Pigs carry hepatitis E virus (HEV), which they can pass on to humans. But now research from Japan published in Online Open Access journal BMC Veterinary Research says that pigs get HEV early enough to minimise the risk of human infection. The scenario humans need to worry about would occur if the infection rate in pigs drops. At low infection rates, there is actually a higher chance pigs will pass on HEV to humans at slaughter.

Kunio Satou and Hiroshi Nishiura analysed blood test data from 2,500 pigs, natural hosts for the virus, on Japanese farms at Hokkaido, Honshu and Kyushu. They found that by the age of 150 days, over 95% of pigs had been infected with HEV.

Inoculation studies have shown that the virus remains in pigs faeces and some organs for up to 30 days after infection. This means that the chances of pigs excreting the virus when they are slaughtered at the age of 180 days are currently small. However, if the infection weakens and pigs dont get infected with HEV until they are older, more pigs will still be carrying the virus when they reach the slaughterhouse.

HEV, which is found worldwide, can potentially cause acute hepatitis in humans. So monitoring infection rates could help protect meat processors and vets. The disease can be transmitted by drinking water contaminated with faeces as well as by eating pork: uncooked wild boar liver is one Japanese delicacy that frequently leads to infection.

Suckling pigs don't contract the virus in their first 30 days, because a maternal antibody protects them. Vaccines are currently under development against HEV, although Satou and Nishiura suggest that changes in husbandry practices and avoiding eating raw liver might be more cost-effective measures should HEVs hold on pig farms weaken.