Seroprevalence and associated risk factors of mosquito-borne alphaviruses in horses in northern Queensland.

OBJECTIVE

To investigate the seroprevalence and associated risk factors of alphaviruses (Ross River virus (RRV), Barmah Forest virus (BFV) and Whataroa virus (WHAV)) in northern Queensland horses.

METHODS

A cross-sectional study of alphavirus antibodies in horses (n = 287) from 147 properties in northern Queensland from September 2013 to June 2014 was conducted. Owners of sampled horses were interviewed on potential risk factors. Data were analysed for associations using multivariable logistic regression.

RESULTS

Antibody titres for RRV were demonstrated in samples from 134 properties (91%; 95% confidence interval (CI) 87-96%); 22 properties (15%) had BFV reactors (95% CI 12-18%) and 2 properties (1.4%) had WHAV reactors (95% CI -0.5-3.2%). The highest seroprevalence of RRV was in the Townsville-Burdekin region (93%; 95% CI 90-96%) followed by the Mackay-Whitsunday (90%; 95% CI 88-98%) and Far North Coast-Tableland (82%; 95% CI 74-90%) regions. No association (P ≤ 0.05) could be shown between any of the viruses and age groups, sexes, annual average temperature, degree of rainfall or proximity to wet environments. An association with reported large numbers of mosquitoes was seen for RRV but not BFV. A significant association between properties in close proximity to poultry and pigs was shown for BFV.

CONCLUSION

RRV is endemic within the horse population of northern Queensland, but horses exhibit few clinical signs and could play a role as amplifying hosts in the tropics. Exposure of horses to BFV is significant in northern Queensland and it should be considered a differential diagnosis for RRV. WHAV warrants further study.