High prevalence of canine heartworm, Dirofilaria immitis, in pet dogs in south Texas, USA, with evidence of Aedes aegypti mosquitoes contributing to transmission.

BACKGROUND: The canine heartworm Dirofilaria immitis, a filarioid nematode of dogs and other carnivores, is widespread in the USA and the world. Over 20 different mosquito species serve as intermediate hosts of D. immitis, but their contribution to transmission varies according to factors like host feeding patterns, geographic locations and climatic conditions. The yellow fever mosquito, Aedes aegypti, is a competent vector of D. immitis but is often dismissed as a vector of veterinary relevance given its anthropophilic feeding behavior. We evaluated the prevalence of D. immitis in pet dogs along the USA-Mexico border and assessed whether Ae. aegypti in the area are naturally infected with heartworm and are potentially acting as a vector. METHODS: A total of 200 whole blood samples collected from pet dogs in the Lower Rio Grande Valley in south Texas from 2016 to 2019 were included in this study. Canine serum samples for D. immitis were tested using the DiroCHEK® Canine Heartworm Antigen Test Kit pre- and post-immune complex dissociations (ICD) and blood samples were tested using high-resolution melt (HRM) quantitative PCR (qPCR) and a probe-based qPCR. Additionally, mosquito specimens were collected and identified, and Ae. aegypti heads, abdomens and pools were tested using conventional PCR (cPCR) and HRM qPCR. RESULTS: Overall, heartworm prevalence in dogs aged > 6 months was 40.8% (64/157) when the results from all testing modalities were considered. Heartworm antigen was detected in 33.5% and 40.7% of the dogs using DiroCHEK® pre- and post-ICD, respectively. By molecular screening, 20.1% of dogs tested positive with probe-based qPCR, while only one tested positive with HRM qPCR. Of the Ae. aegypti abdomens from blood-fed Ae. aeygpti tested, 20 (21.7%) from mosquitoes that fed on dogs and four (7%) from those that fed on humans tested positive for heartworm. Among Ae. aegypti heads from blood-fed Ae. aeygpti, two (1.1%) were positive based on cPCR and four (2.5%) were positive based on HRM qPCR. No D. immitis DNA was detected in the 208 pools of whole bodies (358 individuals) of Ae. aegypti gravid females. CONCLUSIONS: Our study highlights a high prevalence of heartworm in dogs in south Texas and provides evidence that Ae. aegypti could be contributing to heartworm transmission in canine populations in this region.

Robust network stability of mosquitoes and human pathogens of medical importance.

BACKGROUND: The exact number of mosquito species relevant to human health is unknown, posing challenges in understanding the scope and breadth of vector-pathogen relationships, and how resilient mosquito vector-pathogen networks are to targeted eradication of vectors. METHODS: We performed an extensive literature survey to determine the associations between mosquito species and their associated pathogens of human medical importance. For each vector-pathogen association, we then determined the strength of the associations (i.e., natural infection, lab infection, lab dissemination, lab transmission, known vector). A network analysis was used to identify relationships among all pathogens and vectors. Finally, we examined how elimination of either random or targeted species affected the extinction of pathogens. RESULTS: We found that 88 of 3578 mosquito species (2.5%) are known vectors for 78 human disease-causing pathogens; however, an additional 243 species (6.8%) were identified as potential or likely vectors, bringing the total of all mosquitos implicated in human disease to 331 (9.3%). Network analysis revealed that known vectors and pathogens were compartmentalized, with the removal of six vectors being enough to break the network (i.e., cause a pathogen to have no vector). However, the presence of potential or likely vectors greatly increased redundancies in the network, requiring more than 41 vectors to be eliminated before breaking the network. CONCLUSION: Although < 10% of mosquitoes are involved in transmitting pathogens that cause human disease, our findings point to inherent robustness in global mosquito vector-pathogen networks.

Meta-Analysis of the Relative Abundance of Nuisance and Vector Mosquitoes in Urban and Blue-Green Spaces.

