Hepatitis E is a viral liver disease of humans which can be carried by pigs and other animals. Recent studies have shown a rise in the prevalence of Hepatitis E on a global scale but this may be, in part, due to increasing interest in viral surveillance.
Hepatitis E (HEV) virus comprises four genotypes (G1-4), each with a different geographical distribution and host range. While G1 and G2 infect humans only, G3 and G4 are contagious to humans from animals actively infected with the virus (viraemic animals). Studies have demonstrated a potential link between pigs and human cases of HEV but this is considered to be of low risk to human health. A UK national zoonosis study in 2013 demonstrated that only 1% (n=6) of the total pigs sampled in the survey (n=600) displayed any signs of clinical viraemia relating to hepatitis E.
Of the 676 cases of human infection by hepatitis E reported by Public Health England, two thirds were of a virus type not indigenous to England and Wales. Sequencing work revealed that about 70% of G3 human infections are linked to a subgroup of viruses which are not found in pigs in the UK.
Risks factors for Hepatitis E
The risk levels for contracting Hepatitis E from pigs are extremely low, but higher in people who are immunocompromised or pregnant. Infection is generally through faeces or infected meat which is raw or undercooked.
Zoonotic viral infection in developed countries is mainly associated with direct contact with viraemic animals, such as pigs whereas, in developing countries, it is the faecal contamination of water supplies which acts as the major route of human infection. The mortality rate from contracting the virus is low (around 1%) but this can be higher in pregnant (up to 25%) and immunosuppressed individuals.
The UK pig industry has implemented a number of controls to reduce the risk of spread of zoonotic agents and cross contamination. At farm level this includes strong biosecurity, cleaning and disinfection of sheds. All livestock lorries are required to be cleaned and disinfected post loading. At the slaughterhouse, that includes strong lairage management practice such as no mixing of batches, no build-up of faeces and regular cleaning. This is combined with high hygiene practices during slaughter.
Cooking to reduce the risk of Hepatitis E
Current recommendations are to cook pork and products containing pork to a minimum temperature of 75oC at the centre of the thickest part. This is considered sufficient to protect consumers from hepatitis E virus and other pathogenic micro-organisms.
Normal grilling or frying of sausages until they are well browned and firm inside, with no traces of pink meat, usually results in centre temperatures in excess of 85oC. However, it is not recommended to rely on visual cues alone for determining thorough cooking and it is better to use a meat thermometer to check the temperature of cooked meat and meat products before consuming them.
In addition, effective hand washing and hygiene precautions in the kitchen are essential to prevent foodborne illness through handling of raw meat or cross contamination of cooked food by raw food.