BIOSECURITY MEASURES TO REDUCE HEPATITIS E VIRUS TRANSMISSION WITHIN PIG FARMS
Summary
Hepatitis E virus (HEV) can infect humans and cause inflammation of the liver. For people living in industrialized countries, pigs are the main source of human infection. Pigs that become infected do not fall ill, but they do shed HEV in their feces, and the virus can reside in their liver. Therefore, transmission of HEV from pigs to humans may occur via contact with pig manure or consumption of raw or undercooked pork liver.
HEV is present in most pig farms, and it is currently not known how to stop infection in pigs, to indirectly protect humans against HEV. Thus, we aimed to find out what measures pig farmers can take, to prevent pigs on their farm from becoming infected.
In the present study, 73 farms of two classes were compared; 1: farms on which every group of pigs becomes infected with HEV, 2: farms in which some groups of pigs remain free from HEV. Measures that are taken more often in one of the two farm classes, may protect against HEV infection, or the other way around, may increase the chance of HEV infection. Farms were classified based on blood samples collected from several groups of pigs from those farms at slaughter. The measures taken by farmers were identified by conducting a questionnaire and an audit on the farms. For both the questionnaire and audit, emphasis was put on measures regarding internal biosecurity, which entails all things a farmer can do to stop spread of a virus within the farm, like cleaning an empty barn, rodent control and changing or cleaning boots between groups of pigs.
In the statistical analysis, the answers to all questions and all checkpoints in the audit were taken into account and a model was used to distinguish the measures that had the strongest relationship with having a group of pigs that remained free from HEV.
We have found that the floor material present in barns with fattening pigs have the strongest relationship with an HEV free group of pigs. Namely, rubber flooring increased the odds of having an HEV free group by 6 fold, and steel by 7 fold. We hypothesize that rubber and steel can be cleaned more effectively than the common floor material concrete, so that rubber and steel floors indirectly prevent new pigs in the barn from becoming infected. Furthermore, cleaning driving boards, that are used to move pigs from one barn to another, protects against HEV infection of pigs. Possibly, the driving boards are a source of transmission between pigs. Also, controlling flies is a protective measure, especially when done by releasing predatory flies that eat the eggs of barn flies. A farm characteristic that may increase the chance of HEV infection is a long duration of the fattening period, which may be the result of pigs becoming older on those farms and thereby increasing the time in which they are at risk of becoming infected.
In conclusion, several measures related to cleaning and cleanability of pig farms can be taken, as well as improving control of flies, to prevent groups of pigs from becoming infected by hepatitis E virus.