TRACKING ROSS RIVER VIRUS HOST DIVERSITY USING MOSQUITOES AS 'FLYING SYRINGES'

Abstract

Intro: Ross River virus (RRV) is a multi-vector, multi-host pathogen, responsible for most notifications of human arboviral infections in Australia. Despite regular outbreaks, the most important vectors and hosts that drive transmission cycles are not known. Recent studies have shown that whilst marsupials are competent reservoirs of RRV, there is potential for placental mammals and birds to contribute to transmission dynamics, although their role in maintaining the virus is still unclear. We aimed to use mosquitoes and their blood meals as the sampling tool for exploring vector‐host dynamics and RRV epidemiology. Methods: We combined mosquito surveys with molecular and serological assays to investigate transmission pathways across five urban sites in Brisbane, Australia. We identified host origins of mosquito blood meals through amplification and sequencing of the Cytochrome b gene. In addition, mosquito blood meals were assessed for the presence of antibodies to RRV using a micro- plaque reduction neutralisation test (mPRNT). Findings: A total of 480 blood-fed mosquitoes were collected from March 2021 to May 2022. These included mainly Culex annulirostris (68.7%) and Cx. orbostiensis (9.4%). Blood meals of 307 mosquitoes were identified mainly as humans (52%) and cattle (6.8%). RRV seroprevalence was 71% in 21 samples from cattle and 52% in 253 samples of human origin. Discussion: Relatively high RRV seroprevalence in humans indicates high rates of exposure. The high proportion of human blood in mosquito blood meals may reflect host availability in the study area. It also contrasts with previous Australian studies in which humans represented a relatively small proportion of meals. Conclusion: Our results show that mosquitoes may be used to derive species- specific information on vectors, reservoirs and pathogen exposure, which can help identify potential transmission pathways. It also provides a novel, non- invasive method of estimating seroprevalence in both humans and wildlife.