Zoonotic Hepatitis E and Enteric Protozoa in Vietnam: Epidemiological Evidence from Animal Reservoirs to Human Health Risk

Abstract

This doctoral thesis explores the epidemiology of two underrecognized zoonotic pathogens: hepatitis E virus (HEV) and enteric protozoa (Entamoeba spp. and Cryptosporidium spp.) in Vietnam, a country with extensive pig farming and high risk of zoonotic spillovers. The research is structured in three chapters: HEV in Pigs and Wild Boars: The study analysed over 500 samples from domestic pigs and wild boars across Vietnam, revealing a high HEV RNA positivity: 25% in wild boars and 7% in pigs. Molecular characterization identified HEV-3a as the dominant subgenotype, with HEV-4b detected only in wild boars. These findings demonstrate pigs and wild boars as important HEV reservoirs, emphasizing the risk of zoonotic transmission through handling or consumption of pork and wild boar meat. HEV in Humans (Blood Donors and High-Risk Populations): Screening of 553 blood donors showed 27% anti-HEV IgG seropositivity but <1% anti-HEV IgM positivity and no HEV RNA detection, indicating widespread past exposure but low risk of transfusion-transmitted HEV. Among 745 patients with chronic hepatitis B or unexplained hepatitis, anti-HEV IgG rates were similar or higher, especially in patients with cirrhosis or liver cancer. However, HEV exposure correlated strongly with age and gender, suggesting no direct role in liver disease progression. The data confirm high endemicity but low current HEV transmission risk. Entamoeba and Cryptosporidium in Pigs and Wild Boars: The thesis found a high prevalence of Entamoeba spp. (62%) and Cryptosporidium spp. (31%) in pigs and wild boars. Species identified included Entamoeba suis, E. polecki (subtypes ST1 and ST3), E. hartmanni, Cryptosporidium scrofarum, and C. suis. Notably, E. hartmanni was detected in Vietnamese pigs for the first time. Several of these species have documented zoonotic potential, highlighting a possible risk of cross-species transmission to humans. Taken together, the research thesis provides important data on zoonotic HEV and protozoan parasites in animal reservoirs and highlights the need for increased surveillance and One Health approaches to mitigate zoonotic risks. Despite widespread HEV exposure, there is no evidence of transmission through transfusions or of HEV as a common cause of unexplained hepatitis in Vietnam. The considerable diversity and prevalence of Entamoeba and Cryptosporidium in pigs and wild boars requires further investigation of their zoonotic potential and public health implications.