Trichinellosis: a disease transmitted through undercooked meat
What is trichinellosis and how is it transmitted?
Trichinellosis is a disease that can be transmitted to humans and is caused by parasitic worms belonging to the genus Trichinella spp. It affects a wide range of wild carnivorous, omnivorous and scavenging animals, as well as domestic animals such as dogs, cats, pigs and horses.
The worms are found in larval form in muscle fibres. After a person or animal eats infected meat, the larvae are released and invade the small intestine, where they grow into adult worms and reproduce. The newly produced larvae then migrate to the muscle fibres, where they encyst and remain dormant. Animals, including humans, therefore become infected by consuming raw or undercooked contaminated meat (accidental ingestion can also cause infection in herbivores). Most of the time, infected carcasses do not show any visible lesions.
What are the symptoms?
Trichinellosis can cause severe symptoms in humans, including diarrhoea, fever, facial swelling, muscle pain and, in some cases, neurological signs and vision disorders, with potentially irreversible sequelae. Older people, individuals who have ingested a large quantity of larvae, and those whose diagnosis was delayed may develop neurological or cardiac complications that can be fatal. In pregnant women, the parasite can cause miscarriage or premature birth.
That being said, the number of human trichinellosis cases in France is low, with an average of two cases occurring per year.
What meats carry the highest risk?
Pork is the main source of human infection worldwide. However, in France, since 1998, all indigenous human cases have been linked to wild boar meat that had not been inspected by veterinary services and was undercooked. The only exception occurred in 2015, when cases were reported following the consumption of figatelli sausage produced from illegally slaughtered pigs.
Cases have also been reported in people who have consumed contaminated meat while abroad or following the illegal importation of pork, wild boar or bear meat.
What measures have been taken to control the risk of infection?
European and international regulations and standards (Regulation (EU) 2015/1375, ISO 18743, the WOAH diagnostic manual and the Codex Alimentarius) require the testing at slaughter of pork and meat from other susceptible species (wild boar and horses) intended for human consumption. All free-range pigs, breeding pigs and horses slaughtered in France are systematically tested. Pigs reared in indoor holdings are tested through spot checks (one pig in every 1,000), as they are not considered to pose a risk. Wild boar in game processing plants are systematically tested. Testing is also strongly recommended for wild boar hunted for private consumption. This is carried out at the hunters’ expense and under their responsibility.
What precautions should be taken for meat that has not been tested?
When meat cannot be tested, it should be cooked thoroughly to an internal temperature of 71°C prior to consumption. Domestic freezing cannot be considered a reliable means of eliminating the parasite, since the temperatures required to kill all Trichinella species are not necessarily reached.
Smoking meat is not effective against this parasite. Likewise, the salting of traditionally prepared delicatessen meat products does not, on its own, ensure the destruction of Trichinella britovi larvae; it must be combined with a sufficiently long drying period.
What is ANSES’s role regarding trichinellosis?
Providing scientific and technical support through its reference mandates
The Maisons-Alfort Laboratory for Animal Health is the NRL for foodborne parasites. It carries out reference activities for trichinellosis and several other parasites transmitted to humans through food (Toxoplasma, Cryptosporidium, Giardia, Anisakidae, Cysticercus, Toxocara). The NRL provides support to approved departmental veterinary laboratories and private self-testing laboratories and helps implement a quality assurance plan for the diagnosis of animal trichinellosis. The NRL has been accredited by COFRAC for the direct diagnosis of animal trichinellosis since 2009, while the network of approved laboratories has itself been accredited since late 2016.
The laboratory was also designated by WOAH as a Collaborating Centre for Food-borne Zoonotic Parasites in 2014 and as a Reference Laboratory for trichinellosis in 2026. It works closely with other Collaborating Centres and Reference Laboratories to provide scientific and technical support to WOAH member countries, with the aim of improving the detection and control of trichinellosis.
Conducting research to improve the detection and control of trichinellosis
The aims of ANSES’s research on trichinellosis are to:
- Improve the current analysis method, which is based on visual detection of the parasites,
- Develop new detection approaches, in particular serological tests,
- Develop tools to identify the source of infections,
- Develop vaccines to protect pigs from parasites, especially for countries that do not have the resources to implement systematic meat inspection programmes.
Assessing the risks associated with Trichinella spp.
ANSES has carried out several expert appraisals to assess the risks associated with Trichinella spp. and the management measures taken.
In its opinion of March 2017, the Agency updated the current state of knowledge on T. britovi and T. spirali following the reporting of cases linked to the consumption of figatelli. ANSES pointed out the need to test all at-risk pigs (free-range and breeding pigs) for Trichinella spp. larvae at slaughter. It recommended that the labels of uncooked delicatessen meat products such as figatelli that are intended to be consumed cooked clearly state that they must be cooked thoroughly to destroy any larvae they may contain.
Documenting the monitoring of Trichinella spp. in slaughter animals
Every two years, ANSES publishes a report on the monitoring of Trichinella spp. in slaughter animals in France. This report sets out the results of regulatory testing carried out in pigs, horses and wild boar.