bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒10‒18
twenty papers selected by
Richard Halfpenny
Staffordshire University

  1. Insects. 2020 Oct 13. pii: E699. [Epub ahead of print]11(10):
    Sanders JD, Talley JL, Frazier AE, Noden BH.
      As mosquito-borne diseases are a growing human health concern in the United States, the distribution and potential arbovirus risk from container-breeding Aedes mosquitoes is understudied in the southern Great Plains. The aim of the study was to assess landscape and anthropogenic factors associated with encountering adult container-breeding mosquitoes in small cities in southern Oklahoma. Collections were carried out over a 10 week period from June to August 2017 along two geographical transects, each consisting of three cities, equally distant from the Red River/Texas border. Mosquitoes were collected weekly using two trap types along with data for 13 landscape, vegetation, and anthropogenic variables. After five rounds of collection, 6628 female mosquitoes were collected over 2110 trap-nights involving 242 commercial or residential sites in six cities. Of the mosquitoes collected, 80% consisted of container-breeding species: Aedes albopictus (72%), Culex pipiens complex (16%) and Aedes aegypti (8%). Regionally, Aedes aegypti was more likely present in cities closest to the Texas border while Ae. albopictus was spread throughout the region. In general, Ae. aegypti and Ae. albopictus were significantly more present in sites featuring no or low vegetation and residential sites. Variables associated with Ae. albopictus presence and abundance varied between cities and highlighted the urban nature of the species. The study highlighted the distribution of Ae. aegypti geographically and within the urban context, indicated potential habitat preferences of container-breeding mosquito species in small towns, and demonstrated the usefulness of Gravid Aedes traps (GAT) traps for monitoring Aedes populations in urban habitats in small cities.
    Keywords:  Aedes; Great Plains; Oklahoma; mosquito; urban
  2. PLoS Pathog. 2020 Oct 14. 16(10): e1008951
    Kuo L, Jaeger AS, Banker EM, Bialosuknia SM, Mathias N, Payne AF, Kramer LD, Aliota MT, Ciota AT.
      Both mosquito species-specific differences and virus strain -specific differences impact vector competence. Previous results in our laboratory with individual populations of N. American mosquitoes support studies suggesting Aedes aegypti are more competent than Ae. albopictus for American Zika virus (ZIKV) strains and demonstrate that U.S. Ae. albopictus have higher competence for an ancestral Asian ZIKV strain. A982V, an amino acid substitution in the NS1 gene acquired prior to the American outbreak, has been shown to increase competence in Ae. aegypti. We hypothesized that variability in the NS1 could therefore contribute to species-specific differences and developed a reverse genetics system based on a 2016 ZIKV isolate from Honduras (ZIKV-WTic) to evaluate the phenotypic correlates of individual amino acid substitutions. In addition to A982V, we evaluated G894A, which was acquired during circulation in the Americas. Reversion of 982 and 894 to ancestral residues increased infectivity, transmissibility and viral loads in Ae. albopictus but had no effect on competence or replication in Ae. aegypti. In addition, while host cell-specific differences in NS1 secretion were measured, with significantly higher secretion in mammalian cells relative to mosquito cells, strain-specific differences in secretion were not detected, despite previous reports. These results demonstrate that individual mutations in NS1 can influence competence in a species-specific manner independent of differences in NS1 secretion and further indicate that ancestral NS1 residues confer increased competence in Ae. albopictus. Lastly, experimental infections of Ifnar1-/- mice demonstrated that these NS1 substitutions can influence viral replication in the host and, specifically, that G894A could represent a compensatory change following a fitness loss from A982V with some viral genetic backgrounds. Together these data suggest a possible role for epistatic interactions in ZIKV fitness in invertebrate and vertebrate hosts and demonstrate that strains with increased transmission potential in U.S. Ae. albopictus could emerge.
  3. PLoS Negl Trop Dis. 2020 Oct 15. 14(10): e0008776
    Lai Z, Zhou T, Liu S, Zhou J, Xu Y, Gu J, Yan G, Chen XG.
      BACKGROUND: Zika virus (ZIKV) is an arthropod-borne flavivirus transmitted by Aedes mosquitoes. Aedes albopictus is an important vector of ZIKV worldwide. To date, most experiments have focused on the vertical transmission of ZIKV in Ae. aegypti, while studies on Ae. albopictus are very limited. To explore vertical transmission in Ae. albopictus, a series of laboratory studies were carried out.METHODOLOGY/PRINCIPAL FINDINGS: In this study, Ae. albopictus were blood-fed with ZIKV-infectious blood, and the ovaries and offspring viral infection rates were analyzed by reverse transcription PCR (RT-PCR), real-time reverse transcription PCR (RT-qPCR) and immunohistochemistry (IHC). ZIKV was detected in the ovaries and oviposited eggs in two gonotrophic cycles. The minimum filial egg infection rates in two gonotrophic cycles were 2.06% and 0.69%, and the effective population transmission rate was 1.87%. The hatching, pupation, and emergence rates of infected offspring were not significantly different from those of uninfected offspring, indicating that ZIKV did not prevent the offspring from completing the growth and development process. ZIKV was detected in three of thirteen C57BL/6 suckling mice bitten by ZIKV-positive F1 females, and the viremia persisted for at least seven days.
