bims-mosdis Biomed News
on Mosquito distribution and disease
Issue of 2020‒02‒23
seventeen papers selected by
Richard Halfpenny
Staffordshire University

  1. Parasit Vectors. 2020 Feb 17. 13(1): 78
    Sippy R, Rivera GE, Sanchez V, Heras F, Morejón B, Beltrán E, Hikida RS, López-Latorre MA, Aguirre A, Stewart-Ibarra AM, Larsen DA, Neira M.
      BACKGROUND: Illnesses transmitted by Aedes aegypti (Linnaeus, 1762) such as dengue, chikungunya and Zika comprise a considerable global burden; mosquito control is the primary public health tool to reduce disease transmission. Current interventions are inadequate and insecticide resistance threatens the effectiveness of these options. Dried attractive bait stations (DABS) are a novel mechanism to deliver insecticide to Ae. aegypti. The DABS are a high-contrast 28 inch2 surface coated with dried sugar-boric acid solution. Aedes aegypti are attracted to DABS by visual cues only, and the dried sugar solution elicits an ingestion response from Ae. aegypti landing on the surface. The study presents the development of the DABS and tests of their impact on Ae. aegypti mortality in the laboratory and a series of semi-field trials.METHODS: We conducted multiple series of laboratory and semi-field trials to assess the survivability of Ae. aegypti mosquitoes exposed to the DABS. In the laboratory experiments, we assessed the lethality, the killing mechanism, and the shelf life of the device through controlled experiments. In the semi-field trials, we released laboratory-reared female Ae. aegypti into experimental houses typical of peri-urban tropical communities in South America in three trial series with six replicates each. Laboratory experiments were conducted in Quito, Ecuador, and semi-field experiments were conducted in Machala, Ecuador, an area with abundant wild populations of Ae. aegypti and endemic arboviral transmission.
    RESULTS: In the laboratory, complete lethality was observed after 48 hours regardless of physiological status of the mosquito. The killing mechanism was determined to be through ingestion, as the boric acid disrupted the gut of the mosquito. In experimental houses, total mosquito mortality was greater in the treatment house for all series of experiments (P < 0.0001).
    CONCLUSIONS: The DABS devices were effective at killing female Ae. aegypti under a variety of laboratory and semi-field conditions. DABS are a promising intervention for interdomiciliary control of Ae. aegypti and arboviral disease prevention.
    Keywords:  ATSB; Aedes aegypti; Arbovirus; Attractive bait; Dengue; Semi-field; Toxic sugar bait; Vector control
  2. Int J Environ Res Public Health. 2020 Feb 17. pii: E1291. [Epub ahead of print]17(4):
    Leal SDV, Fernandes Varela IB, Lopes Gonçalves AAL, Sousa Monteiro DD, Ramos de Sousa CM, Lima Mendonça MDL, De Pina AJ, Alves MJ, Osório HC.
      BACKGROUND: Mosquito-borne viruses, such as Zika, dengue, yellow fever, and chikungunya, are important causes of human diseases nearly worldwide. The greatest health risk for arboviral disease outbreaks is the presence of the most competent and highly invasive domestic mosquito, Aedes aegypti. In Cabo Verde, two recent arbovirus outbreaks were reported, a dengue outbreak in 2009, followed by a Zika outbreak in 2015. This study is the first entomological survey for Ae. aegypti that includes all islands of Cabo Verde archipelago, in which we aim to evaluate the actual risk of vector-borne arboviruses as a continuous update of the geographical distribution of this species.METHODS: In order to assess its current distribution and abundance, we undertook a mosquito larval survey in the nine inhabited islands of Cabo Verde from November 2018 to May 2019. Entomological larval survey indices were calculated, and the abundance analyzed. We collected and identified 4045 Ae. aegypti mosquitoes from 264 positive breeding sites in 22 municipalities and confirmed the presence of Ae. aegypti in every inhabited island. Results: Water drums were found to be the most prevalent containers (n = 3843; 62.9%), but puddles (n = 27; 0.4%) were the most productive habitats found. The overall average of the House, Container, and Breteau larval indices were 8.4%, 4.4%, and 10.9, respectively. However, 15 out of the 22 municipalities showed that the Breteau Index was above the epidemic risk threshold.
    CONCLUSION: These results suggest that if no vector control measures are considered to be in place, the risk of new arboviral outbreaks in Cabo Verde is high. The vector control strategy adopted must include measures of public health directed to domestic water storage and management.
