Author(s): Douglas Esposito

Infectious Agent

Intracellular coccidian protozoan parasites in the genus Sarcocystis cause sarcosystosis.

Transmission

Intestinal Sarcocystosis

Humans are the natural definitive host for Sarcocystis heydorni, S. hominis, and S. suihominis, acquired by eating undercooked sarcocyst-containing beef or pork.

Muscular Sarcocystosis

Dead-end intermediate host infection with S. nesbitti and possibly other species can occur in humans who ingest food, water, or soil contaminated with the feces from a reptilian sporocyst-shedding definitive host, likely snakes.

Epidemiology

Human intestinal sarcocystosis occurs worldwide, but the prevalence is poorly defined and can vary regionally. Recent outbreaks of symptomatic muscular sarcocystosis among tourists in Malaysia suggest that intermediate-host infection could be a public health concern. Most reported cases have been acquired in the tropics and subtropics, particularly in Southeast Asia; only a few cases have been reported among US travelers and military personnel.

Clinical Presentation

Most people with intestinal sarcocystosis are asymptomatic or experience mild gastroenteritis, but severe illness has been described. Differences in symptoms and illness severity and duration might reflect the number and species of the sarcocysts ingested. The disease is thought to be self-limited in immunocompetent hosts.

Intermediate-host infection can range from asymptomatic to severe and debilitating disease. In people who develop symptoms, onset occurs in the first 2 weeks after infection, and symptoms typically resolve in weeks to months. Some patients can remain symptomatic for years, however. The most common symptoms are arthralgia, cough, fatigue, fever, headache, and myalgias. Less frequent symptoms include diarrhea, nausea, vomiting; lymphadenopathy; rash; wheezing; and symptoms reflecting cardiac involvement (e.g., palpitations). Fever and muscle pain can be relapsing and 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 might reflect a generalized vasculitis, and late-phase disease can coincide with the onset of a diffuse focal myositis.

Diagnosis

Consider intestinal sarcocystosis in patients with gastroenteritis and a history of eating raw or undercooked meat. Oocysts or sporocysts in stool can be confirmed by light or fluorescence microscopy; PCR testing is not widely available, and no serologic assays have been validated for use in humans.

Include muscular sarcocystosis in the differential diagnosis of people presenting with myalgia, with or without fever, and a history of travel to a tropical or subtropical region, especially Malaysia. Diagnosis during the early phase of infection is difficult, however, because of the lack of specificity of symptoms and clinical and laboratory findings. In the absence of an alternative diagnosis, consider serial investigations for evidence of myositis and eosinophilia. In people with myositis, exclude trichinellosis as a possible cause. Confirmation of muscular sarcocystosis requires biopsy and histologic observation of sarcocysts in muscle. Diagnostic assistance is available through the Centers for Disease Control and Prevention (dpdx@cdc.gov).

Treatment

No proven treatments are available for sarcocystosis. Trimethoprim-sulfamethoxazole might act against schizonts in the early phase of muscular sarcocystosis, but data are scant. Glucocorticoids and nonsteroidal anti-inflammatory medications can improve the symptoms associated with myositis.

Prevention

Intestinal sarcocystosis can be prevented by thoroughly cooking or freezing meat, which kills the infective bradyzoites. Travelers can reduce the risk for muscular sarcocystosis by following standard food and water precautions (see Sec. 2, Ch. 8, Food & Water Precautions).

CDC website: Sarcocystosis