Abstract
Hepatitis E virus (HEV) is a zoonotic pathogen with consumption of pork and derived products identified in different countries as a risk factor for human exposure to HEV. Great efforts have been made to understand the dynamics of virus transmission within domestic swine populations through modelling. However, from a food safety prospective, it is critical to integrate the parameters involved in the transmission dynamics with those governing the actual presence of HEV in the bloodstream, the liver, gallbladder or faeces. To date, several aspects related to the pathogenesis of the disease are still unknown or characterized by significant levels of uncertainty, making this conjunction challenging. We used published serological data obtained from pigs in a farrow-to-finish farm to implement an Immune-Susceptible-Infected-Recovered (MSIR) model reproducing the on-farm dynamics that lead to the occurrence of viraemic pigs at slaughter. Expert opinion on the length of time infectious HEV can be detected in liver, gallbladder/bile and faeces after recovery from viraemic status were used to inform a stochastic model aimed at estimating the expected proportion of viraemic pigs, pigs with infectious HEV in liver, gallbladder/bile and faeces entering the slaughterhouse. To simulate the potential effect of on-farm mitigation strategies, we estimated the changes in outcomes of interest as a function of variations in the baseline transmission parameters. The model predicted a proportion of viraemic pigs entering the slaughterhouse of 13.8% while the proportions of, and ranged from 13.8% to 94.4%, 13.8% to 94.7% and from 25.3% to 30.8% respectively, due to the uncertainty surrounding the experts’ opinions. Variations in MSIR model’s parameters alert of the need to carefully consider the application of mitigation strategies aimed at delaying the decay of maternal immunity or the peak of the within herd transmission. When the rate of decay of maternal immunity and the transmission rate were decreased between 80% and 5% and 40% and 5% from the baseline values respectively, adverse effects on were observed. The model highlights the relevance of specific aspects in the pathogenesis of the disease from a food safety prospective and it was developed to be easily reproducible and updatable as soon as accurate data becomes available. As presented, the model can be directly connected to existing or future pig-related models to estimate the significance of the identified parameters on the risk of human exposure to HEV through consumption of pork products.
Highlights
12 A high seroprevalence of zoonotic Hepatitis E virus (HEV) is reported in pig populations of industrialized countries [8,9,10,11,12] and HEV RNA has been isolated from processed pork products, especially those containing liver [13,14,15]
Our model predicted a proportion of 13.8% viraemic pigs at depopulation, which is consistent with the proportion observed by De Deus et al [29] (i.e. 12.5%)
When β was kept to its baseline value, a reduction in δ equal to a value between 0.05% and 80.0% of its baseline value led to an increased proportion of viraemic pigs entering the slaughterhouse
Summary
12 A high seroprevalence of zoonotic HEV is reported in pig populations of industrialized countries [8,9,10,11,12] and HEV RNA has been isolated from processed pork products, especially those containing liver [13,14,15]. A recent case-control study associated the consumption of processed pork products with indigenous HEV infection [16] in England and Wales and several studies indicated meat products as a source of infection in humans [17,18,19] This evidence and the ubiquitous nature of the virus in animals - in domestic pigs- raises public health concern for zoonotic infection through direct contact with infected animals or through the consumption of animal meats. Two quantitative risk assessment (QRA) have been published, both aimed at estimating the probability of human exposure to HEV through consumption of pork liver and liver sausages in Switzerland [20, 21] These models considered the food products rather than individual pigs as the starting point, the farm level dynamics describing the infectious status of the animals entering the slaughterhouse and the events occurring at processing stage were not explored
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
