Trichinella spiralis is a nematode (roundworm) that can be found in carnivorous mammals. Humans may acquire it by consuming larvae present in the muscle tissue of domestic or wild animal meat.
Trichinellosis is caused by the ingestion of undercooked meat containing encysted larvae of Trichinella species from a domestic or sylvatic animal. The most frequent mode of transmission is consumption of inadequately cooked pork from domestic pigs.
Trichinellosis can be divided into an intestinal phase and a muscle phase. In the intestinal phase, encysted larvae that are consumed from undercooked meat are liberated by digestive enzymes. This phase may be asymptomatic or present with gastrointestinal disturbances. The muscle phase occurs within 1 month of ingestion and is caused when adult worms in the intestine release new larvae that burrow through the intestinal mucosa, access the bloodstream, and encyst in muscles. This phase presents with symptoms such as myalgia.
The intestinal stage occurs after ingestion when the encysted larvae are released. Larvae then mature into adult worms that burrow into the intestinal mucosa. Female worms release new larvae one week after ingestion. This initial stage may be asymptomatic or may be accompanied by symptoms including abdominal pain, nausea, vomiting, and diarrhea.
The muscle stage occurs after the larvae burrow into the intestinal mucosa and reach the bloodstream. Once they disseminate hematogenously they reach skeletal muscle and encyst. This stage is characterized by inflammation of the affected muscles which is termed myositis. Symptoms of the muscle phase include myalgia, muscle swelling, and weakness.
Fever can also be seen in trichinellosis. This occurs as an inflammatory response to the parasite in muscle tissue.
Patients may present with peritorbital edema and other ocular findings such as conjunctival hemorrhages.
Patients with trichinellosis often have massive eosinophilia with eosinophils count > 5000 mm3 (from 20% to 90% over the course of the disease).
In mild cases, analgesics are enough since the infection is self-limiting. Antihelminthics are indicated in more serious cases with systemic manifestations. Albendazole helps to kill adults thereby limiting the production of new larvae. Steroids are sometimes prescribed to decrease inflammation especially if cardiac, central nervous system, or pulmonary tissue is involved.
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