Low Risk for Ross River Virus Infection in Expeditionary Forces Training in Australia Demonstrated by a Serological Survey of Marine Rotational Force-Darwin, 2012-2018.

On an annual basis, approximately 2,500 U.S. Marines and Sailors deploy to Australia on 6-month training rotations. Active duty personnel are generally immunologically naïve to pathogens endemic to tropical Australia, a vulnerability that could significantly impact medical readiness. To estimate risk, we screened 628 post-deployment serum samples by ELISA for serological evidence of infection with Ross River virus (RRV), a mosquito-borne alphavirus endemic to tropical Australia. Samples that tested above the negative cutoff value were paired with their pre-deployment samples to identify deployment-related seroconversion. These paired samples were further investigated with a live virus neutralization assay to assess specificity. There was a single RRV seroconversion and 49 false-positive results. In the context of these analyses (i.e., limited sample numbers collected between the months of March and October), we assess the RRV risk to MRFD as low and encourage strategies such as avoiding and preventing mosquito bites to mitigate the existing risk over widespread vaccination programs, if an FDA-approved vaccine becomes available. The Panbio RRV ELISA lacks the specificity to draw conclusions based on seropositivity from large-scale surveys of U.S. personnel.