    CONCLUSIONS/SIGNIFICANCE: ZIKV can be vertically transmitted in Ae. albopictus via transovarial transmission. The vertical transmission rates in F1 eggs and adults were 2.06% and 1.87%, respectively. Even though the vertical transmission rates were low, the female mosquitoes infected via the congenital route horizontally transmitted ZIKV to suckling mice through bloodsucking. This is the first experimental evidence of offspring with vertically transmitted ZIKV initiating new horizontal transmission. The present study deepens the understanding of the vertical transmission of flaviviruses in Aedes mosquitoes and sheds light on the prevention and control of mosquito-borne diseases.
  4. Heliyon. 2020 Oct;6(10): e05181
    Daniel Reegan A, Rajiv Gandhi M, Cruz Asharaja A, Devi C, Shanthakumar SP.
      Aedes aegypti (Linn.) and Aedes albopictus (Skuse) are widespread vector mosquitoes responsible for the transmission of various disease-causing viruses to human including dengue virus (DENV). India is endemic for dengue disease and both of these vector mosquitoes are well established throughout India. Since, Aedes mosquitoes breeds in containers, WHO recommends to do a regular immature surveillance and implement appropriate control measures. Owing to the current COVID-19 pandemic, most of the countries have implemented continuous shutdown/lockdown, which affected the routine Aedes surveillance and vector control measures. In India, the first nation-wide lockdown was implemented on 24th, March 2020. As of now, Government of India has extended the lockdown till 30th, June 2020. In the present study, two rounds of Aedes surveillance was carried out in two localities of Bengaluru City (urban) of Karnataka State, India during the COVID-19 lockdown days and results were compared with pre-lockdown surveillance data to assess the impact of lockdown on Aedes larval indices, breeding habitats and dengue vector control programme. The recorded house index (HI) and Breteau index (BI) were 6.6 and 9.3 in K.P. Agrahara and 4.0 and 5.3 in Palace Guttahalli during pre-lockdown survey. The house index (HI) and Breteau index (BI) were found to be increased to 26.6 and 34.6 in K.P. Agrahara and 21.3 and 28.0 in Palace Guttahalli during the COVID-19 lockdown second survey. Aedes immature density has drastically increased in both the localities due to temporarily discontinued Aedes surveillance, larval control activities like source reduction and anti-larval measures during COVID-19 lockdown. The high indices show that the vector is increasing and this may result in higher dengue virus transmission. The results highly recommend to implement the Aedes vector control programme with limited health staffs following the physical distance and other protectives measures to prevent dengue outbreaks.
    Keywords:  Aedes surveillance; Biological sciences; COVID-19 lockdown; Ecology; Entomology; Health sciences; Insects; Larval indices; Public health; Species dominance index; Vector-borne disease
  5. Parasit Vectors. 2020 Oct 16. 13(1): 522
    Ould Lemrabott MA, Le Goff G, Kengne P, Ndiaye O, Costantini C, Mint Lekweiry K, Ould Ahmedou Salem MS, Robert V, Basco L, Simard F, Ould Mohamed Salem Boukhary A.
      BACKGROUND: Anopheles multicolor is known to be present in the arid areas of Africa north of the Sahara Desert, especially in oases. To date, its presence in Mauritania has not been reported. Here, we present the first record of its presence in Nouakchott, the capital of Mauritania. The larvae of An. multicolor, together with those of An. arabiensis, the major malaria vector in the city, were found thriving in highly saline surface water collections.METHODS: Entomological surveys were carried out during 2016-2017 in Nouakchott. Mosquito larval habitats were investigated through larval surveys while indoor resting culicid fauna were collected using hand-held aspirator. Physicochemical parameters of the larval habitats were measured on-site, at the time mosquitoes were collected. Larvae and pupae were reared to adults in the insectaries. Morphological and polymerase chain reaction (PCR)-based methods were used to identify newly emerged adults. Batches of fourth-instar larvae were used to assess salinity tolerance by exposing them to increasing concentrations of NaCl, and mortality was monitored throughout development.