    Keywords:  Aedes aegypti; Cabo Verde; arboviruses; control; larval index; surveillance
  3. Parasit Vectors. 2020 Feb 19. 13(1): 91
    Dallimore T, Goodson D, Batke S, Strode C.
      BACKGROUND: The international movement of used tyres is a major factor responsible for global introductions of Aedes invasive mosquitoes (AIMs) (Diptera: Culicidae) that are major disease vectors (e.g. dengue, Zika, chikungunya and yellow fever). Surveillance methods are restricted by expense, availability and efficiency to detect all life stages. Currently, no tested method exists to screen imported used tyres for eggs in diapause, the life stage most at risk from accidental introduction. Here we test the efficiency of adhesive tape as an affordable and readily available material to screen tyres for eggs, testing its effect on hatch rate, larval development, DNA amplification and structural damage on the egg surface.RESULTS: We demonstrated that the properties of adhesive tape can influence pick up of dormant eggs attached to dry surfaces. Tapes with high levels of adhesion, such as duct tape, removed eggs with high levels of efficiency (97% ± 3.14). Egg numbers collected from cleaned used tyres were found to explain larval hatch rate success well, particularly in subsequent larval to adult emergence experiments. The strength of this relationship decreased when we tested dirty tyres. Damage to the exochorion was observed following scanning electron microscopy (SEM), possibly resulting in the high variance in the observed model. We found that five days was the optimal time for eggs to remain on all tested tapes for maximum return on hatch rate success. Tape type did not inhibit amplification of DNA of eggs from three, five or ten days of exposure. Using this DNA, genotyping of AIMs was possible using species-specific markers.
    CONCLUSIONS: We demonstrated for the first time that adhesive tapes are effective at removing AIM eggs from tyres. We propose that this method could be a standardised tool for surveillance to provide public health authorities and researchers with an additional method to screen tyre cargo. We provide a screening protocol for this purpose. This method has a global applicability and in turn can lead to increased predictability of introductions and improve screening methods at high risk entry points.
    Keywords:  AIMs; Aedes aegypti; Aedes albopictus; Dengue; Eggs; Mosquito; Surveillance; Tyres; Zika
  4. Parasit Vectors. 2020 Feb 17. 13(1): 80
    Wooding M, Naudé Y, Rohwer E, Bouwer M.
      The use of semiochemicals in odour-based traps for surveillance and control of vector mosquitoes is deemed a new and viable component for integrated vector management programmes. Over 114 semiochemicals have been identified, yet implementation of these for management of infectious diseases such as malaria, dengue, chikungunya and Rift Valley fever is still a major challenge. The difficulties arise due to variation in how different mosquito species respond to not only single chemical compounds but also complex chemical blends. Additionally, mosquitoes respond to different volatile blends when they are looking for a mating partner, oviposition sites or a meal. Analytically the challenge lies not only in correctly identifying these semiochemical signals and cues but also in developing formulations that effectively mimic blend ratios that different mosquito species respond to. Only then can the formulations be used to enhance the selectivity and efficacy of odour-based traps. Understanding how mosquitoes use semiochemical cues and signals to survive may be key to unravelling these complex interactions. An overview of the current studies of these chemical messages and the chemical ecology involved in complex behavioural patterns is given. This includes an updated list of the semiochemicals which can be used for integrated vector control management programmes. A thorough understanding of these semiochemical cues is of importance for the development of new vector control methods that can be integrated into established control strategies.
    Keywords:  Aedes; Anopheles; Chemical communication; Culex; Malaria; Mosquito life-cycle; Semiochemicals; Vector mosquitoes
  5. Acta Trop. 2020 Feb 14. pii: S0001-706X(20)30086-3. [Epub ahead of print] 105398
    Lorenz C, Chiaravalloti-Neto F, de Oliveira Lage M, Quintanilha JA, Parra MC, Dibo MR, Fávaro EA, Guirado MM, Nogueira ML.
