INITIAL SYMPTOMS
Diarrhea in the first week (heavy infections) followed by muscle pain, fever, and periorbital edema; "A presumptive clinical diagnosis can be based on fevers, eosinophilia, periorbital edema, and myalgias after a suspect meal." {Harrison ID, p. 1126-7]
COMMENTS
FINDINGS:
The illness caused by this tissue-dwelling nematode varies from mild to fatal. Intestinal worms may cause diarrhea, and eosinophilia is common. Eye symptoms include pain and hemorrhages of the conjunctiva and retina. Excessive sweating and remittent fever follow. Neurological or myocardial complications may occur, usually 3-6 weeks after the onset of fever. [CCDM, p. 623-6] The intestinal phase lasts 1-2 weeks. It may be mild, or severe with abdominal pain. Occasional findings are difficulty speaking, constipation, and lymphadenopathy. Pneumonitis is rare. It appears to be immunologically mediated. Urticaria has been reported. [ID, p. 1507] The intestinal phase is followed by the systemic or muscle phase (begins 2-3 weeks after ingestion). Larvae penetrate the intestinal wall and enter all types of cells where they die except in cardiac and skeletal muscle cells. Larvae turn muscle cells into "nurse cells" in which the larvae can survive for decades. [Cecil, p. 2134] Most patients are asymptomatic. The muscle pain and swelling are occasionally accompanied by fasciculations. Myositis (weakness and myalgia) is often observed first in the extraocular, jaw, and neck muscles and then in limb flexors and back muscles. [PPID, p. 1315, 3444]
COMPLICATIONS:
Complications from heavy infections include myocarditis, encephalitis, meningitis, seizures, and pneumonitis. [Merck Manual, p. 1680] May cause eosinophilic pleural effusion early in course; Bleeding complications (DIC, epistaxis, hemoptysis, and bowel hemorrhage) are not common. Neurological complications include paralysis and delirium. In the USA from 1991 to 1996, 230 cases were reported to the CDC, and only 3 cases were fatal. [Guerrant, p. 945, 770]
LABORATORY:
Marked eosinophilia is present during acute infection and absent later. [Guerrant, p. 943] Leukocytosis is characteristic. [Guerrant, p. 771] If needed, direct examination of muscle biopsy (usually deltoid) for larvae can give definitive diagnosis. Compressed muscle tissue rather than routine histological preparation is recommended. [Wallach, p. 1208]
EPIDEMIOLOGY:
Animal reservoirs include swine, dogs, cats, horses, and wild animals (rats, foxes, wolves, bears, moose, mountain lions, polar bears, wild boars, Arctic marine mammals, hyenas, jackals, lions, leopards, and farmed crocodiles. Human infection occurs after ingestion of undercooked meat, especially pork, containing encysted larvae. [CCDM, p. 624] Regulations in the US, Canada, and EU have virtually eliminated the presence of encysted larvae in pork or beef. [Cecil, p. 2134] Ingestion of wild game (bear) is the most common source in the US. [ABX Guide]
RESERVOIR
Cats, Dogs, Horses, Rodents, Swine, Wild Animals
REFERENCES FOR CASES/YEAR
1. (US) Decline in reported cases because laws prohibit feeding uncooked garbage to pigs; About 12 cases per year are reported in the United States. [Harrison ID, p. 1126] Estimated 52 cases in 1997; [Mead1999: PMID 10511517]
2. (Global) Cases reported in England & Wales: Zero cases from 2003 through 2012; [Public Health England website] 1066 cases were reported in the US in 1975-1981 compared to 72 cases in 1997-2001 (152/yr vs. 14/yr); [ID, p. 1505] Calculate: Use the older US rate and multiply x 20 for global population = 21,320;