Trichinellas (Trichinella spiralis, T. nativa, T. britovi, etc.), earlier known as trichins, belong to the nematode worms and are parasites of carnivores. Humans are infected after eating poorly prepared uninspected meat infested with larvae, usually pork, sausage or bear meat.
The larvae are released from the meat and mature and live in the small bowel mucosa. The adult worms produce larvae that travel with the bloodstream to the musculature all over the body and invade the muscle cells.
The larva produces together with the host muscle cell a capsule that remains viable for years and is calcified after dying.
In addition to predators living in the wild nature, trichinellas are to some extent encountered in pigs and in wild boars raised in captivity. Infected animals are destroyed when identified in meat inspection.
Uninspected and poorly prepared meat poses a real infection risk.
Symptoms
The clinical disease usually starts with mild gastrointestinal symptoms (nausea, vomiting, diarrhoea) within a week after infestation.
As the larvae migrate and invade the muscles (1-6 weeks after the infestation), the patient has fever, myalgia, muscle weakness, muscle swellings, oedema in the face and pain around the eyes, haemorrhages under the nails and in the conjunctivae, symptoms of vasculitis, urticaria and occasionally a cough and dyspnoea.
In a violent infection, the larvae that have migrated to the cardiac muscle may cause arrhythmias.
Diagnosis
The suspicion is based on history, eosinophilia and the clinical picture.
According to history, consumption of uninspected meat (e.g. home-slaughtered pork, bear meat).
Eosinophilia is usually strong and is observed about 10 days after infestation, and antibody concentrations rise after 2-3 weeks of this. The blood concentrations of muscle enzymes (creatine kinase, lactate dehydrogenase) and aminotransferases may be increased.
The diagnosis is confirmed either by serology or muscle biopsy. However, the treatment must already be started if there is a strong clinical suspicion. Seroconversion takes place 3-5 weeks after infestation and the larvae can be found in muscle biopsy samples (deltoid or gastrocnemius muscle) most easily on the fourth week.
Health authorities are to be informed about the infection according to national legislation.
Treatment
Consult a specialist on infectious diseases.
Initial treatment of the acute phase consists of rest and NSAIDs; for severe symptoms, glucocorticoids (prednisone 40-60 mg once daily) may be given.
In severe cases, intensive care may be warranted because of increased mortality 3-6 weeks after the infestation.
The treatment of adult worms with antihelminthic drugs does not remove the life-threatening potential of severe infections because the possible inflammatory reaction in the heart, in the central nervous system and in the lungs is caused by larvae that have invaded the tissues.
Adult worms living in the wall of the small intestine produce larvae for several weeks, and hence treatment of adult worms is warranted using albendazole (400 mg twice daily for 10-14 days) or mebendazole(400 mg 3 times daily for 14 days)
Dosage is the same for children, but mebendazole must not be given to children below 1 year of age.
Albendazole may require special license.
Specific medication is combined with a glucocorticoid 40-60 mg once daily for 10-15 days.
An infectious disease specialist should be consulted about treatment during pregnancy. Caution has been excercised in relation to using mebendazole and albendazole during pregnancy because their teratogenicity has been noted in experiments in rats and rabbits, albeit their teratogenicity has not been reported in humans. Therefore, the use of mebendazole and albendazole in the treatment of trichinellosis during the 2nd and 3rd trimester may be warranted.
Prevention
Inspection of meat (regular, thorough)
Proper preparation of meat (over +80 °C). Smoking fish or meat is not sufficient. Freezing (-15 °C for at last 20 days) has earlier been recommended, but at least some species, like Trichinella nativa, stand freezing.
Post-exposure prophylactic medication (mebendazole 5 mg/kg twice daily for 5 days) may beneficial if it is started within 6 days after the patient is known to have eaten meat that contains trichinellas or he/she is strongly suspected to have eaten such meat.
References
Acs N, Bánhidy F, Puhó E, Czeizel AE. Population-based case-control study of mebendazole in pregnant women for birth outcomes. Congenit Anom (Kyoto) 2005 Sep;45(3):85-8. [PubMed]
Torgerson PR, Devleesschauwer B, Praet N et al. World Health Organization Estimates of the Global and Regional Disease Burden of 11 Foodborne Parasitic Diseases, 2010: A Data Synthesis. PLoS Med 2015;12(12):e1001920. [PubMed]
Gottstein B, Pozio E, Nöckler K. Epidemiology, diagnosis, treatment, and control of trichinellosis. Clin Microbiol Rev 2009;22(1):127-45, Table of Contents. [PubMed]