Neglected Australian arboviruses associated with undiagnosed undifferentiated febrile illness

Australia is home to over 75 arthropod-borne viruses, with least 13 associated with human infection. Ross River (RRV), Barmah Forest (BFV), Murray Valley encephalitis (MVEV) and Kunjin (KUNV) viruses commonly cause disease and are diagnosed in pathology laboratories. Following commercial ELISA development to diagnose RRV, in 2016 cases exceeded 9,000. However, other indigenous arboviruses, such as Alfuy (ALFV), Edge Hill (EHV), Kokobera (KOKV), Sindbis (SINV) and Stratford (STRV), are not routinely tested. Little is known of their role in human pathology, undifferentiated febrile illness (UFI) or serious diseases. This study aimed to determine prevalence of infection of humans with these neglected Australian arboviruses and whether any causes UFI. Screening of 1,000 age- and gender-stratified plasma samples from healthy Queensland-resident blood donors for antiviral IgG antibodies by indirect ELISA produced non-specific reactivity so a sub-sample was tested by plaque reduction neutralisation. 492 acute-phase samples from UFI patients in northern Australia were also screened by indirect immunofluorescence for virus-specific IgM antibodies. There was a linear increase in prevalence of neutralising antibodies with annual seroconversion rates ranging from RRV 1.3% to KOKV and STRV 0.05%. Among UFI patient samples 5.2% contained IgM against one or more of: RRV 0.8%; BFV 0.4%; ALF 1.4%; EHV 1.8%; KOKV 1.4%; KUNV 2.4%; MVEV 1.0%; STRV 1.2%. No age-dependent anti-ALFV antibodies prevalence was observed. A small proportion of UFI was attributable to infection; 2 ALFV, 4 EHV, 14 KOKV, 8 KUNV, 8 MVEV and 1 STRV identified cases per 1000 persons tested. These results indicate several neglected Australian arboviruses have been infecting humans for decades and some may be associated with UFI. A program of systematic testing of UFI patients is recommended to examine for recent infection to determine the significance of the burden of the disease that these neglected arboviruses cause.