    RESULTS: Morphological and molecular results confirmed that the specimens were An. multicolor and An. arabiensis. Sequences of 24 An. multicolor adult mosquitoes showed 100% nucleotide identity with the published sequences of An. multicolor from Iran. The physicochemical analysis of the water from the two larval habitats revealed highly saline conditions, with NaCl content ranging between 16.8 and 28.9 g/l (i.e. between c.50-80% seawater). Anopheles multicolor and An. arabiensis fourth-instar larvae survival rates at 17.5 g/l NaCl were 86.5% and 75%, respectively. Anopheles arabiensis larvae showed variable levels of salt tolerance according to the larval habitat. Adult An. multicolor specimens were collected resting indoor at low frequency (0.7%) compared to the other culicid mosquitoes.
    CONCLUSIONS: To the best of our knowledge, this paper is the first report of An. multicolor in Mauritania, extending the known distributional range of the species to the south, as well as to the west. Highly salt-tolerant populations of An. arabiensis and An. multicolor were observed. Because salt-water collections are widespread in Nouakchott, the relevance of these findings for the dynamics and epidemiology of malaria transmission needs to be assessed.
    Keywords:  Anopheles arabiensis; Anopheles multicolor; Larval ecology; Mauritania; Salinity
  6. PLoS One. 2020 ;15(10): e0227239
    Barrio-Nuevo KM, Cunha MS, Luchs A, Fernandes A, Rocco IM, Mucci LF, de Souza RP, Medeiros-Sousa AR, Ceretti-Junior W, Marrelli MT.
      Species of the genus Flavivirus are widespread in Brazil and are a major public health concern. The country's largest city, São Paulo, is in a highly urbanized area with a few forest fragments which are commonly used for recreation. These can be considered to present a potential risk of flavivirus transmission to humans as they are home simultaneously to vertebrate hosts and mosquitoes that are potential flavivirus vectors. The aim of this study was to conduct flavivirus surveillance in field-collected mosquitoes in the Capivari-Monos Environmental Protection Area (EPA) and identify the flavivirus species by sequence analysis in flavivirus IFA-positive pools. Monthly mosquito collections were carried out from March 2016 to April 2017 with CO2-baited CDC light traps. Specimens were identified morphologically and grouped in pools of up to 10 individuals according to their taxonomic category. A total of 260 pools of non-engorged females were inoculated into C6/36 cell culture, and the cell suspensions were analyzed by indirect immunofluorescence assay (IFA) after the incubation period. IFA-positive pools were tested by qRT-PCR with genus-specific primers targeting the flavivirus NS5 gene to confirm IFA-positive results and sequenced to identify the species. Anopheles cruzii (19.5%) and Wyeomyia confusa (15.3%) were the most frequent vector species collected. IFA was positive for flaviviruses in 2.3% (6/260) of the sample pools. This was confirmed by qRT-PCR in five pools (83.3%). All five flavivirus-positive pools were successfully sequenced and the species identified. DENV serotype 2 (DENV-2) was detected in Culex spp. and Culex vaxus pools, while ZIKV was identified in An. cruzii, Limatus durhamii and Wy. confusa pools. To the best of our knowledge, detection of flavivirus species of medical importance has never previously been reported in these species of wild-caught mosquitoes. The finding of DENV-2 and ZIKV circulating in wild mosquitoes suggests the existence of an enzootic cycle in the area. In-depth studies of DENV-2 and ZIKV, including investigation of mosquito infection, vector competence and infection in sylvatic hosts, are needed to shed light on the transmission dynamics of these important viruses and the potential risk of future outbreaks of DENV-2 and ZIKV infections in the region.
  7. Parasit Vectors. 2020 Oct 15. 13(1): 516
    Epopa PS, Millogo AA, Collins CM, North AR, Benedict MQ, Tripet F, OʼLoughlin S, Dabiré RK, Ouédraogo GA, Diabaté A.
      BACKGROUND: One of the promising current approaches to curb malaria lies in genetic vector control, the implementation of which will require an improved understanding of the movement of genetic constructs among mosquito populations. To predict potential gene flow from one area to another, it is important to begin to understand mosquito dynamics outside of the commonly-sampled village areas, and thus how genes may move between villages. This study assessed the presence and relative abundance of mosquitoes in a 6-km corridor between two villages in western Burkina Faso.METHODS: The area surrounding the villages was mapped and the road between them was used as the basis of a transect along which to sample. Five collection points were placed along this transect. To investigate both larval and adult mosquito presence, multiple sampling approaches were used surrounding each point: searching for larval sites in an area of 500 m radius, swarm sampling, human landing catches (HLC), CDC light traps and backpack aspiration catches of potential resting sites. Sampling took place twice: in September and October 2015.
    RESULTS: Adult mosquitoes from six species of Anopheles and three other genera were found along the whole transect. Anopheles gambiae (s.l.) was the most abundant followed by Anopheles nili and Anopheles coustani. Larvae of Anopheles spp. were found in small pools of surface water along the whole transect, though their presence increased with human proximity. HLC and aspiration were the most efficient methods of collecting adult mosquitoes along the whole transect, indicating that there are both host-seeking and resting mosquitoes well away from core village areas. In contrast, swarms of male mosquitoes, thought to be the principle mating locations of Anopheles spp. mosquitoes in West Africa, were only found close to the core village areas.