      Mosquito-borne diseases affect millions of individuals worldwide; the area of endemic transmission has been increasing due to several factors linked to globalization, urban sprawl, and climate change. The Aedes aegypti mosquito plays a central role in the dissemination of dengue, Zika, chikungunya, and urban yellow fever. Current preventive measures include mosquito control programs; however, identifying high-risk areas for mosquito infestation over a large geographic region based only on field surveys is labor-intensive and time-consuming. Thus, the objective of this study was to assess the potential of remote satellite images (WorldView) for determining land features associated with Ae. aegypti adult infestations in São José do Rio Preto/SP, Brazil. We used data from 60 adult mosquito traps distributed along four summers; the remote sensing images were classified by land cover types using a supervised classification method. We modeled the number of Ae. aegypti using a Poisson probability distribution with a geostatistical approach. The models were constructed in a Bayesian context using the Integrated nested Laplace Approximations and Stochastic Partial Differential Equation method. We showed that an infestation of Ae. aegypti adult mosquitoes was positively associated with the presence of asbestos roofing and roof slabs. This may be related to several other factors, such as socioeconomic or environmental factors. The usage of asbestos roofing may be more prevalent in socioeconomically poor areas, while roof slabs may retain rainwater and contribute to the generation of temporary mosquito breeding sites. Although preliminary, our results demonstrate the utility of satellite remote sensing in identifying landscape differences in urban environments using a geostatistical approach, and indicated directions for future research. Further analyses including other variables, such as land surface temperature, may reveal more complex relationships between urban mosquito micro-habitats and land cover features.
    Keywords:  Bayesian approach; Geostatistical analysis; Landscape; Mosquito control
  6. Acta Trop. 2020 Feb 15. pii: S0001-706X(19)30884-8. [Epub ahead of print] 105394
    Medeiros-Sousa AR, de Oliveira-Christe R, Camargo AA, Scinachi CA, Milani GM, Urbinatti PR, Natal D, Ceretti-Junior W, Marrelli MT.
      Water's physical and chemical characteristics are important constraints in aquatic ecosystems, acting on the development, survival, and adaptation of different organisms. Immature forms of mosquitoes develop in widely diverse aquatic environments and are mainly found in permanent or temporary freshwater bodies with little or no movement. The current study aimed to investigate whether variations in larval habitats' pH, salinity, dissolved oxygen, and water temperature influence the composition of Culicidae assemblages and the presence and abundance of Aedes albopictus and Ae. aegypti. From August 2012 to July 2013, captures of immature forms and measurement of water's physical and chemical profiles were performed monthly in natural and artificial breeding sites in four urban parks in the city of São Paulo, Brazil. Changes in species composition related to the parameters' variation were assessed by multivariate analysis. Regression trees were performed to evaluate the effect of breeding sites' physical and chemical variations on the presence and abundance of Ae. albopictus and Ae. aegypti. The observations suggest ranges of conditions for the measured variables in which most species tend to be found more frequently, and pH and salinity are the variables most closely associated with variations in mosquito composition. Ae. aegypti and Ae. albopictus were present in both natural and artificial breeding sites and were observed under significantly varying conditions of pH, salinity, dissolved oxygen, and temperature. For Ae. albopictus, larval habitat type and pH were the best predictors of incidence and abundance. For Ae. aegypti, pH and salinity were the best predictors of abundance, while dissolved oxygen and larval habitat type were better predictors of presence. This information broadens our understanding of the ecology and interaction of the investigated species with abiotic factors in the aquatic environments, providing useful data for studies that seek to elucidate the underlying mechanisms of selection and colonization of breeding sites by these mosquitoes. This study also reinforces previous observations indicating that Ae. albopictus and Ae. aegypti can colonize diverse types of larval habitats with widely varying physical and chemical conditions.
    Keywords:  Aedes aegypti; Aedes albopictus; Breeding sites, Physical and chemical parameters; Mosquitoes
  7. Parasit Vectors. 2020 Feb 18. 13(1): 87
    Kaddumukasa MA, Wright J, Muleba M, Stevenson JC, Norris DE, Coetzee M.
      BACKGROUND: Anopheles funestus (s.s.) is a primary vector of the malaria parasite Plasmodium falciparum in Africa, a human pathogen that causes almost half a million deaths each year. The population structure of An. funestus was examined in samples from Uganda and the southern African countries of Malawi, Mozambique, Zambia and Zimbabwe.METHODS: Twelve microsatellites were used to estimate the genetic diversity and differentiation of An. funestus from 13 representative locations across five countries. These were comprised of four sites from Uganda, three from Malawi and two each from Mozambique, Zambia and Zimbabwe.
