Characterization of a Western Pacific Zika Virus Strain in Australian Aedes aegypti

Zika virus (ZIKV) is a globally emerging arbovirus responsible for widespread epidemics in the western Pacific, the Americas, and Asia. The virus predominately circulates in urban transmission cycles between Aedes aegypti and humans. Australia is considered at risk to outbreaks of ZIKV due to the presence of A. aegypti populations in northern areas of the state of Queensland. Furthermore, close proximity to epidemic regions has led to almost 50% of imported cases reported since 2012 originating in the Pacific region. We conducted the first vector competence experiments with A. aegypti from three Australian populations for a western Pacific strain of ZIKV. When exposed to bloodmeals containing between 10⁵ and 10⁸ tissue culture infectious dose (TCID)₅₀/mL of virus, infection, dissemination, and transmission, rates were <10%. In comparison to using frozen virus stock, exposing mosquitoes to freshly cultured virus also did not increase infection or transmission rates. It was only when bloodmeal titers exceeded 10⁸ TCID₅₀/mL that infection rates approached 50% and transmission rates increased to >20%. However, this concentration of virus is considerably higher than levels previously reported in blood samples from viremic humans. The Australian A. aegypti tested appear to express a midgut barrier to ZIKV infection, as 50% of mosquitoes that became infected developed a disseminated infection, and 50% of those mosquitoes transmitted the virus. Overall, these results suggest that while Australian A. aegypti strains are able to transmit the western Pacific ZIKV strain, they are relatively inefficient vectors of the virus.