    CONCLUSIONS: This preliminary study indicates that Anopheles spp. mosquitoes are both present and breeding in low human-density areas along transit axes and provides both a relative evaluation of methods for use in these areas and evidence that gene flow between Sahelian population centres is likely. More robust and structured studies are nevertheless needed to come with stronger conclusions.
    Keywords:  Anopheles gambiae (s.l.); Genetic control; Human settlements; Mosquito sampling outside villages; Vector control
  8. J Trop Med. 2020 ;2020 8017187
    Msangi G, Olotu MI, Mahande AM, Philbert A, Kweka EJ.
      Background: Insecticide resistance among the vector population is the main threat to existing control tools available. The current vector control management options rely on applications of recommended public health insecticides, mainly pyrethroids through long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS). Regular monitoring of insecticide resistance does not provide information on important factors that affect parasite transmission. Such factors include vector longevity, vector competence, feeding success, and fecundity. This study investigated the impacts of insecticide resistance on longevity, feeding behaviour, and egg batch size of Anopheles gambiae s.l.Method: The larval sampling was conducted in rice fields using a standard dipper (350 ml) and reared to adults in field insectary. A WHO susceptibility test was conducted using standard treated permethrin (0.75%) and deltamethrin (0.05%) papers. The susceptible Kisumu strain was used for reference. Feeding succession and egg batch size were monitored for all survivors and control.
    Results: The results revealed that mortality rates declined by 52.5 and 59.5% for permethrin and deltamethrin, respectively. The mortality rate for the Kisumu susceptible strain was 100%. The survival rates of wild An. gambiae s.l. was between 24 and 27 days. However, the Kisumu susceptible strain blood meal feeding was significantly higher than resistant colony (t = 2.789, df = 21, P=0.011). Additionally, the susceptible An. gambiae s.s. laid more eggs than the resistant An.gambiae s.l. colony (Χ2 = 1366, df = 1, P ≤ 0.05).
    Conclusion: It can, therefore, be concluded that the wild An. gambiae s.l. had increased longevity, blood feeding, and small egg batch size compared to Kisumu susceptible colonies.
  9. J Med Entomol. 2020 Oct 12. pii: tjaa195. [Epub ahead of print]
    Medjigbodo AA, Djogbenou LS, Koumba AA, Djossou L, Badolo A, Adoha CJ, Ketoh GK, Mavoungou JF.
      An effective control of malaria vectors requires an extensive knowledge of mechanisms underlying the resistance-phenotypes developed by these vectors against insecticides. We investigated Anopheles gambiae mosquitoes from Benin and Togo for their intensity of insecticide resistance and we discussed the involvement of genotyped mechanisms in the resistance-phenotypes observed. Three- to five-day-old adult mosquitoes emerged from field and laboratory An. gambiae larvae were assayed using WHO tube intensity tests against various doses of deltamethrin: 1× (0.05%); 2× (0.1%); 5× (0.25%); 7.5× (0.375%) and those of pirimiphos-methyl: 0.5× (0.125%); 1× (0.25%). Members of An. gambiae complex were screened in field populations using polymerase chain reaction (PCR) assays. The presence of kdrR(1014F/1014S) and ace-1R(119S) mutations was also investigated using TaqMan and PCR-RFLP techniques, respectively. Anopheles gambiae from field were very resistant to deltamethrin, whereas KisKdr and AcerKdrKis strains displayed 100% mortality rates at 2× the diagnostic dose. In contrast, the field mosquitoes displayed a low resistance-intensity against 1× the diagnostic dose of pirimiphos-methyl, whereas AcerKis and AcerKdrKis strains showed susceptibility at 0.5× the diagnostic dose. Anopheles gambiae s.s., Anopheles coluzzii, and Anopheles arabiensis were identified. Allelic frequencies of kdrR (1014F) and ace-1R (119S) mutations in the field populations varied from 0.65 to 1 and 0 to 0.84, respectively. The field An. gambiae displayed high-resistance levels against deltamethrin and pirimiphos-methyl when compared with those of the laboratory An. gambiae-resistant strains. These results exhibit the complexity of underlying insecticide resistance mechanisms in these field malaria vectors.
    Keywords:   Anopheles gambiae ; deltamethrin; phenotype; pirimiphos-methyl; resistance mechanism
  10. J Pathog. 2020 ;2020 7912042
    Entonu ME, Muhammad A, Ndams IS.
      Background: Wuchereria bancrofti is the major cause of lymphatic filariasis transmitted by mosquito vectors. In the vector-parasite interaction and among other proteins, actin-1 has been implicated for successful transmission of the pathogen in laboratory-controlled experiments. However, validation of this finding from the pathogen's natural environment is required.Objective: This study is aimed at evaluating actin-1 expression upon Wuchereria bancrofti infection in mosquito vectors collected during an epidemiology study in Tsafe Local Government Area of Zamfara State, Nigeria.