    RESULTS: All loci were highly polymorphic across the populations with high allelic richness and heterozygosity. A high genetic diversity was observed with 2-19 alleles per locus and an average number of seven alleles. Overall, expected heterozygosity (He) ranged from 0.65 to 0.79. When samples were pooled three of the 12 microsatellite loci showed Hardy-Weinberg equilibrium. Unsupervised Bayesian clustering analysis of microsatellite data revealed two clusters with An. funestus samples from Mozambique, Uganda and Zambia falling into one group and Malawi and Zimbabwe into another. The overall genetic differentiation between the populations was moderate (FST = 0.116). Pairwise differentiation between the pairs was low but significant. A weak but significant correlation was established between genetic and geographical distance for most populations.
    CONCLUSIONS: High genetic diversity revealed by the loci with low to moderate differentiation, identified two clusters among the An. funestus populations. Further research on the population dynamics of An. funestus in east and southern Africa is essential to understand the implications of this structuring and what effect it may have on the efficient implementation of mosquito vector control strategies.
    Keywords:  Anopheles funestus; East Africa; Malaria; Microsatellites; Population differentiation; Southern Africa
  8. Med Vet Entomol. 2020 Feb 20.
    Rowbottom R, Carver S, Barmuta LA, Weinstein P, Allen GR.
      Saltmarsh breeding mosquitoes are an important source of vectors for arboviral transmission. In southern Australia, the most prominent vector borne disease, Ross River virus (Togaviridae: Alphavirus) (RRV), is transmitted by the saltmarsh mosquito (Diptera: Culicidae) Aedes camptorhynchus (Thomson). However, the factors driving the abundance of this mosquito within and among saltmarshes are poorly understood. To predict the abundance of this mosquito within saltmarshes, the environmental conditions and aquatic invertebrate ecology of three temperate saltmarshes habitats were monitored over two seasons. Up to 44% of first-instar mosquito numbers and 21% of pupal numbers were accounted for by environmental variables. Samphire vegetation cover was a common predictor of first-instar numbers across sites although, between saltmarshes, aquatic factors such as high salinity, temperatures less than 22 °C and water body volume were important predictors. The identified predictors of pupal numbers were more variable and included high tides, waterbody volume and alkalinity. The composition of invertebrate functional feeding groups differed between saltmarshes and showed that an increased diversity led to fewer mosquitoes. It was evident that apparently similar saltmarshes can vary markedly in invertebrate assemblages, water availability and conditions through tidal inundations, rainfall or waterbody permanency. The present study advances insight into predictors of vector mosquito numbers that drive the risk of RRV outbreaks.
    Keywords:  Aedes camptorhynchus; RRV; Tasmania; functional feeding groups; habitat comparison; seasonal variability
  9. Ecol Evol. 2020 Feb;10(3): 1581-1591
    Ross PA, Callahan AG, Yang Q, Jasper M, Arif MAK, Afizah AN, Nazni WA, Hoffmann AA.
      Wolbachia are maternally inherited endosymbiotic bacteria found within many insect species. Aedes mosquitoes experimentally infected with Wolbachia are being released into the field for Aedes-borne disease control. These Wolbachia infections induce cytoplasmic incompatibility which is used to suppress populations through incompatible matings or replace populations through the reproductive advantage provided by this mechanism. However, the presence of naturally occurring Wolbachia in target populations could interfere with both population replacement and suppression programs depending on the compatibility patterns between strains. Aedes aegypti were thought to not harbor Wolbachia naturally but several recent studies have detected Wolbachia in natural populations of this mosquito. We therefore review the evidence for natural Wolbachia infections in A. aegypti to date and discuss limitations of these studies. We draw on research from other mosquito species to outline the potential implications of natural Wolbachia infections in A. aegypti for disease control. To validate previous reports, we obtained a laboratory population of A. aegypti from New Mexico, USA, that harbors a natural Wolbachia infection, and we conducted field surveys in Kuala Lumpur, Malaysia, where a natural Wolbachia infection has also been reported. However, we were unable to detect Wolbachia in both the laboratory and field populations. Because the presence of naturally occurring Wolbachia in A. aegypti could have profound implications for Wolbachia-based disease control programs, it is important to continue to accurately assess the Wolbachia status of target Aedes populations.
    Keywords:  Aedes aegypti; Wolbachia; cytoplasmic incompatibility; dengue
  10. Expert Rev Vaccines. 2020 Feb 20.
    Thompson R, Martin Del Campo J, Constenla D.
