Zika virus infection in asymptomatic persons in Myanmar, 2018

Abstract

Background Zika virus (ZIKV) is a mosquito-borne flavivirus. Outbreaks of ZIKV infection have occurred in Africa, Southeast Asia, the Pacific Islands, the Americas and the Caribbean. Although most ZIKV infections are asymptomatic, cases of neurological manifestations have been described. The aim of the present study was to identify the prevalence of ZIKV infection among the asymptomatic persons in Myanmar in 2018. Methods A total of 284 serum samples from apparently healthy persons were collected from Yangon, Myanmar in 2018. They were analysed for ZIKV infection by immunoglobulin M (IgM) capture enzyme-linked immunosorbent assay (ELISA), IgG indirect ELISA, 50% focus reduction neutralization test, real-time reverse transcription polymerase chain reaction (RT-PCR) and conventional RT-PCR. Results Of the 284 apparently healthy persons, 31.3% were positive for the presence of IgM against ZIKV and 94.3% were positive for anti-flavivirus IgG. Among the ZIKV IgM-positive samples, we confirmed ZIKV infection in 15.8% of asymptomatic persons by neutralization test and real-time RT-PCR. Conclusions We conclude that ZIKV infection was increasing among asymptomatic persons in the same area in Myanmar during 2018 compared with 2017. It is highly recommended to strengthen the surveillance system for ZIKV to prevent possible outbreaks.

Serological Evidence of Zika Virus Infection in Febrile Patients and Healthy Blood Donors in Sabah, Malaysian Borneo, 2017–2018

“…25 Contrary to the Malaysian results, a number of studies in Southeast Asia in Myanmar (15.8%), Laos (4.5%), Indonesia (9.9%), Cambodia (63%), and Thailand (70.4%) have reported relatively high rates of ZIKV seroprevalence among asymptomatic adults and children. 19,[26][27][28][29] In the present study of confirmed ZIKV cases, the IgM ratio was higher against ZIKV than DENV and JEV, with some samples indicating the presence of IgMs against ZIKV, DENV, and JEV, all of which belong to the same Flaviviridae family. This could be due to coinfection or sequential infection of the patients by DENV and ZIKV since they are transmitted by the same mosquito species circulating in the same area.…”

“…31 Consequently, an in-house ZIKV/DENV/JEV IgM-capture ELISA was used, followed by 90% neutralization tests against ZIKV, four serotypes of DENV, and JEV. 18,19 The neutralization test undoubtedly plays an important role in confirming ZIKV infections in this situation by determining ZIKV IgM crossreactive with other flaviviruses to rule out ZIKV infection. Zika virus IgM persists for up to approximately 12 weeks, 32 and positive ZIKV IgM was detected in apparently healthy people.…”

“…Serological confirmation of ZIKV, DENV, and JEV was obtained by an in-house IgM-capture ELISA as previously described. 18,19 In brief, 96-well microplates were coated with anti-human IgM goat IgG antibody (Cappel ICN Pharmaceuticals, Aurora, OH) for 4 C overnight and were blocked with Block Ace (UK-1 B 80, Yukijirushi, Sapporo, Japan). After washing the plates with PBS Tween (PBS-T), a 1:100 dilution of tested samples and positive and negative controls were distributed into duplicate wells.…”

“…To confirm the presence of a specific antibody for ZIKV, DENV, and JEV in febrile patients and healthy blood donors, serum samples were checked for the ability to neutralize ZIKV, the four serotypes of DENV, and JEV using a 90% focus reduction neutralization test (FRNT90), as described previously. 18,19 Serially diluted heattreated serum samples were mixed with equal volumes of each virus at 60 focus-forming units and were incubated at 37 C for 1 hour for the virus antibody neutralization reaction to occur. Vero cells were infected with a virus and serum mixture.…”

“…Once washed with PBS (-), the plates were fixed with 4% paraformaldehyde phosphate-buffered solution and were each permeabilized with 1% NP-40 solution at RT for 30 minutes. Pooled human serum samples with a high titer ($ 52,000) of anti-flavivirus IgG which recognized DENV, JEV, ZIKV 19,21,22 (diluted 1:1,500) were then added to each well and incubated at 37 C for 1 hour. After washing, 1:1,000 diluted HRP-conjugated goat anti-human IgG was added to each well at 37 C for 1 hour.…”