Trichinella

Trichinella

Profile

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 trichinae. 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 domestic pig infested with trichinae.

Occurrence

Trichinellosis is a worldwide mammalian zoonosis that occurs independently of climatic conditions. In Central Europe, trichinellosis is now rare; in some eastern EU countries, incidences are higher, with most cases occurring in Bulgaria and Romania and often caused by meat products from wild boar.

Host animals

Domestic pigs, wild boar and horses are hosts for trichinae. Rodents (e.g. rats) and wild animals (e.g. foxes) are considered as reservoirs. Humans represent a false host, as they cannot transmit trichinae.

Infection route

Infestation 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. Females 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.

Incubation time

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 very likely to cause disease. Infection from person to person is not possible.

Symptoms

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. The symptoms of the disease in humans are characterized in the initial phase by fever, abdominal pain and diarrhea. In the later course of the disease, muscle and joint pain as well as typical edema in the facial area are in the foreground.

Therapy

Slightly 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 carried out.

Prevention

Heating meat to over 70 °C is considered to safely kill larvae. Deep freezing at minus 15 °C reduces the infectivity of the parasite: Smoking, curing and drying are not suitable for killing the larvae.

Situation in Austria

Man

In Austria, human cases of the disease are very rare: In the past 50 years, only so-called "imported" cases of trichinellosis have been registered by the health authorities in Austria. These were persons who became infected with trichinella larvae during a stay abroad or who took infected meat products to Austria, usually in the course of a vacation at home, and became ill in Austria after eating them.

In 2021, 11 cases were registered in the EMS (EMS, as of 30.03.2022).

Human Trichinellosis cases in Austria

Food

In Austria, 5,024,563 domestic pigs, 440 horses and 26,524 wild boars from the wild as well as 80 farmed wild boars were examined for trichinae in 2021 as part of the official meat inspection. In Austrian breeding and fattening pigs as well as horses, no positive trichinae case has been detected for decades.

Animal

Pigs kept indoors are considered free of Trichinella infestation, as the animals have no possibility of ingesting infested fresh meat. The EFSA is critical of the appropriateness of the statutory trichinae examination of domestic pigs. Wild boar, on the other hand, must generally be regarded as possible carriers of trichinosis. Scientific studies have shown that the parasite is also present in the fox population in Austria, with a clear west-east divide in its distribution.

Technical information

Human Medicine

The suspected diagnosis can be confirmed by the detection of specific antibodies in the blood of the patient; in the case of massive infestation, the larvae can be detected in the tissue by histological examination of muscle biopsy specimens.

Veterinary Medicine

Animals that may be carriers of Trichinella and are intended for human consumption must be examined for Trichinella larvae after slaughter or killing and before the meat is placed on the market (Implementing Regulation (EU) 2015/1375; EN ISO 18743/2015). The examination is carried out using the so-called digestion method: A precisely defined amount of muscle by weight of the carcass subject to examination (usually from the area of the diaphragm pillar) is dissolved by means of artificial digestion and the sediment of the digestion liquid is checked under microscopic observation for the presence of Trichinella larvae.

In the event of positive Trichinella detection, the entire carcass is confiscated by the competent veterinary authority and sent for verifiable disposal.

Contact

Leitung

Dr. Michael Dünser

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