      INTRODUCTION: Aedes-borne arboviruses imposes significant economic and public health costs inAreas covered: We performed a systematic review of the economic evidence surrounding aedes-borne arboviruses and strategies to prevent and control these diseases to inform disease control policy decisions and research directions. We searched four databases covering an 18-year period (2000-2018) to identify arboviral disease-related cost of illness studies, cost studies of vector control and prevention strategies, cost-effectiveness analyses and cost-benefit analyses. We identified 74 published studies that revealed substantial global total costs in yellow fever virus and dengue virus ranging from $2.1 billion - 57.3 billion. Cost studies of vector control and surveillance programs are limited, but a few studies found that costs of vector control programs ranged from $5.62to $73.5 million. Cost-effectiveness evidence was limited across Aedes-borne diseases, but generally found targeted dengue vaccination programs cost-effective. This review revealed insufficient economic evidence for vaccine introduction and implementation of surveillance and vector control programs.Expert opinion: Evidence of the economic burden of aedes-borne arboviruses and the economic impact of strategies for arboviral disease prevention and control is critical to inform policy decisions and to secure continued financial support for these preventive and control measures.
    Keywords:  Aedes-borne arboviruses; Economics; Zika virus; chikungunya virus; control; cost-benefit; cost-effectiveness; costing; delivery costs; dengue fever; prevention; surveillance; vaccines; yellow fever
  11. Front Vet Sci. 2020 ;7 15
    Auerswald H, Ruget AS, Ladreyt H, In S, Mao S, Sorn S, Tum S, Duong V, Dussart P, Cappelle J, Chevalier V.
      Mosquito-borne flaviviruses with an enzootic transmission cycle like Japanese encephalitis virus (JEV) and West Nile virus (WNV) are a major public health concern. The circulation of JEV in Southeast Asia is well-documented, and the important role of pigs as amplification hosts for the virus is long known. The influence of other domestic animals especially poultry that lives in high abundance and close proximity to humans is not intensively analyzed. Another understudied field in Asia is the presence of the closely related WNV. Such analyses are difficult to perform due to the intense antigenic cross-reactivity between these viruses and the lack of suitable standardized serological assays. The main objective of this study was to assess the prevalence of JEV and WNV flaviviruses in domestic birds, detailed in chickens and ducks, in three different Cambodian provinces. We determined the flavivirus seroprevalence using an hemagglutination inhibition assay (HIA). Additionally, we investigated in positive samples the presence of JEV and WNV neutralizing antibodies (nAb) using foci reduction neutralization test (FRNT). We found 29% (180/620) of the investigated birds positive for flavivirus antibodies with an age-depended increase of the seroprevalence (OR = 1.04) and a higher prevalence in ducks compared to chicken (OR = 3.01). Within the flavivirus-positive birds, we found 43% (28/65) with nAb against JEV. We also observed the expected cross-reactivity between JEV and WNV, by identifying 18.5% double-positive birds that had higher titers of nAb than single-positive birds. Additionally, seven domestic birds (10.7%) showed only nAb against WNV and no nAb against JEV. Our study provides evidence for an intense JEV circulation in domestic birds in Cambodia, and the first serological evidence for WNV presence in Southeast Asia since decades. These findings mark the need for a re-definition of areas at risk for JEV and WNV transmission, and the need for further and intensified surveillance of mosquito-transmitted diseases in domestic animals.
    Keywords:  Cambodia; Japanese encephalitis virus; West Nile virus; domestic birds; poultry; serology
  12. Cell Rep. 2020 Feb 12. pii: S2211-1247(20)30119-4. [Epub ahead of print]
    Giovanetti M, Faria NR, Lourenço J, Goes de Jesus J, Xavier J, Claro IM, Kraemer MUG, Fonseca V, Dellicour S, Thézé J, da Silva Salles F, Gräf T, Silveira PP, do Nascimento VA, Costa de Souza V, de Melo Iani FC, Castilho-Martins EA, Cruz LN, Wallau G, Fabri A, Levy F, Quick J, de Azevedo V, Aguiar RS, de Oliveira T, Bôtto de Menezes C, da Costa Castilho M, Terra TM, Souza da Silva M, Bispo de Filippis AM, Luiz de Abreu A, Oliveira WK, Croda J, Campelo de Albuquerque CF, Nunes MRT, Sabino EC, Loman N, Naveca FG, Pybus OG, Alcantara LC.
