Trichinella spp. is the parasite responsible for trichinellosis, an animal disease which can be transmitted to humans (zoonosis).
Trichinellosis is found in many wild animals (carnivores, omnivores, carnivorous birds and detritivores) as well as domesticated ones (dogs, cats, pigs, horses) and humans.
Following ingestion, stage L1 (L1M) larvae present in the muscle of ingested meat are liberated from their feeder cells and migrate to the large intestine of the host. After penetrating the intestinal epithelium, they then reach the adult stage. There, adult male and female trichinella worms then mate and the females produce living L1 (newborn L1) juvenile larvae. These newborn L1 larvae migrate from the intestine to the striated skeletal muscles where they can live for many years in this encysted L1M form. Both animals and humans can become infested through the consumption of raw or insufficiently cooked contaminated meat. In most animal cases, there are no obvious signs of infection and no carcass lesions visible to the human eye. However, in humans trichinellosis can cause very serious health problems (diarrhoea, fever, facial swelling, muscle pain, neurological symptoms and vision problems) with potentially permanent damage.
Epidemiology in Europe
Present in every country worldwide, trichinellosis has a major impact on the hygiene and safety of foods of animal origin. European and international regulations (EU regulation 2015/1375, WOAH, CODEX Alimentarius) laying down slaughterhouse screening of pork and other meats liable to be affected, such as wild boar or horse meat, have reduced the disease’s prevalence in the Western world. The main source of human contamination worldwide is pork. In France, however, the only indigenous human cases since 1998 have arisen from the consumption of wild boar meat uninspected by veterinary services, and some human cases in 2015 linked to consumption of figatelli sausages from Corsica. It should be emphasised that the pigs from which the figatelli were made had been slaughtered illegally. Cases imported into France have also been reported following consumption outside of the country of contaminated meat or illegal importation into France of pork, wild boar or bear meat.
European countries have diverging prevalence rates depending on the species likely to be contaminated by Trichinella parasites (pigs, foxes, horses, wild boars, etc.) as well as on eating habits.
Over 1900 human cases have been prevented through the identification of contaminated meat prior to consumption (2 horses, 31 pigs and 4 wild boars).
Disease control methods
Trichinellosis prevention in humans is based on the systematic testing of meats at risk (i.e. pork, wild boar and horse) using a diagnostic test that identifies the parasite following artificial digestion of a muscle sample. When meat cannot be screened, it must be thoroughly cooked (to 71°C). However, freezing meat at home cannot be considered as a reliable method for eradicating the parasite because not only do domestic freezers not take into account parameters such as meat thickness, but they do not always reach -20°C. In addition, certain species such as Trichinella britovi (found in wild boar meat) and T. nativa are even more resistant to cold than T. spiralis.
The parasite is not destroyed by smoking either, and traditional methods for salting pork butchery products do not ensure the inactivation of Trichinella britovi, since they are not always followed by a sufficient drying period. However, cooked pork butchery products such as pâté, rillettes and garlic sausages are Trichinella-free.
ANSES’s Maisons-Alfort Laboratory for Animal Health is the National Reference Laboratory (NRL) for food-borne parasites. It carries out reference activities for trichinellosis as well as a number of other foodborne parasites (Toxoplasma, Cryptosporidium, Giardia, Anisakidae, Cysticercus). It provides scientific and technical support to approved Departmental Veterinary Laboratories (LVDs) (59 laboratories to date) and to laboratories without internal monitoring (3 laboratories). It also runs a quality assurance plan for the diagnosis of animal trichinellosis.
This quality assurance plan was set up in 1998, initially including training courses for veterinary lab technicians (offered every year), the use of a reliable detection technique (in compliance with EU Regulation 2015/1375, Annexe I, chapter I) and the coordination of Inter-Laboratory Aptitude Tests (ILATs). In 2004, France was one of the first European countries to instigate ILATs for all the LVDs in the national network, leading to accreditation by the Ministry of Agriculture which is renewed based on annual ILAT success.
The NRL has been accredited by COFRAC for the direct diagnosis of animal trichinellosis since 2009. The entire network of approved laboratories has been accredited since late 2016.
Currently, all free-range pigs, all breeding sows and all horses slaughtered in continental France undergo inspection, in compliance with EU regulations. Pigs in the intensive breeding sector are sample-checked (1 out of every 1000 pigs) because they are not considered to be at risk. Wild boars sent to processing plants are systematically tested. However, while it is strongly recommended to test boars hunted and killed privately, the hunters themselves must ask and pay for the test. Information on the risks of trichinellosis is circulated among hunting federations.
Since 2014, the NRL has also become Collaborating Centre (CC) for the World Organisation for Animal Health (WOAH) for food-borne zoonotic parasites. This WOAH CC works in collaboration with two other WOAH counterpart centres, one in Canada, and the other in China. The strategy for Trichinella spp. is to combat this parasite responsible for this major zoonosis by ensuring reliable veterinary diagnosis, setting up medical prophylaxis in endemic areas and organising veterinary control measures in France, Europe and internationally in conjunction with the European Union Reference Laboratory and the International Commission on Trichinellosis (ICT).
The NRL coordinated European research activities on trichinellosis from 1999 to 2009 (European contracts TRICHIPORSE, then TRICHINET and TRICHIMED in the MedVetNet network of excellence).
ANSES has published a series of opinions and expert assessment documents in order to evaluate the risk associated with Trichinella spp.
In its latest opinion, dated 14 March 2017, ANSES provided an update of knowledge on T. britovi and T. spiralis, including the important modelling work based on recent human cases of trichinellosis that was conducted in order to update the dose-response relationship.
In its conclusions, ANSES emphasised the importance of analysing all slaughtered pigs in search of Trichinella spp. larvae. ANSES also insists that raw pork butchery products destined to be eaten cooked, such as figatelli, be clearly labelled. Consumer instructions must be easy to read and clearly indicate that such products are to be thoroughly cooked in order to destroy any larvae they may contain.