A Serosurvey of Japanese Encephalitis Virus in Monkeys and Humans Living in Proximity in Thailand.

Japanese encephalitis virus (JEV) is a member of the Flaviviridae family and one of Asia's most common causes of encephalitis. JEV is a zoonotic virus that is transmitted to humans through the bite of infected mosquitoes of the Culex species. While humans are dead-end hosts for the virus, domestic animals such as pigs and birds are amplification hosts. Although JEV naturally infected monkeys have been reported in Asia, the role of non-human primates (NHPs) in the JEV transmission cycle has not been intensively investigated. In this study, we demonstrated neutralizing antibodies against JEV in NHPs (Macaca fascicularis) and humans living in proximity in two provinces located in western and eastern Thailand by using Plaque Reduction Neutralization Test (PRNT). We found a 14.7% and 5.6% seropositive rate in monkeys and 43.7% and 45.2% seropositive rate in humans living in west and east Thailand, respectively. This study observed a higher seropositivity rate in the older age group in humans. The presence of JEV neutralizing antibodies in NHPs that live in proximity to humans shows the occurrence of natural JEV infection, suggesting the endemic transmission of this virus in NHPs. According to the One Health concept, regular serological studies should be conducted especially at the animal-human interface.

Seroprevalence of Chikungunya and Zika virus in nonhuman primates: A systematic review and meta-analysis.

Chikungunya virus (CHIKV) and Zika virus (ZIKV) are mosquito-borne viruses that have caused several outbreaks worldwide. Aedes mosquitoes transmit these viruses mainly through sylvatic and urban transmission cycles. In the sylvatic cycle, nonhuman primates (NHPs) can be infected with CHIKV and ZIKV and may play an essential role as reservoirs for virus transmission. To improve our knowledge on the role of NHPs in the sylvatic cycle, we performed a systematic review and meta-analysis study on the seroprevalence of CHIKV and ZIKV worldwide in NHPs. According to the PRISMA guidelines, 17 CHIKV and 16 ZIKV seroprevalence studies in NHPs from 3 online databases: PubMed, Embase, and Scopus were selected. Data were extracted, including location and study year, type of NHP, sample size, serological tests, and seropositivity. All included studies have high-quality scores, between 5 and 8, corresponding to the grading criteria. Seroprevalence estimation was pooled using the 'meta' package in the R statistical software. The estimated pooled seroprevalence of CHIKV and ZIKV in NHP was 17% (95%CI: 5-34, I2: 99%, p < 0.05) and 6% (95% CI: 2-12, I 2 : 92%, p < 0.05), respectively. Most of the NHPs tested were wild Old World monkeys. The subgroup was analyzed by continents; high seropositive CHIKV and ZIKV were found in African NHPs at 35% (95% CI 9-66.0, I 2  = 100) and 16% (95% CI 1-44, I 2  = 97), respectively. While NHPs in America have 7% (95% CI 0-28, I 2 = 99) and 2% (95% CI 1-3, I 2 = 54) against CHIKV and ZIKV. In Asia, 6% (95% CI: 5-34, I 2  = 96) CHIKV seroprevalence and 7% (95% CI 0-20, I 2  = 98) ZIKV seroprevalence were found in NHP. This study provides a comprehensive overview of the seroprevalence of CHIKV and ZIKV among NHPs in various regions.

Virological, Serological and Clinical Analysis of Chikungunya Virus Infection in Thai Patients.

From 2018 to 2020, the Chikungunya virus (CHIKV) outbreak re-emerged in Thailand with a record of more than 10,000 cases up until the end of 2020. Here, we studied acute CHIKV-infected patients who had presented to the Bangkok Hospital for Tropical Diseases from 2019 to 2020 by assessing the relationship between viral load, clinical features, and serological profile. The results from our study showed that viral load was significantly high in patients with fever, headache, and arthritis. We also determined the neutralizing antibody titer in response to the viral load in patients, and our data support the evidence that an effective neutralizing antibody response against the virus is important for control of the viral load. Moreover, the phylogenetic analysis revealed that the CHIKV strains we studied belonged to the East, Central, and Southern African (ECSA) genotype, of the Indian ocean lineage (IOL), and possessed E1-K211E and E1-I317V mutations. Thus, this study provides insight for a better understanding of CHIKV pathogenesis in acute infection, along with the genomic diversity of the current CHIKV strains circulating in Thailand.

Seroprevalence of Dengue, Zika, and Chikungunya Viruses in Wild Monkeys in Thailand.

Zoonotic pathogens such as arboviruses have comprised a significant proportion of emerging infectious diseases in humans. The role of wildlife species as reservoirs for arboviruses is poorly understood, especially in endemic areas such as Southeast Asia. This study aims to determine the exposure history of different macaque species from national parks in Thailand to mosquito-borne flaviviruses and alphavirus by testing the serum samples collected from 25 northern pigtailed macaques, 33 stump-tailed macaques, and 4 long-tailed macaques for the presence of antibodies against dengue, Zika, and chikungunya viruses by plaque reduction neutralization assay. Specific neutralizing antibodies against Dengue virus (DENV1-4) and Zika virus (ZIKV) were mainly found in stump-tailed macaques, whereas neutralizing antibody titers were not detected in long-tailed macaques and pigtailed macaques as determined by 90% plaque reduction neutralization assay (PRNT90). One long-tailed macaque captured from the south of Thailand exhibited antibody titers against chikungunya virus (CHIKV), suggesting enzootic of this virus to nonhuman primates (NHPs) in Thailand. Encroachment of human settlements into the forest has increased the interface that exposes humans to zoonotic pathogens such as arboviruses found in monkeys. Nonhuman primates living in different regions of Thailand showed different patterns of arboviral infections. The presence of neutralizing antibodies among wild monkeys in Thailand strongly suggests the existence of sylvatic cycles for DENV, ZIKV, and CHIKV in Thailand. The transmission of dengue, Zika, and chikungunya viruses among wild macaques may have important public health implications.

Functional and structural analysis of trehalose-6-phosphate phosphatase from Burkholderia pseudomallei: Insights into the catalytic mechanism.

We report the functional and structural characterization of trehalose-6-phosphate phosphatase (TPP), from the Gram-negative bacterium B. pseudomallei that causes melioidosis, a severe infectious disease endemic in Southeast Asia and Northern Australia. TPP is a key enzyme in the trehalose biosynthesis pathway, which plays an important role in bacterial stress responses. Due to the absence of this biosynthetic pathway in mammals, TPP has drawn attention as a potential drug target, to combat antibiotic resistance. In this context, we present a detailed biochemical analysis of purified recombinant TPP, reporting its specific high catalytic activity toward the trehalose-6-phosphate substrate, and an absolute requirement for its Mg2+ cofactor. Furthermore, we present the crystal structure of TPP solved at 1.74 Å, revealing the canonical haloacid dehalogenase (HAD) superfamily fold and conserved substrate binding pocket, from which insights into the catalytic mechanism may be deduced. Our data represent a starting point for the rational design of antibacterial drugs.