      Zika virus (ZIKV) has caused an explosive epidemic linked to severe clinical outcomes in the Americas. As of June 2018, 4,929 ZIKV suspected infections and 46 congenital syndrome cases had been reported in Manaus, Amazonas, Brazil. Although Manaus is a key demographic hub in the Amazon region, little is known about the ZIKV epidemic there, in terms of both transmission and viral genetic diversity. Using portable virus genome sequencing, we generated 59 ZIKV genomes in Manaus. Phylogenetic analyses indicated multiple introductions of ZIKV from northeastern Brazil to Manaus. Spatial genomic analysis of virus movement among six areas in Manaus suggested that populous northern neighborhoods acted as sources of virus transmission to other neighborhoods. Our study revealed how the ZIKV epidemic was ignited and maintained within the largest urban metropolis in the Amazon. These results might contribute to improving the public health response to outbreaks in Brazil.
  13. Sci Adv. 2020 Feb;6(6): eaax7989
    Qiu Y, Xu YP, Wang M, Miao M, Zhou H, Xu J, Kong J, Zheng D, Li RT, Zhang RR, Guo Y, Li XF, Cui J, Qin CF, Zhou X.
      Mosquito-borne flaviviruses infect both mammals and mosquitoes. RNA interference (RNAi) has been demonstrated as an anti-flavivirus mechanism in mosquitoes; however, whether and how flaviviruses induce and antagonize RNAi-mediated antiviral immunity in mammals remains unknown. We show that the nonstructural protein NS2A of dengue virus-2 (DENV2) act as a viral suppressor of RNAi (VSR). When NS2A-mediated RNAi suppression was disabled, the resulting mutant DENV2 induced Dicer-dependent production of abundant DENV2-derived siRNAs in differentiated mammalian cells. VSR-disabled DENV2 showed severe replication defects in mosquito and mammalian cells and in mice that were rescued by RNAi deficiency. Moreover, NS2As of multiple flaviviruses act as VSRs in vitro and during viral infection in both organisms. Overall, our findings demonstrate that antiviral RNAi can be induced by flavivirus, while flavivirus uses NS2A as a bona fide VSR to evade RNAi in mammals and mosquitoes, highlighting the importance of RNAi in flaviviral vector-host life cycles.
  14. Sci Adv. 2020 Jan;6(5): eaaw7449
    Carey JM, Chi V, Flynn DJ, Nyhan B, Zeitzoff T.
      Disease epidemics and outbreaks often generate conspiracy theories and misperceptions that mislead people about the risks they face and how best to protect themselves. We investigate the effectiveness of interventions aimed at combating false and unsupported information about the Zika epidemic and subsequent yellow fever outbreak in Brazil. Results from a nationally representative survey show that conspiracy theories and other misperceptions about Zika are widely believed. Moreover, results from three preregistered survey experiments suggest that efforts to counter misperceptions about diseases during epidemics and outbreaks may not always be effective. We find that corrective information not only fails to reduce targeted Zika misperceptions but also reduces the accuracy of other beliefs about the disease. In addition, although corrective information about the better-known threat from yellow fever was more effective, none of these corrections affected support for vector control policies or intentions to engage in preventive behavior.
  15. J Gen Virol. 2020 Feb 18.
    Caldwell HS, Ngo K, Pata JD, Kramer LD, Ciota AT.
      The fidelity of flaviviruses is thought to be tightly regulated for optimal fitness within and between hosts. West Nile virus (WNV) high-fidelity (HiFi) mutations V793I and G806R within the RNA-dependent RNA polymerase, and low-fidelity (LoFi) mutation T248I within the methyltransferase, were previously shown to attenuate infectivity and replicative fitness in Culex mosquitoes and Culex tarsalis (CXT) cells but not in mammalian cells. We hypothesized that fidelity alterations would modify adaptation and maintenance in a host-specific manner. To test this hypothesis, wild-type (WT), HiFi (V793I/G806R) and LoFi (T248I) variants were sequentially passaged eight times in avian (PDE) or mosquito cells, or alternately between the two. Initial characterization confirmed that fidelity mutants are attenuated in mosquito, but not avian, cells. Deep sequencing revealed mutations unique to both cell lines and fidelity mutants, including ENV G1378A, a mutation associated with avian cell adaptation. To characterize maintenance and adaptation, viral outputs were monitored throughout passaging and viral fitness was assessed. The results indicate that fidelity mutants can at times recover fitness during mosquito cell passage, but remain attenuated relative to WT. Despite similar initial fitness, LoFi mutants were impaired during sequential passage in avian cells. Conversely, HiFi mutants passaged in avian cells showed increased adaptation, suggesting that increased fidelity may be advantageous in avian hosts. Although some adaptation occurred with individual mutants, the output titres of fidelity mutants were on average lower and were often lost during host switching. These data confirm that arbovirus fidelity is likely fine-tuned to maximize survival in disparate hosts.
