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1. Not all mosquitoes are created equal: A synthesis of vector competence experiments reinforces virus associations of Australian mosquitoes

   https://doi.org/10.1371/journal.pntd.0010768  

   Kain, Morgan P. ; Skinner, Eloise B. ; Athni, Tejas S. ; Ramirez, Ana L. ; Mordecai, Erin A. ; van den Hurk, Andrew F. ( October 2022 , PLOS Neglected Tropical Diseases)

   Brackney, Doug E. (Ed.)

   The globalization of mosquito-borne arboviral diseases has placed more than half of the human population at risk. Understanding arbovirus ecology, including the role individual mosquito species play in virus transmission cycles, is critical for limiting disease. Canonical virus-vector groupings, such as Aedes - or Culex -associated flaviviruses, have historically been defined using virus detection in field-collected mosquitoes, mosquito feeding patterns, and vector competence, which quantifies the intrinsic ability of a mosquito to become infected with and transmit a virus during a subsequent blood feed. Herein, we quantitatively synthesize data from 68 laboratory-based vector competence studies of 111 mosquito-virus pairings of Australian mosquito species and viruses of public health concern to further substantiate existing canonical vector-virus groupings and quantify variation within these groupings. Our synthesis reinforces current canonical vector-virus groupings but reveals substantial variation within them. While Aedes species were generally the most competent vectors of canonical “ Aedes -associated flaviviruses” (such as dengue, Zika, and yellow fever viruses), there are some notable exceptions; for example, Aedes notoscriptus is an incompetent vector of dengue viruses. Culex spp. were the most competent vectors of many traditionally Culex -associated flaviviruses including West Nile, Japanese encephalitis and Murray Valley encephalitis viruses, although some Aedes spp. are also moderately competent vectors of these viruses. Conversely, many different mosquito genera were associated with the transmission of the arthritogenic alphaviruses, Ross River, Barmah Forest, and chikungunya viruses. We also confirm that vector competence is impacted by multiple barriers to infection and transmission within the mesenteron and salivary glands of the mosquito. Although these barriers represent important bottlenecks, species that were susceptible to infection with a virus were often likely to transmit it. Importantly, this synthesis provides essential information on what species need to be targeted in mosquito control programs. 

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2. Household and climate factors influence Aedes aegypti presence in the arid city of Huaquillas, Ecuador

   https://doi.org/10.1371/journal.pntd.0009931  

   Martin, James L. ; Lippi, Catherine A. ; Stewart-Ibarra, Anna M. ; Ayala, Efraín Beltrán ; Mordecai, Erin A. ; Sippy, Rachel ; Heras, Froilán Heras ; Blackburn, Jason K. ; Ryan, Sadie J. ( November 2021 , PLOS Neglected Tropical Diseases)

   Barrera, Roberto (Ed.)

   Arboviruses transmitted by Aedes aegypti (e.g., dengue, chikungunya, Zika) are of major public health concern on the arid coastal border of Ecuador and Peru. This high transit border is a critical disease surveillance site due to human movement-associated risk of transmission. Local level studies are thus integral to capturing the dynamics and distribution of vector populations and social-ecological drivers of risk, to inform targeted public health interventions. Our study examines factors associated with household-level Ae . aegypti presence in Huaquillas, Ecuador, while accounting for spatial and temporal effects. From January to May of 2017, adult mosquitoes were collected from a cohort of households (n = 63) in clusters (n = 10), across the city of Huaquillas, using aspirator backpacks. Household surveys describing housing conditions, demographics, economics, travel, disease prevention, and city services were conducted by local enumerators. This study was conducted during the normal arbovirus transmission season (January—May), but during an exceptionally dry year. Household level Ae . aegypti presence peaked in February, and counts were highest in weeks with high temperatures and a week after increased rainfall. Univariate analyses with proportional odds logistic regression were used to explore household social-ecological variables and female Ae . aegypti presence. We found that homes were more likely to have Ae . aegypti when households had interruptions in piped water service. Ae . aegypti presence was less likely in households with septic systems. Based on our findings, infrastructure access and seasonal climate are important considerations for vector control in this city, and even in dry years, the arid environment of Huaquillas supports Ae . aegypti breeding habitat. 

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3. Indoor Resting Behavior of Aedes aegypti (Diptera: Culicidae) in Acapulco, Mexico

   https://doi.org/10.1093/jme/tjw203  

   Dzul-Manzanilla, Felipe ; Ibarra-L?pez, J?sus ; Bibiano Mar?n, Wilbert ; Martini-Jaimes, Andr?s ; Leyva, Joel Torres ; Correa-Morales, Fabi?n ; Huerta, Her?n ; Manrique-Saide, Pablo ; Prokopec, Gonzalo Vazquez ( June 2017 , Journal of Medical Entomology)

