Australian arboviruses associated with undiagnosed undifferentiated febrile illness

There are at least 13 Australian arboviruses that have been associated with human infection but routine tests are not available to diagnose infection with most of these and their role in human pathology, undifferentiated febrile illness (UFI) or other serious diseases is unknown. Following the development of a commercial ELISA to diagnose Ross River virus infections, the number of cases in Australia rose from 20-50 per year to more than 9000 in 2016. The aim of this study was to determine how prevalent infection of humans with these “orphan” viruses was and whether any of them are the cause of UFI. Screening of 1000 age and gender stratified plasma samples from healthy blood donors for IgG antibodies against, Ross River, Barmah Forest, Alfuy, Kokobera, Stratford, Kunjin and Edge Hill viruses by indirect ELISA produced a large number of non-specific reactions so, an age and gender stratified sub-sample from the plasma panel was tested in plaque reduction neutralisation tests. Additionally, 492 UFIs samples from patients in northern Australia were screened by indirect immunofluorescence for the presence of IgM antibodies against these viruses. There was a linear increase in the prevalence of neutralising antibodies against these viruses with annual seroconversion rates of Ross River virus,1.4% (r2=0.7); Barmah Forest virus, 0.5% (r2=0.7); Kunjin virus, 0.4% (r2=0.7); Edge Hill virus, 0.4% (r2=0.5); Kokobera virus,0.3% (r2=0.9); Alfuy virus 0.2% (r2=0.5); Murray valley encephalitis virus, 0.1% (r2=0.3) and Stratford virus 0.6% (r2=0.9). Of the 492 samples from UFI patients 5.2% contained IgM antibodies against one or more of these Australian arboviruses: RRV (0.8%); BFV (0.4%); ALF (1.4%); EHV (1.8%); KOK (1.4%); KUNV (2.4%); MVE (1%); STRV (1.2%). These results suggest that a number of the “orphan” Australian arboviruses have been infecting humans at a regular rate for decades and some of them may be associated with UFIs. There should be ongoing, and systematic, testing of UFI patients for evidence of recent infection with these orphan arboviruses to determine how significant the burden of the disease they cause is.