Trichinellosis is caused by larvae of roundworms, mainly the species Trichinella (T.) spiralis. To date, four species of trichinella are known in Europe. These pathogens are called trichinella or trichina worms. The last known autochthonous outbreak of disease in humans caused by a domestic pig occurred in 1970 after the consumption of poorly smoked meat from a Trichinella-infected domestic pig that was fed with fox meat.
Trichinellosis is a mammalian zoonosis which occurs worldwide independently of climatic conditions. In Central Europe, trichinellosis occurs only rarely. In some eastern EU countries, the incidence is higher, with most cases occurring in the member states Bulgaria and Romania. Infections are often caused by meat products from wild boar. In wild animals, T. britovi and T. pseudospiralis are found in addition to T. spiralis.
Several animal species can be carriers of the parasites. Domestic pigs, wild boar and horses are host animals. Rodents (e.g. rats) and wild animals (e.g. foxes) are considered reservoirs. Humans represent a false host, as infection is not passed on.
Mode of transmission
Infection occurs through the consumption of raw or insufficiently heated meat containing encapsulated Trichinella larvae (except Trichinella pseudospiralis). Digestive enzymes release the larvae, which mature into small worms in the cells of the upper mucosa of the small intestine within a few days. Female worms begin depositing up to 1,500 larvae as early as four to seven days after ingestion by the host. The young larvae pass through the intestinal mucosa and enter the muscles via the bloodstream, where they can survive encapsulated in muscle cells for years. Oxygen-rich muscles, i.e. muscles with a good blood supply, such as the diaphragm, neck, chewing muscles, muscles of the shoulder girdle or upper arms are preferred.
The incubation period is 5 to 15 days and depends on the number of Trichinella larvae ingested. The number of ingested Trichinella larvae that cause clinical disease in humans varies - more than 70 ingested larvae are likely to cause disease. Transmission from person to person is not possible.
Trichinellosis is a mild to fatal foodborne disease in humans, who are considered highly susceptible hosts. The severity of the disease depends on the number of larvae ingested and the immune response of the individual. Disease symptoms in humans are characterized by fever, abdominal pain and diarrhea in the initial phase. In the later course of the disease, muscle and joint pain as well as typical edema in the facial area are the main symptoms.
Mildly infected patients usually recover without complications by bed rest and with the help of a painkiller. Severe infections are treated with drug therapy against worm larvae infestation. Drug treatment is more successful the earlier it is given.
Heating meat to over 70 °C is considered to kill larvae. Freezing at -15 °C reduces the infectivity of the parasite. Smoking, curing and drying are not sufficient to kill larvae.