Several lines of evidence suggest that pigs act as a reservoir of hepatitis E virus (HEV). This dissertation presents data from studies conducted from August 2010 – August 2011 in Nan, Thailand. These studies define the previously unknown burden of HEV in pig and human populations in Nan province, and evaluate the transmission of HEV among humans having direct or indirect contact with the reservoir in pig. This work begins with a literature review. The first study addressed the risks for HEV transmission between pigs in different sized farms, and possible risk factors among pigs in a cross-sectional study. This study found a 9.9% (87/879) seroprevalence of anti-HEV among pigs and 2.9% of pigs had HEV ribonucleic acid (RNA) positive fecal samples. All HEV sequences corresponded to genotype 3. Pigs raised on medium sized farms with 30-300 pigs per farm had higher anti-HEV seroprevalence than pigs raised on larger farms with over 300 pigs after controlling for other potential confounders. Better hygienic practices were used in larger farms compared with small or medium sized farms. The second study addressed the association between occupational pig exposure to HEV infection among farmers over the age of 15 and the general population without direct contact with pigs in a cross-sectional study. The overall prevalence of anti-HEV was 23.0% (118/513). There was no association between anti-HEV prevalence and direct exposure to pigs. Frequent consumption of organ meat ≥ 2 times per week was a significant risk factor for HEV seroprevalence, adjusted odds ratio (OR) 3.23, 95% confidence interval (CI) 1.15, 9.01. Serum samples from all subjects with recent symptoms compatible with hepatitis who were IgM anti-HEV positive among the farmers and 40 serum samples from the control unexposed group with the highest mean optical density (OD) value were evaluated for HEV RNA by reverse transcriptase polymerase chain reaction (RT PCR). None of the samples were HEV RNA positive. These studies establish that HEV is endemic among pig populations in Nan province. It appears that HEV infections in humans are acquired more frequently as a food-borne infection than by direct contact with pigs in this population.
|Advisor:||Nelson, Kenrad E.|
|School:||The Johns Hopkins University|
|School Location:||United States -- Maryland|
|Source:||DAI-B 75/06(E), Dissertation Abstracts International|
|Subjects:||Occupational health, Epidemiology, Veterinary services|
|Keywords:||Cross sectional study, Genotype 3, Hepatitis E virus, Occupational exposure, Pig, Thailand|
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