Blue-green spaces (BGSs), urban areas characterized by the presence of vegetation and or water, and infrastructure form a potential solution for public health threats from increasing urbanization. We conducted a meta-analysis to test the hypothesis that blue-green spaces increase the abundance of nuisance and vector mosquito species compared to non-greened urban areas. After screening 7306 studies published since 1992, we identified 18 studies containing sufficient data from both traditional urban areas and BGSs. We found no significant difference in mean abundance of all mosquito taxa in three genera (Aedes, Culex, Anopheles) when comparing blue-green spaces and non-greened urban spaces. Similarly, a separate analysis of each individual genera found no significant differences. An analysis of the taxa by larval habitat guilds found no differences for container-breeding mosquitoes. Flood-water species tended to be more abundant in blue-green spaces, but the differences were not significant. The individual taxa of Aedes albopictus and the Culex pipiens complex showed no differences between blue-green and urban spaces, while the abundance of Aedes aegypti was significantly higher in traditional urban spaces. Due to the variety existing between and among the several types of blue-green spaces, further studies comparing each unique type of blue-green space or infrastructure will be necessary to draw conclusions regarding the influence of each structure on for urban mosquito communities.

Mosquitoes (Diptera: Culicidae) on the islands of Puerto Rico and Vieques, U.S.A.

We conducted an island-wide survey of the Caribbean islands Puerto Rico and Vieques, U.S.A. during late 2018 and early 2019 to document the current richness of mosquitoes (Diptera: Culicidae). We used a combination of larval surveys and adult trapping using baited CDC light traps and BG-Sentinel traps across 41 of the 78 municipalities. We collected 9 genera, 12 subgenera, and 31 species, which when combined with past studies yields 44 species on the islands. We also note species occurrences across habitat types and elevations from around the islands. One new record, Aedes (Ochlerotatus) obturbator Dyar and Knab, is noted. However we found no evidence of the presence of Aedes albopictus (Skuse), an invasive found throughout the Caribbean, or Aedes (Fredwardsius) vittatus (Bigot), an exotic species recently reported in the Dominican Republic and Cuba. Habitat associations and information regarding the medical importance of species are also included. Given that the islands often experience outbreaks of several arboviruses, obtaining a complete picture of the species present is of high importance.

Honey Bee Viruses in Wild Bees: Viral Prevalence, Loads, and Experimental Inoculation.

Evidence of inter-species pathogen transmission from managed to wild bees has sparked concern that emerging diseases could be causing or exacerbating wild bee declines. While some pathogens, like RNA viruses, have been found in pollen and wild bees, the threat these viruses pose to wild bees is largely unknown. Here, we tested 169 bees, representing 4 families and 8 genera, for five common honey bee (Apis mellifera) viruses, finding that more than 80% of wild bees harbored at least one virus. We also quantified virus titers in these bees, providing, for the first time, an assessment of viral load in a broad spectrum of wild bees. Although virus detection was very common, virus levels in the wild bees were minimal-similar to or lower than foraging honey bees and substantially lower than honey bees collected from hives. Furthermore, when we experimentally inoculated adults of two different bee species (Megachile rotundata and Colletes inaequalis) with a mixture of common viruses that is lethal to honey bees, we saw no effect on short term survival. Overall, we found that honey bee RNA viruses can be commonly detected at low levels in many wild bee species, but we found no evidence that these pathogens cause elevated short-term mortality effects. However, more work on these viruses is greatly needed to assess effects on additional bee species and life stages.

Bee Abundance and Nutritional Status in Relation to Grassland Management Practices in an Agricultural Landscape.

Grasslands provide important resources for pollinators in agricultural landscapes. Managing grasslands with fire and grazing has the potential to benefit plant and pollinator communities, though there is uncertainty about the ideal approach. We examined the relationships among burning and grazing regimes, plant communities, and Bombus species and Apis mellifera L. abundance and nutritional indicators at the Grand River Grasslands in southern Iowa and northern Missouri. Treatment regimes included burn-only, grazed-and-burned, and patch-burn graze (pastures subdivided into three temporally distinct fire patches with free access by cattle). The premise of the experimental design was that patch-burn grazing would increase habitat heterogeneity, thereby providing more diverse and abundant floral resources for pollinators. We predicted that both bee abundance and individual bee nutritional indicators (bee size and lipid content) would be positively correlated with floral resource abundance. There were no significant differences among treatments with respect to bee abundance. However, some of the specific characteristics of the plant community showed significant relationships with bee response variables. Pastures with greater abundance of floral resources had greater bee abundance but lower bee nutritional indicators. Bee nutritional variables were positively correlated with vegetation height, but, in some cases, negatively correlated with stocking rate. These results suggest grassland site characteristics such as floral resource abundance and stocking rate are of potential importance to bee pollinators and suggest avenues for further research to untangle the complex interactions between grassland management, plant responses, and bee health.