Prevalence of poliovirus vaccine strains in randomized stool samples from 2010 to 2018: encompassing transition from the trivalent to bivalent oral poliovirus vaccine.

Global eradication of poliovirus (PV) has previously relied on the live attenuated oral poliovirus vaccine (OPV). However, in order to eliminate the risk of vaccine-associated paralytic poliomyelitis, the use of OPV will soon be discontinued. Thailand has introduced inactivated polio vaccine since December 2015 and replaced trivalent with bivalent OPV since April 2016. To provide crucial surveillance data during this polio vaccine transition period, poliovirus shedding in stool was performed. A total of 7446 stool samples between 2010 and September 2018 were tested for poliovirus using reverse-transcription polymerase chain reaction. Approximately 0.44% (33/7446) of the samples tested were positive for PV. All positive specimens had more than 99% homology with the Sabin vaccine strain, based on complete VP1 nucleotide sequences. Although trivalent OPV use has been discontinued in Thailand since April 2016, PV type 2 could be detected in stool samples collected in May 2016 but has not been found afterwards. The use of bivalent OPV was able to reduce PV type 2 shedding in stools and could contribute to the reduction of vaccine-associated paralytic poliomyelitis in Thai children.

Analysis of the spike, ORF3, and nucleocapsid genes of porcine epidemic diarrhea virus circulating on Thai swine farms, 2011-2016.

Porcine epidemic diarrhea virus (PEDV) outbreaks on pig farms have caused significant economic loss in the swine industry since it was first reported in Thailand a decade ago. Anecdotal evidence suggests that PEDV is now endemic in this region, therefore genome information of circulating PEDV is important for molecular surveillance and evaluation of potential benefits of field vaccination. Here, we characterized PEDV infection on commercial Thai swine farms by screening 769 samples of feces and small intestinal contents from pigs with diarrhea between 2011 and 2016. Using reverse-transcription polymerase chain reaction targeting the spike (S) gene, 153 PEDV-positive samples were further subjected to analysis of the open reading frame 3 and nucleocapsid (N) genes. Comparison of 95 samples in which nucleotide sequencing was successfully obtained for all three genes revealed evolutionary diversity among the Thai PEDV strains. Phylogenetic analyses suggest that although some Thai strains changed little from years past, others resembled more closely to the recent strains reported in China. Interestingly, eight Thai PEDV strains possessed amino acid deletions in the N protein. The PEDV sequence divergence may be responsible for driving periodic outbreaks and continued persistence of PEDV on commercial swine farms. Our findings provide important insight into regional PEDV strains in circulation, which may assist future inclusions of suitable strains for future PEDV vaccines.

Hepatitis E virus infection in Thai blood donors.

BACKGROUND: Hepatitis E virus (HEV) infection in several industrialized and developing countries is associated with the consumption of pork and other meat products, an exposure risk among the majority of blood donors. We aimed to evaluate the prevalence of HEV in plasma from healthy blood donors in Thailand. STUDY DESIGN AND METHODS: We screened blood samples collected between October and December 2015, from 30,115 individual blood donors in 5020 pools of six, for HEV RNA using in-house real-time reverse-transcription polymerase chain reaction (RT-PCR). Thrice-reactive samples were subjected to a commercial real-time RT-PCR (cobas HEV test) and evaluated for anti-HEV immunoglobulin M and immunoglobulin G antibodies. Genotyping using nested RT-PCR, nucleotide sequencing, and phylogenetic analysis was performed. RESULTS: Twenty-six donors were positive for HEV RNA by the in-house assay, nine of whom were also positive by cobas test. None of the latter were reactive for anti-HEV immunoglobulin M or immunoglobulin G antibodies. Six samples were successfully genotyped and found to be HEV genotype 3. Thus, the frequency of HEV infection among healthy Thai blood donors is 1 in 1158. CONCLUSION: The presence of HEV RNA in the Thai blood supply was comparable to the rates reported in western European countries, but higher than in North America and Australia.

Porcine rotavirus C in pigs with gastroenteritis on Thai swine farms, 2011-2016.

