WHO and FAO look at Trichinella and Taenia saginata in meat

Experts have helped develop risk-based approaches to control two parasites in meat, requiring the re-evaluation of traditional practices and the assessment of regulatory and industry resources.

The Food and Agriculture Organization of the United Nations (FAO) and World Health Organization (WHO) publication covering Trichinella spp. and Taenia saginata recently posted details about the research work.

Trichinellosis is caused by consumption of raw or inadequately treated meat from domestic or game animals containing the larvae of parasites of the Trichinella species. A parasitic disease of cattle is caused by the larval stage of the human tapeworm Taenia saginata. Taeniosis occurs when people eat beef that has not been sufficiently heated or frozen to kill the parasite. Most cases involve a single tapeworm, which can persist for years.

Developing a risk-based control of Trichinella spp. and Taenia saginata in meat was started in October 2013 with an expert meeting in September 2014.

The report provides spreadsheet models to get quantitative information needed by public health officials when evaluating different post-mortem hygiene programs for Trichinella spp. and Taenia saginata in meat. These models enable development of risk scenarios to assess the effect of changes to digestion testing and meat inspection on the risk of human trichinellosis and taeniosis.

Trichinella and Taenia saginata
All genotypes of Trichinella are pathogenic for humans. A study published in 2011 found 65,818 confirmed trichinellosis cases and 42 deaths in 41 countries between 1986 and 2009.

In early infection, adult worms in the intestine can cause gastroenteritis, but the most severe symptoms are due to the migration and establishment of the larvae in muscle. These include swelling of the face or around the eyes, muscle pain, fever, conjunctivitis, and skin rash. Myocarditis, encephalitis and meningitis have been observed in severe cases. Symptoms diminish one to two months post-infection but chronic fatigue can persist. Most infected patients are not diagnosed until two or more weeks after exposure, when larvae have become established in the muscles.

Regulations for the inspection and control of the parasite exist in many countries. Treatment methods to inactivate Trichinella larvae in meat include cooking and irradiation, and freezing for some genotypes.

Taenia saginata is most prevalent in sub-Saharan Africa, Latin America, Asia, and some Mediterranean countries. Tens of millions of people are likely infected worldwide, but reliable estimates are lacking because of the low pathogenicity and under-reporting, researchers reported.

For many otherwise healthy people, symptoms are mild and unrecognized for years until the parasite dies or is eliminated. The most common manifestation is mild gastrointestinal illness with symptoms such as nausea, weight loss, abdominal pain, diarrhea, and anorexia, although serious complications such as appendicitis have been reported.

The highest prevalence is in developing regions where poor sanitation and animal husbandry practices, and eating inadequately prepared beef, facilitate parasite transmission. Freezing meat at a minimum of minus 10 degrees C (14 degrees F) for no less than 10 days or cooking to a core temperature of at least 60 degrees C (140 degrees F) reduces the risk of infection.

Parasite control
Applying a risk-based approach to meat hygiene requires re-evaluation of traditional practices and assessment of regulatory and industry resources proportionate to risks. The link between control measures pre- and post-harvest along the food chain and public health outcomes, would help risk managers pinpoint the location at the farm, abattoir, processor and consumer level for food safety interventions, according to the publication.

Experts were given two spreadsheet models as a baseline resource. They illustrated the risks associated with selecting different options by risk managers.

For Trichinella, testing of a substantial number of pigs was needed to reduce risks to very low levels. However, there was a point where testing additional pigs may not result in further meaningful reduction in risk or any benefit to public health.

In countries with a high prevalence of Taenia saginata, risks were relatively high irrespective of the inspection package used, with reduced checks resulting in potentially thousands more cases. However, nations with a low prevalence in slaughter populations had a very low residual risk, and changes to inspections had very little impact on model outputs.

Further development of the spreadsheet model, such as using a Bayesian approach, might allow other inputs to be added to support public health decisions. Evidence-based data on consumer cooking habits of beef or pork in a country will improve the confidence of the output from any models and data on meat treatments by food businesses are also necessary, according to the document.

(To sign up for a free subscription to Food Safety News, click here.)