative techniques were used. Although around 75% of households had an adequate knowledge about arboviruses' origin and transmission, only 30% of them adopted adequate practices. Domestic risk practices were associated with serious deficiencies in water and sanitation services. Furthermore, a perception of greater risk and difficulty in complying with preventive measures were detected. An adequate knowledge does not necessarily lead to adequate prevention practices. Intermediate social determinants influence on the persistence of risk behaviors for arboviruses proliferation. Addressing such related aspects requires the achievement of an effective and sustainable vector management.