Serological evidence of possible high levels of undetected transmission of Zika virus among Papua New Guinea military personnel, 2019

OBJECTIVES: The Papua New Guinea (PNG) Health Department retrospectively reported six cases of Zika virus (ZIKV) from a cohort of febrile patients during outbreaks of dengue and malaria in 2016. However, the transmission of ZIKV remains unclear due to lack of testing capability. This study aimed to determine the level of immunity to ZIKV among PNG military personnel (PNGMP) in 2019. METHODS: Sera of 208 PNGMP recruited in April 2019 was tested for the presence of anti-ZIKV immunoglobulin G (IgG) and M (IgM) antibodies using Euroimmun IgG/IgM detection kits, and anti-ZIKV neutralizing antibody (Nab) against a ZIKV African strain on all anti-ZIKV-IgG/IgM(+) samples. RESULTS: Anti-ZIKV seropositivity of these sera was as follows: IgG, 67%; IgM, 9%; and Nab, 65%. Five of 19 anti-ZIKV-IgM(+) samples had anti-ZIKV-Nab titres ≥20, as well as an anti-ZIKV-Nab titre ratio ≥4 compared with the Nab titres of four anti-dengue serotypes, so met the criteria of the World Health Organization (WHO) for confirmed ZIKV infection. CONCLUSIONS: The prevalence of anti-ZIKV-Nab of 65% suggests that there are high levels of ZIKV exposure among PNGMP. Five of the 19 anti-ZIKV-IgM(+) samples met the WHO criteria for confirmed ZIKV infection, suggesting a recent undetected outbreak in PNGMP. These results provide better understanding of the current ZIKV epidemic status in PNGMP.