Low seroprevalence rates of Zika virus in macaques and humans, Malaysia
Jamal I-Ching Sam1*, Yoke Fun Chan1, Chong Long Chua1, Magelda Montoya Cruz2, Andrew Pastor2, Jeffrine J. Rovie-Ryan3, Frankie Thomas Sitam3, Eva S.G. Soh Andu,1 Khebir Verasahib4, Eva Harris2*
1Department of Medical Microbiology, University Malaya, Kuala Lumpur, Malaysia; 2School of Public Health, University of California, Berkeley, USA; 3Department of Wildlife and National Parks Peninsular Malaysia, Kuala Lumpur, Malaysia; 4National Public Health Laboratory, Sungai Buloh, Malaysia
*Corresponding authors firstname.lastname@example.org, email@example.com)
Zika virus (ZIKV) has caused recent global outbreaks. The first isolation of ZIKV outside Africa was from Aedes aegypti in Malaysia in 1966. Since then, sporadic cases have been reported in Southeast Asia, but there has been only one outbreak, in Singapore in 2016. The reasons for the lack of ZIKV outbreaks in Southeast Asia, despite its likely endemicity (shown by historical seroprevalence studies), abundance of Ae. aegypti vectors, and recent heightened surveillance are unclear. We asked if endemicity in Malaysia would result in (1) sufficient human population immunity to limit significant outbreaks, and (2) evidence of sylavtic transmission in macaques, known reservoirs in Africa. We tested 1,086 residual serum samples collected in Kuala Lumpur in 2012 (before the Pacific outbreaks), August 2014 - March 2015 (early stages of the Americas outbreaks), and 2017 (after the outbreak in neighbouring Singapore), using a ZIKV NS1 blockade-of-binding ELISA assay with high sensitivity and specificity for detecting ZIKV IgG. Total seroprevalence was 7.0% (76/1,086; confirmation with neutralization assays underway) and was positively correlated with age. We also tested 234 wild long-tailed macaques (Macaca fasciularis) trapped in Peninsular Malaysia in 2009, 2010, and 2016; none were positive for ZIKV RNA, and the total seroprevalence of anti-ZIKV neutralizing antibodies was 1.3% (3/234). In summary, the low ZIKV seroprevalence in humans in Kuala Lumpur does not explain the low incidence of ZIKV cases and outbreaks. Other factors, such as the possible protective effects of pre-existing dengue immunity, should be explored. Long-tailed macaques are unlikely to be significantly involved in sylvatic cycles in Malaysia. We conclude that ZIKV endemicity in humans and macaques in Malaysia are at very low levels, and Malaysia remains at risk of epidemics.