eMedicine Specialties > Infectious Diseases > Parasitic Infections

Sarcosporidiosis

Author: Nicholas R Ondrasik, DO, Resident Physician, Department of Internal Medicine, Tripler Army Medical Center
Coauthor(s): Gunther Hsue, MD, Consulting Staff, Department of Infectious Diseases, Chief, Multi-Specialty Clinic, Tripler Army Medical Center; Raphael J Kiel, MD, Associate Professor of Medicine, Wayne State University School of Medicine; Consulting Staff, Infectious Diseases Division, William Beaumont Hospital
Contributor Information and Disclosures

Updated: Aug 7, 2008

Introduction

Background

Sarcosporidiosis is defined as infection with Sarcocystis, which is an intracellular protozoan parasite. Sarcocystis predominantly infects nonhuman animals but can also infect humans.

Many Sarcocystis species exist, all of which are believed to have a requisite two-host life cycle. This life cycle is based on a predator-prey host relationship.¹ In the rare occurrence in which a human is the intermediate, or accidental, host, Sarcocystis organisms can be found in human skeletal and cardiac muscle.^2,3

Humans can also serve as the definitive host for Sarcocystis. This can occur following ingestion of the cysts in raw or undercooked beef or pork. After this invasion, the infective sporozoites replicate before being eliminated in the stool as sporocysts.⁴ Once shed, sporocysts are typically ingested by an intermediate host (usually a cow or pig) and pass into the small intestine of this animal. Once in the intermediate host, the oocysts release motile sporozoites, which initially migrate into arteries throughout the body. They then become merozoites in the blood vessels and, finally, in muscle. Several noninfectious generations develop before finally maturing to become infectious sarcocysts.¹

Pathophysiology

Sarcosporidiosis in humans has two distinct forms. These two forms are differentiated based on whether the individual is serving as a definitive or intermediate host.⁵ Intermediate hosts are infected following ingestion of water or food contaminated with sporocysts from the feces of a carnivore (eg, dog, wolf). After ingestion, sporocysts penetrate the host’s intestinal wall and proliferate in vascular endothelium before disseminating hematogenously. Dissemination leads to invasion of skeletal and cardiac muscle. Because humans are not typically preyed on, these cysts are not given the opportunity to progress through their typical life cycle and eventually disintegrate within the muscle. Disintegration can be accompanied by vasculitis and fibrosis of the tissue (myositis).

Definitive hosts are infected following ingestion of meat contaminated by infective oocysts. After ingestion, the oocysts sexually reproduce and mature in the intestinal tract. Infective oocysts are then shed via the stool (enteritis). This form of the infection does not involve a systemic phase or a subsequent tissue phase. Humans serve as the definitive host in this infectious form.

Frequency

United States

Sarcosporidiosis is distributed worldwide. In the United States, more than 60 cases of muscle involvement by Sarcocystis species have been described, mostly in collections of case reports of 5-10 cases.

Given that sarcosporidiosis is often an incidental finding, the disease is probably underreported.² The definitive form of sarcosporidiosis often causes self-limited nonspecific enteritis and often goes clinically unsuspected.

International

More than 100 species of Sarcocystis have been recognized, and they have worldwide distribution.⁶ Most cases of human sarcosporidiosis have been documented in Southeast Asia, and the disease is predominantly studied there.

Sarcocystis species that are specific for the skeletal-muscle cysts in cattle and pigs are also distributed worldwide, but cultural practices in certain parts of the world (eg, Thailand) lead to higher rates of human infection. One study reported that the incidence of intestinal Sarcocystis infection in Thai laborers was at 23%.⁷ A study of autopsy specimens in patients in Southeast Asia showed a sarcosporidiosis prevalence rate of 21% in 100 consecutive patients evaluated. The seroprevalence of sarcosporidiosis in Malaysia was estimated at 19.8%.

Mortality/Morbidity

Although sarcosporidiosis can involve the heart, only one death from myocarditis has been linked to Sarcocystis infection. This isolated case involved a 36-year-old woman with focal inflammation and myocyte necrosis, which was found upon examination of the myocardium and it contained a cyst that was morphologically identified as that of a Sarcocystis species.⁸

More common manifestations affect intermediate hosts and include painful muscle swellings, fever, and weakness.⁵ Intestinal sarcocystosis, or the definitive form, most commonly produces abdominal pain, diarrhea, and generalized myalgias. Sarcosporidiosis has not been associated with chronic diarrhea or a malabsorptive state.

Race

Sarcosporidiosis has no known racial predilection, but most described cases have been from Southeast Asia.

Sex

Sarcosporidiosis has no known sexual predilection.

Age

Sarcosporidiosis has no known age predilection; however, because muscle involvement clinically occurs after cyst deterioration, adults are more likely to present with skeletal muscle involvement than are children.⁹

Clinical

History

Since most cases of sarcosporidiosis have been documented in Southeast Asia, a travel history and detailed history of recent dietary practices may be of benefit.

Symptoms caused by the myositic form of sarcosporidiosis occasionally include painful muscle swellings accompanied by erythema, muscle tenderness, generalized muscle weakness, and fever. Cardiac involvement is almost always asymptomatic, but sarcosporidiosis has been known to cause second-degree atrioventricular block in sheep.¹⁰

Within a day after ingestion of contaminated beef or pork, individuals who develop the enteritis form of sarcosporidiosis may experience diaphoresis, chills, fever, vomiting, and diarrhea.¹¹

Common Sarcocystis species found in raw kibbe (Middle Eastern dish of lamb and seasonings, eaten cooked or raw) include Sarcocystis hominis, Sarcocystis hirsuta, and Sarcocystis cruzi.¹²

Physical

• In muscle involvement, painful nodular swelling (1-3 cm in diameter) with erythema and tenderness usually occurs following disintegration of the cysts. On occasion, these nodular lesions are accompanied by fever, diffuse myalgias, weakness, and bronchospasm.¹³ This form of infection is extremely rare and has been described in fewer than 100 human cases. This may support the hypothesis that humans are accidental intermediate hosts.¹
• Persons who ingest the oocyst may develop clinically apparent dehydration after acute diarrhea and diffuse abdominal tenderness.

Causes

Humans become infected with intestinal sarcocystosis after eating infected meat. People who ingest undercooked beef or pork are at increased risk of infection. Individuals who practice poor hand hygiene, thus exposing themselves to fecal-oral transmission, are also at an increased risk of acquiring intestinal sarcocystosis.

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