The arboviruses including Dengue(DENV), Zika(ZIKV), Ross River(RRV), Chikungunya (CHIKV), Japanese encephalitis(JEV) and Barmah forest(BFV) can cause human disease outbreaks, but the possible circulation of these arboviruses in Papua New Guinea Defence Force(PNGDF) is not known. In April 2019, the Australian Malaria and Infectious Disease Institute, in conjunction with PNGDF Health Services, conducted an arbovirus population surveillance in PNGDF personnel. A total of 208 serum samples, 76 from Manus Island and 132 from Wewak, were collected. We used commercial made ELISA kits (DENV, RRV and BFV kits from Panbio; JEV, CHIKV and ZIKV kits from Euroimmun) for detecting human IgG/IgM antibodies for initial screening and micro-neutralization assay to confirm the exposure to these pathogens.
A total of ELISA sero-positivity, RRV IgG 89.9%(187/208) IgM 39.4%(82/208); BFV IgG 11.5%(24/208), IgM 1.9%(4/208); CHIKV IgG 46.6%(97/208), IgM 8.9%(11/124); JEV IgG 94.7%(197/208), IgM 29.8% (62/208); ZIKV IgG 52.9%(110/208), IgM 7.8% (9/116); DENV IgG 17.3%(36/208), IgM 8.7%(18/208), were observed. The repeated RRV IgG/IgM ELISA assay generated similar results. The proportion of samples exhibiting neutralizing antibody against RRV (strain-QML isolated from a patient in Queensland 2004) was 64.1% (132/206), BFV (prototype strain-BH2193 isolated in 1974) was 8.2%(17/206) and ZIKV(prototype strain-MR766 isolated in 1947) was 78.7%(140/178). Neutralization assays for other viruses are currently being conducted.
Our results demonstrated these six pathogens are silently endemic in PNGDF personnel. In comparison with that the reported seroprevalence in ostensibly healthy blood donors from Queensland conducted by Australian Blood Bank (using Panbio kits) of approximately 1.2% IgM and 1.7% IgG for BFV; and 0.9% IgM and 8.4% IgG for RRV, our results indicate that the exposure rate of PNGDF personnel to both Australian unique pathogens is much higher. The current commercially available ELISA detection kits for these six arboviruses may not suit for diagnostic purpose in the endemic areas such as PNG, due to the serological cross-reactivity among alphavirus and flavivirus. We cannot exclude the possibility of other alphavirus and flavivirus are endemic in PNG and cross-react with these six arboviruses in ELISA and neutralization assays. More serology and arbovirology surveillances are required in the Pacific Island countries and territories such as PNG.