Wolbachia enhances insect-specific flavivirus infection in Aedes aegypti mosquitoes.

Mosquitoes transmit a diverse group of human flaviviruses including West Nile, dengue, yellow fever, and Zika viruses. Mosquitoes are also naturally infected with insect-specific flaviviruses (ISFs), a subgroup of the family not capable of infecting vertebrates. Although ISFs are not medically important, they are capable of altering the mosquito's susceptibility to flaviviruses and may alter host fitness. Wolbachia is an endosymbiotic bacterium of insects that when present in mosquitoes limits the replication of co-infecting pathogens, including flaviviruses. Artificially created Wolbachia-infected Aedes aegypti mosquitoes are being released into the wild in a series of trials around the globe with the hope of interrupting dengue and Zika virus transmission from mosquitoes to humans. Our work investigated the effect of Wolbachia on ISF infection in wild-caught Ae. aegypti mosquitoes from field release zones. All field mosquitoes were screened for the presence of ISFs using general degenerate flavivirus primers and their PCR amplicons sequenced. ISFs were found to be common and widely distributed in Ae. aegypti populations. Field mosquitoes consistently had higher ISF infection rates and viral loads compared to laboratory colony material indicating that environmental conditions may modulate ISF infection in Ae. aegypti. Surprisingly, higher ISF infection rates and loads were found in Wolbachia-infected mosquitoes compared to the Wolbachia-free mosquitoes. Our findings demonstrate that the symbiont is capable of manipulating the mosquito virome and that Wolbachia-mediated viral inhibition is not universal for flaviviruses. This may have implications for the Wolbachia-based DENV control strategy if ISFs confer fitness effects or alter mosquito susceptibility to other flaviviruses.

The Transcriptional Response of Aedes aegypti with Variable Extrinsic Incubation Periods for Dengue Virus.

Dengue fever is the most prevalent arboviral disease globally. Dengue virus is transmitted primarily by the Aedes aegypti mosquito. One measure of the mosquito's efficiency as a vector is the extrinsic incubation period (EIP), which is the time between the ingestion of viremic blood and the emergence of virions in the saliva. The longer it takes virus to infect the midgut and traverse to the saliva, the fewer opportunities the mosquito will have to transmit the pathogen over its lifetime. We have shown previously that EIP for dengue virus is highly heritable and that it is negatively correlated with vector lifespan. Here, we examined the transcriptional profiles for mosquitoes that varied in their EIP phenotype and identified pathways associated with either short or long EIP. We found that mosquitoes with short EIP have less active immune responses but higher levels of protein translation and calcium ion homeostasis and that mosquitoes with longer EIP may have slower metabolism. These findings indicate a complex interplay between calcium ion distribution, ribosome biogenesis, and metabolism and reveal potential pathways that could be modified to slow the rate of viral progression and hence limit lifetime transmission capability.