   The markedly anthropophilic and endophilic behaviors of Aedes aegypti (L.) make it a very efficient vector of dengue, chikungunya, and Zika viruses. Although a large body of research has investigated the immature habitats and conditions for adult emergence, relatively few studies have focused on the indoor resting behavior and distribution of vectors within houses. We investigated the resting behavior of Ae. aegypti indoors in 979 houses of the city of Acapulco, Mexico, by performing exhaustive indoor mosquito collections to describe the rooms and height at which mosquitoes were found resting. In total, 1,403 adult and 747 female Ae. aegypti were collected, primarily indoors (98% adults and 99% females). Primary resting locations included bedrooms (44%), living rooms (25%), and bathrooms (20%), followed by kitchens (9%). Aedes aegypti significantly rested below 1.5 m of height (82% adults, 83% females, and 87% bloodfed females); the odds of finding adult Ae. aegypti mosquitoes below 1.5 m was 17 times higher than above 1.5 m. Our findings provide relevant information for the design of insecticide-based interventions selectively targeting the adult resting population, such as indoor residual spraying. 

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4. Extreme infectious titer variability in individual Aedes aegypti mosquitoes infected with Sindbis virus is associated with both differences in virus population structure and dramatic disparities in specific infectivity

   https://doi.org/10.1371/journal.ppat.1012047  

   Hodoameda, Peter ; Ebel, Gregory D ; Mukhopadhyay, Suchetana ; Clem, Rollie J ( February 2024 , PLOS Pathogens)

   Goodman, Alan G (Ed.)

   Variability in how individuals respond to pathogens is a hallmark of infectious disease, yet the basis for individual variation in host response is often poorly understood. The titer of infectious virus among individual mosquitoes infected with arboviruses is frequently observed to vary by several orders of magnitude in a single experiment, even when the mosquitoes are highly inbred. To better understand the basis for this titer variation, we sequenced populations of Sindbis virus (SINV) obtained from individual infectedAedes aegyptimosquitoes that, despite being from a highly inbred laboratory colony, differed in their titers of infectious virus by approximately 10,000-fold. We observed genetic differences between these virus populations that indicated the virus present in the midguts of low titer mosquitoes was less fit than that of high titer mosquitoes, possibly due to founder effects that occurred during midgut infection. Furthermore, we found dramatic differences in the specific infectivity or SI (the ratio of infectious units/viral genome equivalents) between these virus populations, with the SI of low titer mosquitoes being up to 10,000-fold lower than that of high titer mosquitoes. Despite having similar amounts of viral genomes, low titer mosquitoes appeared to contain less viral particles, suggesting that viral genomes were packaged into virions less efficiently than in high titer mosquitoes. Finally, antibiotic treatment, which has been shown to suppress mosquito antiviral immunity, caused an increase in SI. Our results indicate that the extreme variation that is observed in SINV infectious titer between individualAe.aegyptimosquitoes is due to both genetic differences between virus populations and to differences in the proportion of genomes that are packaged into infectious particles.

    

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5. Culex tarsalis Is a Competent Host of the Insect-Specific Alphavirus Eilat Virus (EILV)

   https://doi.org/10.1128/jvi.01960-22  

   Joseph, Renuka E. ; Urakova, Nadya ; Werling, Kristine L. ; Metz, Hillery C. ; Montanari, Kaylee ; Rasgon, Jason L. ( May 2023 , Journal of Virology)

   Heise, Mark T. (Ed.)

   ABSTRACT Eilat virus (EILV) is an insect-specific alphavirus that has the potential to be developed into a tool to combat mosquito-borne pathogens. However, its mosquito host range and transmission routes are not well understood. Here, we fill this gap by investigating EILV’s host competence and tissue tropism in five mosquito species: Aedes aegypti , Culex tarsalis , Anopheles gambiae , Anopheles stephensi , and Anopheles albimanus . Of the tested species, C. tarsalis was the most competent host for EILV. The virus was found in C. tarsalis ovaries, but no vertical or venereal transmission was observed. Culex tarsalis also transmitted EILV via saliva, suggesting the potential for horizontal transmission between an unknown vertebrate or invertebrate host. We found that reptile (turtle and snake) cell lines were not competent for EILV infection. We tested a potential invertebrate host ( Manduca sexta caterpillars) but found they were not susceptible to EILV infection. Together, our results suggest that EILV could be developed as a tool to target pathogenic viruses that use Culex tarsalis as a vector. Our work sheds light on the infection and transmission dynamics of a poorly understood insect-specific virus and reveals it may infect a broader range of mosquito species than previously recognized. IMPORTANCE The recent discovery of insect-specific alphaviruses presents opportunities both to study the biology of virus host range and to develop them into tools against pathogenic arboviruses. Here, we characterize the host range and transmission of Eilat virus in five mosquito species. We find that Culex tarsalis —a vector of harmful human pathogens, including West Nile virus—is a competent host of Eilat virus. However, how this virus is transmitted between mosquitoes remains unclear. We find that Eilat virus infects the tissues necessary for both vertical and horizontal transmission—a crucial step in discerning how Eilat virus maintains itself in nature. 

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