    Methods: Mosquitoes were collected and identified using morphological keys, which include length of maxillary palps, pale spots on the wings, and scale patterns on the abdomen. This was followed by detection of the 188 bp SspI marker of Wuchereria bancrofti infection using polymerase chain reaction (PCR). The mRNA levels of the actin-1 gene were evaluated in the infected Anopheles gambiae sl and Culex quinquefasciatus and their controls, which were adult reared from the larvae in the study area.
    Results: The mosquitoes were identified to be Anopheles gambiae sl and Culex quinquefasciatus, while infection by Wuchereria bancrofti was confirmed by amplification of the 188 bp SspI marker. A 4.85 and 4.09 relative fold increase in actin-1 gene expression in Wuchereria bancrofti-infected Anopheles gambiae sl and Culex quinquefasciatus was observed. Thus, for the first time we reported that the actin-1 gene in wild caught mosquito vectors (Anopheles gambiae sl and Culex quinquefasciatus) infected with Wuchereria bancrofti is upregulated.
    Conclusion: The actin-1 gene is upregulated and similarly expressed during W. bancrofti infection in mosquito vectors in the study area and this may likely serve as a biomarker and viable strategy for the control of parasite transmission in endemic areas.
  11. Sci Data. 2020 Oct 13. 7(1): 342
    Atoni E, Zhao L, Hu C, Ren N, Wang X, Liang M, Mwaliko C, Yuan Z, Xia H.
      Mosquito-borne viruses such as Zika virus, Japanese Encephalitis virus and Dengue virus present an increasing global health concern. However, in-depth knowledge of the distribution and diversity of mosquito-associated viruses and their related vectors remains limited, especially for China. To promote their understanding, we present the first comprehensive dataset of the distribution and diversity of these viruses and their related vectors in China (including Taiwan, Hong Kong and Macau). Data was drawn from peer-reviewed journal articles, conference papers and thesis publications in both English and Chinese. Geographical data on mosquito-associated viruses' occurrence and related mosquito vector species was extracted, and quality-control processes employed. This dataset contains 2,428 accounts of mosquito-associated viruses' and mosquito species geo-referenced occurrences at various administrative levels in China. The prevalent mosquito-associated virus includes Japanese encephalitis virus, Dengue virus, Banna virus and Culex flavivirus, whereas the abundant mosquito vectors are Culex tritaeryohynchus, Aedes albopictus and Culex pipiens pallens. This geographical dataset delivers a distribution and diversity outline of mosquito-associated viruses in China, and also applicable in various spatial and risk-assessment analysis.
  12. Zootaxa. 2020 May 07. 4772(1): zootaxa.4772.1.2
    PĂstrav IR, DomȘa C, Mihalca AD.
      Mosquitoes (Diptera: Culicidae) are insects capable of transmitting various disease agents. They have a wide geographical range, with a higher diversity and distribution in the tropical and subtropical regions. In Romania, data on mosquito distribution are available mostly from the older literature and published in local journals; hence, it is inaccessible to the international scientific community. The aim of this review was to gather all the published data on mosquitoes in Romania by performing a comprehensive literature search, to create a publicly available georeferenced database for the distribution of mosquitoes and generate distribution maps to identify gaps in the knowledge of mosquito diversity and distribution in the country. The resultant database includes 1,509 unique records for 51 mosquito species representing seven genera: Aedes, Anopheles, Culex, Culiseta, Coquillettidia, Orthopodomyia and Uranotaenia. Knowledge of mosquito distributions is important for understanding the risks of mosquito-borne pathogens present in Romania, a country with high endemicity for various diseases, such as West Nile fever and dirofilariasis. The database also revealed important knowledge gaps, including the lack of data for the Carpathian Arch and the central part of the historical regions of Moldova and Oltenia. The gaps become more evident, as the presence and diversity of the vectors have not been studied in many areas where diseases caused by mosquito-borne pathogens are present. In conclusion, despite the numerous georeferenced records, large areas of Romania remain unexplored for the mosquito species composition, abundance and phenology. This review is a "call for action" for implementing active surveillance in the country.
    Keywords:  Diptera, distribution, mosquitoes, review, Romania
  13. Zootaxa. 2020 Oct 02. 4858(4): zootaxa.4858.4.1
    Cornel AJ, Mayi MPA, Kowo C, Foncha D, Andongma E, Anong DN, Elad M, Djomo C, Tchuinkam T, Brisco KK, Sehgal R.
