Epidemiology of Hepatitis E Virus (HEV) strains identified in Italian pigs affected by different pathological conditions

Hepatitis E (HE) is an infectious viral disease that in humans shows clinical and morphological features of acute hepatitis. The aetiological agent is the hepatitis E virus (HEV). HE represents an important public health problem in developing countries where it is frequently epidemic and is primarily transmitted by the faecal-oral route. In recent years, a number of sporadic cases have also been described in industrialised countries, Italy included. Increasing evidence supports the hypothesis that HE is an emerging zoonotic disease, and that pigs are the main animal reservoir of the infection. Swine HEV was first identified in 1997 in USA and is now considered to be widespread in pig herds all over the world. In general HEV in pigs seems to be subclinical, although some studies have shown a possible correlation of the infection with liver damage. Moreover, its possible interaction with other pig pathogens such as PCV2 and PRRSV is still to be fully clarified. The aims of this study were: the assessment of HEV prevalence in Italian pigs affected by different pathological conditions, the evaluation of possible risk factors related to the infection and the evaluation of possible interactions of HEV with other concomitant pig pathogens. 137 randomly selected pigs of 2-4 months of age, from 45 Italian herds, received by the IZSLER for diagnostic purpose were enrolled in the study. For each pig, information regarding age, farm of origin and presence of pathological conditions or coinfections detected at necropsy or after laboratory analyses were collected. For detection of HEV RNA, bile samples were collected from each pig and examined by nested-RT-PCR using two sets of degenerate primers. Positive samples were confirmed to be HEV by sequence analysis. A binary logistic regression was performed to evaluate the HEV prevalence in function of possible risk factors such as age of the animals, herd type, presence of pathological conditions detected at necropsy or concomitant infection with PCV2 or PRRSV. 41 of the 137 examined pigs (29.9%) tested positive for HEV RNA with at least one of the set of primers used. No statistically significant correlations between HEV positivity and herd typology or concomitant pathological conditions or coinfections were detected. However, the HEV positivity was significantly higher (46.9%, OR=3.78; p=0.009) in animals between 80-120 days of age than in pigs <80 days of age (20%). This study confirms that HEV infection is widespread in Italian pigs. The higher positivity in pigs of 80-120 days of age is in agreement with other studies and can be probably correlated to the decreasing of the maternal immunity in this category of animals. The observation that HEV positivity is apparently not related with any pathological condition seems to confirm the sub-clinical nature of HEV infection in swine. Although in this study a clear correlation with concomitant infections sustained by PCV2 or PRRSV has not been demonstrated, further studies will be necessary to fully understand the role of HEV in these and other multifactorial or conditioned diseases.