Risk of urban Mayaro virus (Alphavirus: Togaviridae) transmission: is Aedes aegypti a competent vector?

Mayaro virus (MAYV) is an emerging pathogen endemic in Latin America and is the causative agent of fever and polyarthritis. Urban transmission depends on its ability to be transmitted by Aedes aegypti and to be amplified by humans. The aim of this study was to evaluate the susceptibility to infection and transmission and the presence of barriers to infection in different populations of Ae. aegypti for MAYV. Ae. aegypti eggs were collected from Cordoba, Buenos Aires and Rosario Cities (Argentina). Females were infected with five viral loads of MAYV strain (1 to 6 log10 PFU/ml) and maintained for 8 days. The presence of infectious viral particles in body, legs, and saliva was detected by plaquing assay in Vero cell monolayers. Through a bibliographic search, Ae. aegypti population data from Peru were incorporated and tested with different viral doses of MAYV. We build dose-response curves for Ae. aegypti populations to estimate infection (IR), dissemination (DR) and transmission (TR) based on MAYV viral loads detected in humans to estimate transmission risk occurring in an urban environment. The overall IR and DR were significantly associated with the viral doses and were not significantly affected by population origin. We found IR ranging for 3 to 84% (ID50% were higher than 5.5 log10 PFU/ml) and a DR reached 78% (DD50% higher than 6.0 log10 PFU/ml). The percentage of dissemination based on the infected mosquitoes ranged from 60 to 86% while the percentage of transmission based on disseminated mosquitoes ranged from 11 to 60%. Our results indicate that Ae. aegypti populations are not competent vectors for MAYV because they need higher viral doses than those developed by humans (3.9 - 4.5 log10 PFU/ml) to become infected. Only a very low proportion of infected mosquitoes with high 5 log10 PFU/ml are capable of transmitting it.