      Species of Culex (Diptera: Culicidae) belonging to the subgenus Culiciomyia were collected in partially logged areas and in surrounding pristine forest (Talangaye Forest) in the Nguti Subdivision in the South-West Region of Cameroon. Mosquitoes were collected mainly by sweep netting through forest floor vegetation. Morphological species identification of African Culiciomyia relies almost exclusively on the structure of the male genitalia and the shapes of comb scales on the maxillary palpi of males. Other features of males and the habitus of females are largely indistinguishable between the species of this subgenus. In total, seven currently described species and three new species were collected in the forest. The males of the three new species are described and named as Culex apicopilosus Cornel Mayi, sp. n., Culex lanzaroi Cornel Mayi, sp. n. and Culex pseudosubaequalis Cornel Mayi, sp. n. More detailed descriptions of males of the other currently known species that were collected in the Talangaye Forest and pictorial keys to the males of all Afrotropical species of Culiciomyia, including the new species, are provided.
    Keywords:  Diptera, Culex apicopilosus, Culex lanzaroi, Culex pseudosubaequalis, taxonomy
  14. PLoS One. 2020 ;15(10): e0240207
    Hernández-Valencia JC, Rincón DS, Marín A, Naranjo-Díaz N, Correa MM.
      Landscape structure influences the distribution and abundance of anopheline mosquitoes and has an indirect impact on malaria transmission. This work aimed to determine the effect of land cover and landscape fragmentation on anopheline mosquito abundance and diversity in an important Colombian malaria endemic area, the Bajo Cauca region. Diversity indices were calculated for Anopheles mosquitoes collected in various localities of the region. Land cover types were characterized using orthorectified aerial photographs to estimate landscape metrics. The relationship between landscape fragmentation and species diversity was evaluated by regression analysis. The correlation between species abundance and land cover types was determined using canonical correspondence analyses. Results showed a statistically significant tendency for a lower diversity of the Anopheles community in landscapes with higher patch number, patch density and effective mesh size. For most species, there was evidence of a significant relationship between species abundance and land covers modified by anthropic activities which generate forest loss. These results indicate that activities that modify the landscape structure and land cover composition generate changes that affect the spatial distribution and composition of epidemiologically-important Anopheles species, which may impact malaria distribution in a region. This information is useful to guide control interventions that promote unfavorable landscapes for malaria vector propagation.
  15. Braz J Biol. 2020 Oct 12. pii: S1519-69842020005032204. [Epub ahead of print]
    Vieira-Neta MRA, Soares-da-Silva J, Viana JL, Silva MC, Tadei WP, Pinheiro VCS.
      Bacillus thuringiensis is the most commonly used entomopathogen in the control of Aedes aegypti, which is a vector for different etiological agents that cause serious infections in humans. Several studies aim to isolate strains of this bacterium from different environments, with the perspective of selecting isolates with larvicidal activity for mosquitoes. Aiming at the insecticidal action of B. thuringiensis, the present study aimed to prospect B. thuringiensis of restinga and mangrove soils from the state of Maranhão, Brazil, with toxic potential for use in the biological control of Ae. aegypti. Bioassays were performed to determine the entomopathogenic activity of the bacilli against Ae. aegypti and lethal concentrations (LC50 and CL90) were estimated after the tests. Polymerase Chain Reaction and SDS-PAGE techniques were performed to verify the gene and protein content of the isolates, respectively. The soil of the mangrove and restinga ecosystems showed potential for obtaining B. thuringiensis. This isolate, in addition to having proteins with molecular mass similar to the toxins Cry and Cyt, also presented several diptera-specific genes cry and cyt, demonstrating that it has high potential to be used in the biological control of Ae. aegypti.
  16. Sci Rep. 2020 Oct 14. 10(1): 17201
    Olademehin OP, Liu C, Rimal B, Adegboyega NF, Chen F, Sim C, Kim SJ.
      Culex pipiens is a major carrier of the West Nile Virus, the leading cause of mosquito-borne disease in the continental United States. Cx. pipiens survive overwinter through diapause which is an important survival strategy that is under the control of insulin signaling and Foxo by regulating energy metabolism. Three homologous candidate genes, glycogen synthase (glys), atp-binding cassette transporter (atp), and low-density lipoprotein receptor chaperone (ldlr), that are under the regulation of Foxo transcription factor were identified in Cx. pipiens. To validate the gene functions, each candidate gene was silenced by injecting the target dsi-RNA to female Cx. pipiens during the early phase of diapause. The dsi-RNA injected diapause-destined female post-adult eclosion were fed for 7 days with 10% glucose containing 1% D-[13C6]glucose. The effects of dsi-RNA knockdown on glucose metabolism in intact mosquitoes were monitored using 13C solid-state NMR and ATR-FTIR. Our finding shows that the dsi-RNA knockdown of all three candidate genes suppressed glycogen and lipid biosyntheses resulting in inhibition of long-term carbon energy storage in diapausing females.
