Scientific name. Trichinella spiralis, T. pseudospiralis, T. nativa, T. nelsoni, T. britovi, T. murrelli
Disease name. trichinosis
Trichinella spiralis: cosmopolitan (mainly temperate zones)
T. pseudospiralis: cosmopolitan (mainly temperate zones)
T. nativa: arctic and subartic regions
T. nelsoni: tropical Africa, northern Sahara
T. britovi: Europe, Africa (northern Sahara), northern Arabia, northern Asia, and central Asia
T. murrelli: U.S.A
Infection rate. Infection status can not be estimated. Sporadic outbreaks have been reported in all over the world. Many outbreaks have recently occurred in China, Romania, Argentina, Russia, Serbia, Bulgaria, Croatia, Lebanon and France. In Korea, two times of epidemics were recently occurred with total 8 persons of infection with T. spiralis. The source of infections were the raw flesh of wild raccoon dogs and boars.
Life cycle. When the meat harboring the infective-stage larvae are ingested, the larvae excyst in the stomach or duodenum to invade the mucosal epithelium of small intestine. They then rapidly develop through the 4-larval stages, and mature in second day of infection. The adult worms live intracellularly within the superficial enterocytes of small intestine. After mating, females are inseminated, and begin to produce eggs that develop into minute larvae in the uterus. The larvae come of out the uterus, migrate into the blood stream via intestinal lymphatics or mesentric venules, and finally reach the striated muscles. They become encapsulated within the muscle fibers with exception those of T. pseudospiralis.
Morphology. The adult worms are minute and slender; the females are no more than 2.2 mm long by 90 ㎛ wide, and the males are 1.2 mm long by 60 ㎛ wide. The anterior part is filled with the stichocytes. The larvae encapsulated within the muscle fibers are 0.8 to 1.0 mm long, and they also have stichocytes in the anterior part of body.
Pathology and clinical symptoms. The pathologic changes and the symptomatology are divided into three successive stages, i.e., intestinal, muscle invasion and convalescence. In the intestinal stage, inflammation of the duodenal and jejunal mucosa caused by the penetration and development of the adult worms may produce symptoms of malaise, nausea, diarrhea and abdominal pain. In the stage of muscle invasion, typical manifestations are fever, facial edema, pain, swelling, weakness of involved muscles, and peripheral eosinophilia. In the convalescence stage, fever generally subsides and muscle symptoms begin to decrease.
Diagnosis. The clinical diagnosis is often based on the patient's history of eating raw meat or clinical symptoms such as fever, facial edema, muscle pain and eosinophilia. Definitive diagnosis can be made by demonstration of encapsulated or free larvae from the compressed muscle samples. The xenodiagnosis is useful in surveys to detect viable larvae. Intradermal test and enzyme-linked immunosorbent assay (ELISA) are also useful.
Prevention. Avoiding ingestion of raw or inadequately cooked meat of pigs or wild animals.
Comments. Differential diagnosis from the acute food-poisoning is necessary.
Encysted larvae of Trichinella spiralis. Intact larvae are seen in teased press preparation of muscle. x200
A coiled Trichinella spiralis larva in the biopsied muscle of human.
Larva of T. spiralis isolated from the muscle of human.
T. spiralis larva in the muscle of human case, which was biopsied after treatment with flubendazole and albendazole for 10 days. The larvae detected at the same day were uncoiled and did not show the infectivity in mice and a hamster. (Semichon's acetocarmine stained).
Badger, Meles meles melanogenys, is one of the reservoir host of T. spiralis in Korea.
Sectioned encysted larva of Trichinella spiralis. Well defined encysted larva is seen in host muscle. x200
A sectioned larva of T. spiralis in the worm cyst of muscle biopsied from human. H&E stained.