Swine are economically important food animals, but highly contagious porcine epidemic diarrhea virus (PEDV) and rotavirus can afflict pig herds and contribute significantly to piglet morbidity and mortality. While there have been studies on rotavirus group A (RVA) in Thailand, reports of rotavirus group C (RVC) are limited. Here, we aimed to identify the prevalence of RVC circulating on Thai commercial swine farms. We analyzed 769 feces and intestine mucosal contents of pigs affected with diarrhea between 2011 and 2016 using RT-PCR specific for the PEDV spike (S), rotavirus glycoprotein (G) VP7, and protease-sensitive protein (P) VP4 genes. We found that 6.6% (51/769) of samples tested positive for RVC, of which 11 samples were co-infected with RVA and four samples were co-infected with PEDV. Three samples tested positive for all three viruses. Phylogenetic analysis of the VP7 gene showed that the most frequent RVC genotype was G1, which grouped with the prototypic RVC Cowden strain. While G6 and G9 were also common, G3 was relatively rare. Analysis of the VP4 gene revealed that the most common P type was P[5], followed by P[4], P[7], and P[1]. In all, there were six G/P combinations (G6P[5], G1P[1], G1P[4], G1P[5], G9P[4], and G9P[7]), of which G6P[5] was the most predominant.

Human enteroviruses associated with and without diarrhea in Thailand between 2010 and 2016.

Non-bacterial acute gastroenteritis (AGE) associated with virus infection affects individuals living in developing countries, especially children. To investigate whether shedding of certain human enterovirus (EV) is more frequently detected in the stool of individuals with AGE of unknown etiology than individuals without AGE symptoms, we tested fecal samples collected from 2,692 individuals with diarrhea between January 2010 and December 2016. Samples were tested for rotavirus, norovirus, and EV by reverse-transcription polymerase chain reaction (RT-PCR) and adenovirus by PCR. EV-positive samples were subjected to sequencing and phylogenetic analysis to identify EV species and types. Findings were compared to EV found in 1,310 fecal samples from individuals without AGE who were diagnosed with hand, foot, and mouth disease (HFMD). While the majority of viruses identified in AGE consisted of human rotavirus (22.7%), norovirus (11.4%) and adenovirus (9.3%), we identified EV (6.2%) belonging mainly to species B, C, and rhinovirus. In contrast, >92% of EV found without AGE symptoms belonged to species A. Although AGE symptoms are not often attributed to EV infection, EV was associated with diarrhea of unknown etiology at least in 3.4% of AGE cases. While CV-A6 was most likely to be found in stools of HFMD patients, rhinovirus A and C were the two most common EV species associated with AGE. Elucidating group-specific EV infection in diseases with and without AGE will be useful in assisting identification, clinical management, and the surveillance of EV infection in the community.

Hepatitis E Virus in Pork and Variety Meats Sold in Fresh Markets.

Swine is an economically important livestock, yet pork consumption and close contact with pigs are associated with the risk of hepatitis E virus (HEV) infection. Limited data on the prevalence of HEV in Southeast Asia have mainly examined farm animals. To investigate the potential zoonotic transmission of HEV from dietary consumption of pork and variety meats (i.e., offal or organ meats), we obtained 1090 liver, 559 pork meat, and 556 intestine samples from fresh markets in the Bangkok metropolitan area between November 2014 and February 2015. The presence of HEV was assessed using reverse-transcription polymerase chain reaction. Concurrently, 720 bile and 553 fecal samples from a slaughterhouse were also examined. Overall, HEV RNA was found in 0.23 % of the market samples and 3.93 % of the slaughterhouse samples. Fecal and bile samples were more likely to test positive compared to liver, pork, and intestine samples (p < 0.001). Phylogenetic analysis showed that all HEV sequences obtained in this study formed a cluster closely related to genotype 3f. Pork and variety meats derived from pigs are commonly sold in fresh markets throughout Southeast Asia. Here, a relatively low HEV prevalence from pork and variety meats sold in Bangkok was found. Additional studies will be required to further assess potential dietary transmission of HEV elsewhere in the region.