Molecular and serological investigation of Hepatitis E virus in pigs slaughtered in Northwestern Italy

Abstract

Background Hepatitis E Virus (HEV) is recently considered an emerging public health concern. HEV genotypes 1 and 2 are widely distributed and pathogenic only for humans. In contrast, HEV, genotypes 3 and 4 are observed in swine, deer, wild boars and rabbits and can also be transmitted to humans. The presence of HEV in the liver, muscle, faeces, blood, and bile was detected by real-time RT-PCR in 156 pigs belonging to twenty different farms, ranging from 1 to 8 months of age. The phylogenetic analysis was performed on the viral strain present in the positive biological matrix, with the lowest Ct. HEV-IgG and HEV-IgM in the sera were analysed by two different ELISA kits. Results Twenty-one pigs, i.e., 13.46% of them (21/156, 95% CI: 8.53%-19.84%), tested positive for HEV in at least one biological matrix by real-time RT-PCR, while phylogenetic analysis revealed the presence of HEV subtypes 3f and 3c. Pig serums analysed by ELISA showed an overall prevalence of 26.92% (42/156, 95% CI: 20.14%-34.60%) for HEV-IgG, whereas the 28.95% (33/114, 95% CI: 20.84%-38.19%) of them tested negative resulted positive for the HEV-IgM. Conclusions The faeces are the biological matrix with the highest probability of detecting HEV. The best concordance value (Kappa Kohen index) and the highest positive correlation (Phi index) were observed for the correlation between bile and liver, even when the number of positive liver samples was lower than the positive bile samples. This finding may suggest that a higher probability of HEV occurs in the bile, when the virus is present in the liver, during the stages of infection. Finally, the presence of HEV in muscle was observed in 11 pigs, usually used for the preparation of some dishes, typical of the Italian tradition, based on raw or undercooked meat. Therefore, their consumption is a possible source of infection for final consumer.

Hepatitis E Virus (HEV) in Heavy Pigs in Slaughterhouses of Northern Italy: Investigation of Seroprevalence, Viraemia, and Faecal Shedding

“…The absence of recent infection was further confirmed by the limited presence of IgM (5 out of 260 pigs, 1.9%). This percentage is lower than those observed in previous studies (ranging from 29.0% to 47.3%) conducted in younger animals [ 20 , 26 , 27 ].…”

“…For instance, in the UK, 15.0% of caecal contents tested positive in slaughtered pigs at the age of <12 months [ 20 ], while 25.6% of caecal contents were positive in pigs (5–6 months) in the Netherlands [ 17 ]. The differences observed may primarily be associated with age, as higher prevalence is often observed in faeces from younger animals [ 26 ]. However, significant variations could also be attributed to factors at farm level such as biosecurity measures, management system, and feed.…”

“…However, several studies have reported viraemia in pigs at slaughterhouses, with percentages ranging between 5.7% and 14.3% in England, the USA, and Italy [ 12 , 20 , 26 , 49 ], and 36.2% in the Netherlands and 44.4% in Scotland [ 17 , 27 ]. Except for the study conducted in the USA on animals older than 6 months, the studies investigated younger pigs.…”

“…The earlier age of slaughtering is considered a risk factor that increases the number of animals still being positive for HEV presence in the liver [ 25 ]. Information on viraemia is limited, with only a few studies reporting the presence of HEV RNA in pig blood at slaughterhouses, primarily in young pigs [ 12 , 17 , 20 , 26 , 27 ]. Viraemia and the presence of IgM are frequently associated [ 20 ], and the presence of IgG does not exclude the presence of IgM, indicating the existence of a complex dynamic of infection that can vary considerably.…”

“…However, it is also prevalent in small farms, which are more common in the south of the country, with farm prevalence ranging from 12.5% to 50% [ 30 , 31 ]. At slaughterhouses, the virus has been detected in various tissues, including the liver, faeces, bile, and rarely in blood [ 12 , 26 , 32 ]. Moreover, in Italy, HEV has been identified in other wild, synanthropic, or domestic species, including wild boars [ 33 , 34 ], wolves [ 35 ], red deer [ 36 ], rats [ 37 ], goats [ 38 ], and sheep [ 39 ].…”