When cooking pork products it is crucial you cook them enough to get rid of any signs of pink. George F Winter explains how you can run the risk of contracting the hepatitis E virus
Many people are familiar with hepatitis viruses A, B and C; but hepatitis E – officially named as such in 1990 - is relatively unknown. For example, a report in the British Medical Journal (12 November, 2014) quoted hepatitis E expert and consultant gastroenterologist at the Royal Cornwall Hospital Trust Dr Harry Dalton as saying that of 122 cases of acute hepatitis E infection he had treated, not a single patient had ever heard of it before diagnosis.
HEV is widespread among pigs. For example, Irish researchers reported in the Irish Veterinary Journal last year that they had detected HEV antibodies in 27% of 330 pigs tested, concluding: ‘Hepatitis E virus is present in most Irish pig herds and in many animals within these herds.’ In the UK, the prevalence of HEV antibodies in pig herds is estimated at 85%.
According to the World Health Organisation, each year worldwide there are 20 million HEV infections; over 3 million acute cases of hepatitis E; and 57,000 hepatitis E-related deaths. In developing countries HEV infection is typically associated with large waterborne epidemics, due to poor sanitation and is usually transmitted by the faecal-oral route.
In recent years, however, evidence has shown that HEV infection occurs in developed countries, although compared to developing countries the modes of transmission have not all been established.
Evelyn Ring reported in the Irish Examiner (29 July 2014) that a study undertaken by the Irish Blood Transfusion Service showed that 5% of blood donors have been exposed to HEV. Dr Lelia Thornton, a Specialist in Public Health Medicine in the HSE Health Protection Surveillance Centre, told the paper: “In Ireland there have been 64 cases of HEV infection notified since 15 December 2015, when hepatitis E infection became a notifiable disease, and since January this year all blood donations in Ireland have been screened for evidence of HEV infection.”
Most people in developed countries do not develop symptoms following HEV infection, but when they do they occur more often in middle-aged and elderly men whose symptoms include jaundice, fever, nausea and abdominal pain.
HEV infection, however, can be a particular risk for pregnant women and those with pre-existing liver disease. Dr Thornton explained: “In some developing countries, pregnant women with hepatitis E, particularly those in the second or third trimester, are at an increased risk of acute liver failure, foetal loss and mortality. However, the high mortality associated with hepatitis E infection in pregnancy in developing countries is not seen in developed countries, perhaps due to differences in genotypes of the virus occurring in developed countries compared with developing countries.”
There are four strains, or genotypes, of HEV. Genotypes 1 and 2 occur in Asia and Africa; genotype 3 is found worldwide, including Europe and Ireland; and genotype 4 occurs in China and Japan.
Although a small proportion of those people exposed to HEV in Ireland could be attributed to travel or migration from regions where HEV is endemic, there seems to be an indigenous source of infection.
What could the source be? The title of a 2014 report published in the medical journal Epidemiology and Infection was unequivocal: “Hepatitis E virus in England and Wales: indigenous infection is associated with the consumption of processed pork products.”
In this study of 25 cases of HEV infection and 75 controls, researchers found that the consumption of pork pie, ham and sausages bought from a major UK supermarket chain was associated with HEV infection. The researchers also cited a study published in 2012 in the journal Emerging Infectious Diseases which showed that 10% of pork sausages sampled at point of sale from UK retailers contained detectable HEV ribonucleic acid, supporting pork sausages as a potential vehicle for HEV transmission.
There is further evidence implicating pigs as a major reservoir: a high prevalence of HEV antibodies in pigs; studies which have shown a high prevalence of HEV antibodies in pig handlers, abbatoir workers and vets caring for pigs; the genomes of HEV from pigs and humans are closely related; porcine HEV is transmissible to non-human primates; and human HEV can be transmitted to pigs.
In April 2010 the Irish Association of Pigmeat Processors published its 2020 Strategy – Irish Pigmeat Sector document, stating: “National output can continue to grow beyond 2015 and reach 5 million pigs by 2020.”
Considering the anticipated growth in Ireland’s pig industry, combined with the prevalence of HEV in its herds, what are the best steps to take to avoid the consumption of HEV-infected pork?
Dr Thornton said: “The best advice is to cook meat and meat products thoroughly, particularly pork products. Avoid raw or undercooked meat. And ensure that hands are washed carefully before preparing and eating food.”
The Food Safety Authority of Ireland (FSAI) recommends that pork and pork-containing products, such as sausages, should be cooked to a minimum temperature of 75C at the centre of the thickest part.
The FSAI also advises: “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 85C. 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.’ Yet the fact remains that many foodies prefer their cooked pork to be pink, perhaps encouraged by some chefs who are well-qualified in cookery, if not in microbiology.
For example, Jamie Oliver’s website offers this advice on cooking pork fillets: “Marinate or tenderise the fillet, then cook it quickly at a high temperature until slightly blushing pink in the middle for extra-juicy results. Cooking it for too long will dry the meat out …”
Such advice leaves Dr Harry Dalton unimpressed; he told me: “What doesn’t help is the trend of some celebrity chefs who suggest that pork tastes better when it’s undercooked and still pink in the middle. This is potentially very hazardous to human health.”
However, it’s worth noting that while the main reservoirs and sources of HEV infection in Europe are domestic pigs and wild boar, a recent review published last year in the journal Future Virology noted that several animal reservoirs have been described for HEV, including rats, deer, cows, sheep, goats, rabbits, dogs and cats. And the review cites shellfish as a further risk factor in HEV transmission. For example, HEV has been detected in commercial mussels sampled in Greece, Finland and Spain, and in 2009 there was a report of a hepatitis E food-borne outbreak on a cruise ship associated with shellfish consumption.
It seems clear that whatever the attractions of pink pork for the palate, it’s possible undercooked porcine delights may be a vehicle for HEV.
© Irish Examiner Ltd. All rights reserved