    Keywords:  West Nile virus; fidelity; flavivirus; host cycling; quasispecies; viral fitness
  16. PLoS One. 2020 ;15(2): e0226736
    Zhang D, Wang Y, He K, Yang Q, Gong M, Ji M, Chen L.
      BACKGROUND: Wolbachia has been reported to suppress a variety of pathogen infections in mosquitoes, but the mechanism is undefined. Two possibilities have been proposed. One is that Wolbachia activates host immune responses, and the other one is that Wolbachia competes with pathogens for limited nutrients.METHODOLOGY/PRINCIPAL FINDINGS: In this study, we compared host immune responses and the densities of two different strains of Wolbachia in naturally occurring parental and artificially created hybrid host genetic backgrounds. No significant difference in Wolbachia density was found between these hosts. We found that Wolbachia could activate host innate immune responses when the host genetic profile was different from that of its natural host. When these hosts were challenged with pathogenic bacteria, mosquitoes in new host-Wolbachia symbioses had a higher survival rate than in old host-Wolbachia symbioses.
    CONCLUSIONS/SIGNIFICANCE: The presence of Wolbachia per se does not necessarily affect pathogen infections, suggesting that a competition for limited nutrients is not the main reason for Wolbachia-mediated pathogen suppression. Instead, host immune responses are responsible for it. The elucidation of an immunity nature of PI is important to guide future practice: Wolbachia may be genetically engineered to be more immunogenic, it is desired to search and isolate more strains of Wolbachia, and test more host-Wolbachia symbioses for future applications. Our results also suggest Wolbachia-based PI may be applied to naturally Wolbachia-infected mosquito populations, and extend to the control of a broader range of mosquito-borne diseases.
  17. Malar J. 2020 Feb 21. 19(1): 83
    Aka KG, Traoré DF, Sagna AB, Zoh DD, Assi SB, Tchiekoi BN, Adja AM, Remoue F, Poinsignon A.
      BACKGROUND: In malaria-endemic areas, human populations are frequently exposed to immunomodulatory salivary components injected during mosquito blood feeding. The consequences on pathogen-specific immune responses are not well known. This study evaluated and compared the humoral responses specific to merozoite stage vaccine candidates of Plasmodium falciparum, in children differentially exposed to Anopheles bites in a natural setting.METHODS: The cross-sectional study was carried out in Bouaké (Côte d'Ivoire) where entomological data and blood samples from children (0-14 years) were collected in two sites with similar malaria prevalence. Antibody (IgG, IgG1, IgG3) responses to PfAMA1 and PfMSP1 were evaluated by ELISA. Univariate and multivariate analysis were performed to assess the relationship between the immune responses to P. falciparum antigens and exposure to Anopheles bites in the total cohort and in each site, separately. The individual level of exposure to Anopheles bites was evaluated by quantifying specific IgG response to the Anopheles gSG6-P1 salivary peptide, which represents a proxy of Anopheles exposure.
    RESULTS: The anti-Plasmodium humoral responses were different according to the level of exposure of children, with those highly exposed to Anopheles presenting significantly lower antibody responses to PfMSP1 in total population (IgG and IgG3) and in Petessou village (IgG, IgG1, IgG3). No significant difference was seen for PfAMA1 antigen between children differently exposed to Anopheles. In Dar-es-Salam, a neighbourhood where a high Culex density was reported, children presented very low antibody levels specific to both antigens, and no difference according to the exposure to Anopheles bites was found.
    CONCLUSION: These findings may suggest that immunomodulatory components of Anopheles saliva, in addition to other factors, may participate to the modulation of the humoral response specific to Plasmodium merozoite stage antigens. This epidemiological observation may form a starting point for additional work to decipher the role of mosquito saliva on the modulation of the anti-Plasmodium acquired immunity and clinical protection in combining both field and ex vivo immunological studies.
    Keywords:  Anopheles; Exposure; Immunity; Immunomodulation; Malaria; Plasmodium falciparum; Salivary proteins