  17. Neuron. 2020 Oct 08. pii: S0896-6273(20)30719-4. [Epub ahead of print]
    Jové V, Gong Z, Hol FJH, Zhao Z, Sorrells TR, Carroll TS, Prakash M, McBride CS, Vosshall LB.
      Blood-feeding mosquitoes survive by feeding on nectar for metabolic energy but require a blood meal to develop eggs. Aedes aegypti females must accurately discriminate blood and nectar because each meal promotes mutually exclusive feeding programs with distinct sensory appendages, meal sizes, digestive tract targets, and metabolic fates. We investigated the syringe-like blood-feeding appendage, the stylet, and discovered that sexually dimorphic stylet neurons taste blood. Using pan-neuronal calcium imaging, we found that blood is detected by four functionally distinct stylet neuron classes, each tuned to specific blood components associated with diverse taste qualities. Stylet neurons are insensitive to nectar-specific sugars and respond to glucose only in the presence of additional blood components. The distinction between blood and nectar is therefore encoded in specialized neurons at the very first level of sensory detection in mosquitoes. This innate ability to recognize blood is the basis of vector-borne disease transmission to millions of people worldwide.
    Keywords:  Aedes aegypti; GCaMP calcium imaging; blood-feeding behavior; chemogenetics; gustatory receptors; ionotropic receptors; mosquito; nectar-feeding behavior; stylet; taste
  18. Malar J. 2020 Oct 16. 19(1): 371
    Yaro JB, Ouedraogo A, Ouedraogo ZA, Diarra A, Lankouande M, Agboraw E, Worrall E, Toe KH, Sanou A, Guelbeogo WM, Sagnon N, Ranson H, Tiono AB, Lindsay SW, Wilson AL.
      BACKGROUND: Progress in controlling malaria has stalled in recent years. Today the malaria burden is increasingly concentrated in a few countries, including Burkina Faso, where malaria is not declining. A cohort study was conducted to identify risk factors for malaria infection in children in southwest Burkina Faso, an area with high insecticide-treated net (ITN) coverage and insecticide-resistant vectors.METHODS: Incidence of Plasmodium falciparum infection was measured in 252 children aged 5 to 15 years, using active and passive detection, during the 2017 transmission season, following clearance of infection. Demographic, socio-economic, environmental, and entomological risk factors, including use of ITNs and insecticide resistance were monitored.
    RESULTS: During the six-month follow-up period, the overall incidence of P. falciparum infection was 2.78 episodes per child (95% CI = 2.66-2.91) by microscopy, and 3.11 (95% CI = 2.95-3.28) by polymerase chain reaction (PCR). The entomological inoculation rate (EIR) was 80.4 infective bites per child over the six-month malaria transmission season. At baseline, 80.6% of children were reported as sleeping under an ITN the previous night, although at the last survey, 23.3% of nets were in poor condition and considered no longer protective. No association was found between the rate of P. falciparum infection and either EIR (incidence rate ratio (IRR): 1.00, 95% CI: 1.00-1.00, p = 0.08) or mortality in WHO tube tests when vectors were exposed to 0.05% deltamethrin (IRR: 1.05, 95% CI: 0.73-1.50, p = 0.79). Travel history (IRR: 1.52, 95% CI: 1.45-1.59, p < 0.001) and higher socio-economic status were associated with an increased risk of P. falciparum infection (IRR: 1.05, 95% CI: 1.00-1.11, p = 0.04).
    CONCLUSIONS: Incidence of P. falciparum infection remains overwhelmingly high in the study area. The study findings suggest that because of the exceptionally high levels of malaria transmission in the study area, malaria elimination cannot be achieved solely by mass deployment of ITNs and additional control measures are needed.
    Keywords:  Burkina faso; Cohort study; Epidemiology; Insecticide resistance; Malaria; Vector control
  19. Insects. 2020 Oct 13. pii: E693. [Epub ahead of print]11(10):
    Lukindu M, Love RR, Guelbeogo MW, Small ST, Stephens MT, Campbell NR, Sagnon N, Costantini C, Besansky NJ.
      Polymorphic chromosomal inversions have been implicated in local adaptation. In anopheline mosquitoes, inversions also contribute to epidemiologically relevant phenotypes such as resting behavior. Progress in understanding these phenotypes and their mechanistic basis has been hindered because the only available method for inversion genotyping relies on traditional cytogenetic karyotyping, a rate-limiting and technically difficult approach that is possible only for the fraction of the adult female population at the correct gonotrophic stage. Here, we focus on an understudied malaria vector of major importance in sub-Saharan Africa, Anopheles funestus. We ascertain and validate tag single nucleotide polymorphisms (SNPs) using high throughput molecular assays that allow rapid inversion genotyping of the three most common An. funestus inversions at scale, overcoming the cytogenetic karyotyping barrier. These same inversions are the only available markers for distinguishing two An. funestus ecotypes that differ in indoor resting behavior, Folonzo and Kiribina. Our new inversion genotyping tools will facilitate studies of ecotypic differentiation in An. funestus and provide a means to improve our understanding of the roles of Folonzo and Kiribina in malaria transmission.
