Intracellular coccidian protozoan parasites in the genus Sarcocystis.
Humans are the natural definitive host for Sarcocystis hominis and S. suihominis, acquired by eating undercooked sarcocyst-containing beef or pork. Aberrant, dead-end intermediate-host infection can occur in humans with S. nesbitti and possibly other species when food, water, or soil contaminated with the feces from a sporocystshedding definitive host (likely a reptile) are ingested.
Human intestinal sarcocystosis occurs worldwide, but the prevalence is poorly defined and may vary regionally. Outbreaks of symptomatic muscular sarcocystosis among tourists in Malaysia suggest that intermediate-host infection may be of public health significance. Most reported cases have been acquired in the tropics and subtropics, particularly in Southeast Asia.
Most people with intestinal sarcocystosis are asymptomatic or experience mild gastroenteritis, though severe illness has been described. Differences in symptoms and illness severity and duration may reflect the number and species of the sarcocysts ingested. The disease is thought to be self-limited in immunocompetent hosts.
Intermediate-host infection may range from asymptomatic to severe and debilitating. In those with symptoms, onset occurs in the first 2 weeks after infection, and symptoms typically resolve in weeks to months. However, some patients may remain symptomatic for years. The most common symptoms are fever, fatigue, myalgia, headache, cough, and arthralgia. Less frequent are wheezing, nausea, vomiting, diarrhea, rash, lymphadenopathy, and symptoms reflecting cardiac involvement such as palpitations. Fever and muscle pain may be relapsing and can occur in 2 distinct phases: early (beginning during the second week after infection) and late (beginning during the sixth week after infection). Early-phase disease may reflect a generalized vasculitis, and late-phase disease may coincide with the onset of a diffuse focal myositis.
Intestinal sarcocystosis should be considered in patients with gastroenteritis and a history of eating raw or undercooked meat. Oocysts or sporocysts can be confirmed in stool by light or fluorescence microscopy; PCR is not widely available, and no serologic assays have been validated for use in humans.
Muscular sarcocystosis should be considered in people presenting with myalgia, with or without fever, and a history of travel to a tropical or subtropical region, especially Malaysia. However, diagnosis during the early phase of infection is difficult because of the lack of specificity of symptoms and clinical and laboratory findings. In the absence of an alternate diagnosis, serial investigations for evidence of myositis and eosinophilia should be considered. In those with myositis, trichinellosis should be excluded. Confirmation of muscular sarcocystosis requires biopsy and histologic observation of sarcocysts in muscle. Diagnostic assistance is available through CDC (www.cdc.gov/dpdx; firstname.lastname@example.org).
There are no proven medical treatments for sarcocystosis. Trimethoprim-sulfamethoxazole may have activity against schizonts in the early phase of muscular sarcocystosis, but data are scant. Glucocorticoids and nonsteroidal antiinflammatories may improve the symptoms associated with myositis.
Intestinal sarcocystosis can be prevented by thoroughly cooking or freezing meat, which kills the infective bradyzoites. Muscular sarcocystosis can be prevented with standard food and water precautions (see Chapter 2: Food & Water Precautions).
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