Incidence of Zika Virus Infection from a Dengue Epidemiological Study of Children in Ratchaburi Province, Thailand

Zika virus (ZIKV) is the mosquito-transmitted virus that the WHO declared a Public Health Emergency of International Concern in 2016 due to the consequence of microcephaly from infected pregnancies. The incidence of Zika infection has been unclear in many countries because most infected people have nonspecific febrile illnesses. This study’s aim is to investigate the incidence of symptomatic Zika virus infections from the archived samples of a dengue cohort study of children in central Thailand from 2006 to 2009. We performed Zika NS1 immunoglobulin (Ig)G enzyme-linked immunosorbent assay (ELISA) screening to identify symptomatic Zika infections in paired acute/convalescent serum samples. Symptomatic Zika infections were confirmed by reverse transcription polymerase chain reactions (RT-PCR) of acute serum samples. The comparison of the Zika NS1 IgG ELISA results between acute and convalescent samples showed 290/955 (30.4%) seropositive cases. Zika RT-PCR results were positive in 28 febrile cases (15 females, 13 males). Zika RT-PCR showed that symptomatic Zika infection occurred in children aged 4–11 years in Ratchaburi province, Thailand (2007–2009, first case in April 2007), and the symptomatic Zika:dengue infection ratio was 28 Zika:394 dengue (1:14). Phylogenetic analysis showed that all Zika viruses were of Asian lineage. Zika NS1 IgG ELISA identified Zika-infected patients and showed a low Zika:dengue ratio

Combining Immunoassays to Identify Zika Virus Infection in Dengue-Endemic Areas

Zika virus (ZIKV) is a mosquito-borne flavivirus that has recently emerged as a global health threat. The rise in ZIKV infections has driven an increased incidence of neonates born with microcephaly or other neurological malformations. Therefore, screening for ZIKV infection can considerably impact pregnant women, especially during the first trimester. The majority of ZIKV infections are mild or asymptomatic, and clinical diagnosis is inaccurate. Moreover, given the high level of cross-reactivity among flaviviruses, serological approaches to distinguish ZIKV from dengue virus (DENV) infections are complicated. We used the combination of DENV and ZIKV nonstructural protein 1 (NS1) IgG enzyme-linked immunosorbent assay (ELISA) and ZIKV NS1 blockade-of-binding (BOB) ELISA to test the convalescent sera of non-flavivirus, primary DENV, secondary DENV, and ZIKV infections. Our findings indicate that primary testing using a ZIKV NS1 IgG ELISA, the test of choice for large-scale ZIKV serosurvey studies, provided relatively high sensitivity. Moreover, the confirmation of positive ELISA results using the ZIKV NS1 BOB ELISA increased average specificity to 94.59% across serum samples. The combined use of two simple ELISAs for ZIKV serosurveys and the monitoring of ZIKV infection during pregnancy can elucidate the epidemiology, pathogenesis, and complications of ZIKV in DENV-endemic areas

Association between nutritional status and dengue severity in Thai children and adolescents.

Most cases of dengue virus infection are mild, but severe cases can be fatal. Therefore, identification of factors associated with dengue severity is essential to improve patient outcomes and reduce mortality. The objective of this study was to assess associations between nutritional status and dengue severity among Thai children and adolescents. This retrospective cross-sectional study was based on the medical records of 355 patients with dengue treated at the Hospital for Tropical Disease (Bangkok, Thailand) from 2017 to 2019. Subjects were Thai children aged less than 18 years with dengue virus infection confirmed by positive NS1 antigen or IgM. The 1997 and 2009 World Health Organization (WHO) dengue classifications were used to define disease severity and body mass index for age while the WHO growth chart was used to classify nutritional status. The proportions of patients with dengue fever who were underweight, normal weight, and overweight were 8.8%, 61.5%, and 29.7%, respectively. The proportions of patients with dengue haemorrhagic fever (DHF) who were underweight, normal weight, and overweight were 10.2%, 66.1%, and 23.7%, respectively. The proportions of patients with non-severe dengue who were underweight, normal weight, and overweight were 8.6%, 60.9%, and 30.5%, respectively; the same proportions of patients with severe dengue were 10.5%, 67.1%, and 22.4%, respectively. Higher proportions of patients with severe plasma leakage (DHF grade III and IV) were overweight compared with those with mild plasma leakage (DHF grade I and II) (45.5% vs. 18.8%). No difference in nutritional status was observed in patients with different dengue severity

Stability and infectivity of enteroviruses on dry surfaces: Potential for indirect transmission control

Hand, foot, and mouth disease (HFMD) is a contagious disease mainly occurring in young children, and outbreaks commonly occur among young children in the Asia–Pacific region including Thailand. Moreover, the World Health Organization (WHO) monitors HFMD in the Western Pacific region to detect outbreaks and other significant events by the Regional Event Based Surveillance System. HFMD is mainly caused by a group of enteroviruses (EVs) transmitted through direct contact (person to person) and indirect contact with contaminated objects (surface-to-hand). However, few studies have examined the surface stability of EVs. In this study, we investigated the stability of enterovirus A71 (EV-A71) and coxsackievirus A16 (CVA16) on three different dry surfaces (wood, plastic, and stainless steel) using the endpoint titration using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) staining of viable cells and real-time polymerase chain reaction (viral genome detection). The results revealed that virus infectivity dramatically decreased within a few hours on dry surfaces. However, viral RNA could be detected on dry surfaces for up to 28 days. Concerning heat inactivation, both EV-A71 and CVA16 were inactivated after exposure to 60°C for 15 min. Information on virus stability on different dry surfaces will provide useful information for HFMD transmission control

Arbovirus Seroprevalence Study in Bangphae District, Ratchaburi Province, Thailand: Comparison between ELISA and a Multiplex Rapid Diagnostic Test (Chembio DPP^® ZCD IgG)

Arboviruses, particularly dengue virus (DENV), Zika virus (ZIKV), and Chikungunya virus (CHIKV), pose a growing threat to global public health. For disease burden estimation and disease control, seroprevalence studies are paramount. This study was performed to determine the prevalence of DENV, ZIKV, and CHIKV on healthy individuals aged from 1–55 years old in Bangphae district, Ratchaburi province, Thailand. Enzyme-linked immunosorbent assays (ELISAs) and rapid diagnostic tests (RDTs) were performed on archived samples from a dengue serological survey conducted from 2012–2015. All 2012 samples had been previously tested using an anti-DENV immunoglobulin (Ig)G ELISA, and 400 randomly selected samples stratified by age, sex, and residential area were assessed by an in-house anti-ZIKV IgG ELISA and a commercial anti-CHIKV IgG ELISA to determine virus-specific antibody levels. An RDT (Chembio DPP® ZCD IgM/IgG System) was also used to investigate the presence of antibodies against DENV, ZIKV, or CHIKV. The ELISA results indicate that the seroprevalences of DENV, ZIKV, and CHIKV were 84.3%, 58.0%, and 22.5%, respectively. The youngest age group had the lowest seroprevalence for all three arboviruses, and the seroprevalences for these viruses were progressively higher with increasing participant age. The DPP® IgG sensitivities, as compared with ELISAs, for DENV, ZIKV, and CHIKV were relatively low, only 43.92%, 25.86%, and 37.78%, respectively. The ELISA results indicate that 16% of the study population was seropositive for all three viruses. DENV had the highest seroprevalence. ZIKV and CHIKV were also circulating in Bangphae district, Ratchaburi province, Thailand. The DPP® ZCD rapid test is not sensitive enough for use in seroprevalence studies