    Keywords:  Anopheles funestus; chromosomal inversion polymorphism; inversion genotyping; karyotyping; malaria vector; polytene chromosome analysis; tag SNP
  20. Cochrane Database Syst Rev. 2020 Oct 15. 10 CD013398
    Furnival-Adams J, Olanga EA, Napier M, Garner P.
      BACKGROUND: Despite being preventable, malaria remains an important public health problem. The World Health Organization (WHO) reports that overall progress in malaria control has plateaued for the first time since the turn of the century. Researchers and policymakers are therefore exploring alternative and supplementary malaria vector control tools. Research in 1900 indicated that modification of houses may be effective in reducing malaria: this is now being revisited, with new research now examining blocking house mosquito entry points or modifying house construction materials to reduce exposure of inhabitants to infectious bites.OBJECTIVES: To assess the effects of house modifications on malaria disease and transmission.
    SEARCH METHODS: We searched the Cochrane Infectious Diseases Group Specialized Register; Central Register of Controlled Trials (CENTRAL), published in the Cochrane Library; MEDLINE (PubMed); Embase (OVID); Centre for Agriculture and Bioscience International (CAB) Abstracts (Web of Science); and the Latin American and Caribbean Health Science Information database (LILACS), up to 1 November 2019. We also searched the WHO International Clinical Trials Registry Platform (, (, and the ISRCTN registry ( to identify ongoing trials up to the same date.
    SELECTION CRITERIA: Randomized controlled trials, including cluster-randomized controlled trials (cRCTs), cross-over studies, and stepped-wedge designs were eligible, as were quasi-experimental trials, including controlled before-and-after studies, controlled interrupted time series, and non-randomized cross-over studies. We only considered studies reporting epidemiological outcomes (malaria case incidence, malaria infection incidence or parasite prevalence). We also summarised qualitative studies conducted alongside included studies.
    DATA COLLECTION AND ANALYSIS: Two review authors selected eligible studies, extracted data, and assessed the risk of bias. We used risk ratios (RR) to compare the effect of the intervention with the control for dichotomous data. For continuous data, we presented the mean difference; and for count and rate data, we used rate ratios. We presented all results with 95% confidence intervals (CIs). We assessed the certainty of evidence using the GRADE approach.
    MAIN RESULTS: Six cRCTs met our inclusion criteria, all conducted in sub-Saharan Africa; three randomized by household, two by village, and one at the community level. All trials assessed screening of windows, doors, eaves, ceilings or any combination of these; this was either alone, or in combination with eave closure, roof modification or eave tube installation (a "lure and kill" device that reduces mosquito entry whilst maintaining some airflow). In two trials, the interventions were insecticide-based. In five trials, the researchers implemented the interventions. The community implemented the interventions in the sixth trial. At the time of writing the review, two of the six trials had published results, both of which compared screened houses (without insecticide) to unscreened houses. One trial in Ethiopia assessed screening of windows and doors. Another trial in the Gambia assessed full screening (screening of eaves, doors and windows), as well as screening of ceilings only. Screening may reduce clinical malaria incidence caused by Plasmodium falciparum (rate ratio 0.38, 95% CI 0.18 to 0.82; 1 trial, 184 participants, 219.3 person-years; low-certainty evidence; Ethiopian study). For malaria parasite prevalence, the point estimate, derived from The Gambia study, was smaller (RR 0.84, 95% CI 0.60 to 1.17; 713 participants, 1 trial; moderate-certainty evidence), and showed an effect on anaemia (RR 0.61, 95% CI 0.42, 0.89; 705 participants; 1 trial, moderate-certainty evidence). Screening may reduce the entomological inoculation rate (EIR): both trials showed lower estimates in the intervention arm. In the Gambian trial, there was a mean difference in EIR between the control houses and treatment houses ranging from 0.45 to 1.50 (CIs ranged from -0.46 to 2.41; low-certainty evidence), depending on the study year and treatment arm. The Ethiopian trial reported a mean difference in EIR of 4.57, favouring screening (95% CI 3.81 to 5.33; low-certainty evidence). Pooled analysis of the trials showed that individuals living in fully screened houses were slightly less likely to sleep under a bed net (RR 0.84, 95% CI 0.65 to 1.09; 2 trials, 203 participants). In one trial, bed net usage was also lower in individuals living in houses with screened ceilings (RR 0.69, 95% CI 0.50 to 0.95; 1 trial, 135 participants).
    AUTHORS' CONCLUSIONS: Based on the two trials published to date, there is some evidence that screening may reduce malaria transmission and malaria infection in people living in the house. The four trials awaiting publication are likely to enrich the current evidence base, and we will add these to this review when they become available.