Trichinosis, also known as trichinellosis, is a parasitic disease caused by roundworms of the Trichinella genus. During the initial infection, invasion of the intestines can result in diarrhea, abdominal pain, and vomiting. Migration of larvae to muscle, which occurs about a week after being infected, can cause swelling of the face, inflammation of the whites of the eyes, fever, muscle pains, and a rash. Minor infection may be without symptoms. Complications may include inflammation of heart muscle, central nervous system involvement, and inflammation of the lungs. Trichinosis is mainly spread when undercooked meat containing Trichinella cysts is eaten. Wild meat is more likely to contain the parasite. In North America this is most often bear, but infection can also occur from pork, boar, and dog meat. Several species of Trichinella can cause disease, with T. spiralis being the most common. After the infected meat has been eaten, the larvae are released from their cysts in the stomach. They then invade the wall of the small intestine, where they develop into adult worms. After one week, the females release new larvae that migrate to voluntarily controlled muscles, where they form cysts. The diagnosis is usually based on symptoms and confirmed by finding specific antibodies in the blood, or larvae on tissue biopsy. The best way to prevent trichinosis is to fully cook meat. A food thermometer can verify that the temperature inside the meat is high enough. Infection is typically treated with antiparasitic medication such as albendazole or mebendazole. Rapid treatment may kill adult worms and thereby stop further worsening of symptoms. Both medications are considered safe but have been associated with side effects such as bone marrow suppression. Their use during pregnancy or in children under the age of 2 years is poorly studied but appears to be safe. Treatment with steroids is sometimes also required in severe cases. Without treatment, symptoms typically resolve within three months. Worldwide, about 10,000 trichinosis infections occur a year. At least 55 countries including the United States, China, Argentina, and Russia have had recently documented cases. While trichinosis does occur in the tropics, it is actually less common there. Rates of trichinosis in the United States have decreased from about 400 cases per year in the 1940s to 20 or fewer per year in the 2000s. The risk of death from infection is low.
Signs and symptoms The great majority of trichinosis infections have either minor or no symptoms and no complications. The two main phases for the infection are enteral (affecting the intestines) and parenteral (outside the intestines). The symptoms vary depending on the phase, species of Trichinella, the quantity of encysted larvae ingested, age, sex, and host immunity.
Enteral phase A large burden of adult worms in the intestines promotes symptoms such as nausea, heartburn, dyspepsia, and diarrhea from two to seven days after infection, while small worm burdens generally are asymptomatic. Eosinophilia presents early and increases rapidly.
Parenteral phase The severity of symptoms caused by larval migration from the intestines depends on the number of larvae produced. As the larvae migrate through tissue and vessels, the body's inflammatory response results in edema, muscle pain, fever, and weakness. A classic sign of trichinosis is periorbital edema, swelling around the eyes, which may be caused by vasculitis. Splinter hemorrhage in the nails is also a common symptom. They may very rarely cause enough damage to produce serious neurological deficits (such as ataxia or respiratory paralysis) from worms entering the central nervous system (CNS), which is compromised by trichinosis in 10–24% of reported cases of cerebral venous sinus thrombosis, a very rare form of stroke (three or four cases per million annual incidence in adults). Trichinosis can be fatal depending on the severity of the infection; death can occur 4–6 weeks after the infection, and is usually caused by myocarditis, encephalitis, or pneumonia.
Cause
The classical agent is T. spiralis (found worldwide in many carnivorous and omnivorous animals, both domestic and sylvatic (wild), but seven primarily sylvatic species of Trichinella also are now recognized:
Species and characteristics T. spiralis is most adapted to swine, most pathogenic in humans, and is cosmopolitan in distribution. T. britovi is the second-most common species to infect humans; it is distributed throughout Europe, Asia, and northern and western Africa, usually in wild carnivores, crocodiles, birds, wild boar, and domesticated pigs. T. murrelli also infects humans, especially from black bear meat; it is distributed among wild carnivores in North America. T. nativa, which has a high resistance to freezing, is found in the Arctic and subarctic regions; reservoir hosts include polar bears, Arctic foxes, walruses, and other wild game. T. nelsoni, found in East African predators and scavengers, has been documented to cause a few human cases. T. papuae infects both mammals and reptiles, including crocodiles, humans, and wild and domestic pigs; this species, found in Papua New Guinea and Thailand, is also nonencapsulated. T. pseudospiralis infects birds and mammals, and has demonstrated infection in humans; it is a nonencapsulated species. T. zimbabwensis can infect mammals, and possibly humans; this nonencapsulated species was detected in crocodiles in Africa.
Taxonomy Kingdom: Animalia Phylum: Nematoda Class: Adenophorea Order: Trichurida Family: Trichinellidae Genus: Trichinella
Lifecycle
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