Center for Animal & Veterinary Sciences, Professional and Scientific Services, Animal and Veterinary Service, National Parks Board (NParks), Singapore, Singapore.
Singapore Food Agency (SFA), Singapore, Singapore.
Transbound Emerg Dis. 2022 Mar;69(2):286-296. doi: 10.1111/tbed.13977. Epub 2021 Jan 29.
Hepatitis E is a significant liver disease caused by infection with hepatitis E virus (HEV). The risk factors for hepatitis E in developed countries include blood transfusion and ingestion of undercooked meat or meat products derived from HEV-infected animals. Since 2000, there has been increased human hepatitis E incidence reported in Singapore. Although the causes of this increase have not been established, several studies have linked zoonotic HEV infections in humans to pork consumption. It is therefore important to closely monitor the presence of HEV in food sources for the prevalence and virulence. In this study, we demonstrated the presence of HEV in pigs imported into Singapore for consumption through serological and molecular investigation of live pig and post-slaughter samples collected between 2000 and 2019. Among imported pigs, anti-HEV antibody prevalence remained at a level around 35% until 2017, with a statistically significant increase in 2018. HEV RNA was detected in 8.40% (34/405) of the faecal samples, indicative of an active infection in the pigs. HEV RNA was also detected in 6.67% (4/60) of liver samples obtained post-slaughter. We also report the development of an RT-PCR-based next-generation sequencing (NGS) method that enabled full sequencing of the HEV genome in HEV RNA-positive samples in a relatively short span of time. Phylogenetic analysis identified the HEV in one of the imported pigs (HEV-S28) as genotype 3a, which clustered together with the human HEV strains previously identified in Singapore. We found that the HEV-S28 strain exhibited amino acid substitutions that are associated with reduced HEV replication efficiency. The increase in anti-HEV seroprevalence in the pig population from 2018 is worth further exploration. We will continue to monitor the prevalent HEV strains and assess the genetic diversity of HEV in the imported pigs to confirm the potential association with human infections.
戊型肝炎是一种由戊型肝炎病毒（HEV）感染引起的重要肝脏疾病。发达国家的戊型肝炎的危险因素包括输血和摄入未煮熟的来自 HEV 感染动物的肉或肉类产品。自 2000 年以来，新加坡报告的人类戊型肝炎发病率有所增加。尽管尚未确定这种增加的原因，但有几项研究将人类的动物源性 HEV 感染与猪肉消费联系起来。因此，密切监测食品中 HEV 的存在对于流行率和毒力非常重要。在这项研究中，我们通过对 2000 年至 2019 年期间收集的活猪和屠宰后样本进行血清学和分子调查，证明了进口到新加坡供消费的猪中存在 HEV。在进口猪中，抗-HEV 抗体的流行率一直保持在 35%左右，直到 2018 年才出现统计学上的显著增加。在 8.40%（34/405）的粪便样本中检测到 HEV RNA，表明猪中存在活跃感染。在屠宰后获得的 6.67%（4/60）的肝样本中也检测到 HEV RNA。我们还报告了一种基于 RT-PCR 的下一代测序（NGS）方法的开发，该方法能够在相对较短的时间内对 HEV RNA 阳性样本进行 HEV 基因组的全序列分析。系统进化分析表明，其中一头进口猪（HEV-S28）中的 HEV 为 3a 基因型，与之前在新加坡鉴定的人类 HEV 株聚类在一起。我们发现，HEV-S28 株表现出与降低 HEV 复制效率相关的氨基酸替换。自 2018 年以来，猪群中抗-HEV 血清阳性率的增加值得进一步探讨。我们将继续监测流行的 HEV 株，并评估进口猪中 HEV 的遗传多样性，以确认与人类感染的潜在关联。
