Sarcosporidiosis 

Updated: Apr 16, 2018
Author: Edward Charbek, MD, FCCP; Chief Editor: John L Brusch, MD, FACP 

Overview

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.

Epidemiology

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]

 

Presentation

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.[10]

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.[11]

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.[12]

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.[13]

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.[14] 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.

 

DDx

 

Workup

Laboratory Studies

In intestinal Sarcocystis infection, sporulated sporocysts in freshly voided stool can be found via a flotation technique. Sporocysts contain 4 sporozoites. Kato thick smear is a newly applied technique that is used to examine a larger fecal sample and that utilizes cellophane as a slip cover.[15] In one study, Kato thick smear was found to be highly sensitive, identifying 21 of 22 sarcocyst-infected stool samples, while direct smear identified only 1 of the 22 infected samples.[16]

CBC count usually reveals eosinophilia.[17] In cases of sarcosporidiosis with accompanying myositis, creatine kinase levels may be elevated.

Polymerase chain reaction (PCR) techniques can be used to exclude Toxoplasma gondii infection.[18]

Indirect immunofluorescent antibody test are genus-specific but not widely available.

A muscle biopsy may be useful in detecting myositis.

Toxoplasma and Sarcocystis organisms are periodic acid-Schiff (PAS)–positive; trypanosomes are PAS-negative.

Imaging Studies

Radiographs of the involved extremity may identify calcified cysts of Taenia solium (ie, cysticercosis)

CT scan or MRI of the extremities may demonstrate the cysts of sarcosporidiosis, which can grow to 5 cm in diameter.

Procedures

Excisional biopsy in the area of the painful muscle swelling can be performed for diagnostic purposes but is not needed therapeutically.[2, 17]

Histologic Findings

Intact sarcocysts observed in muscle are not associated with inflammation. The sarcocysts are septate and rather large (ie, 11 µm X 350 µm), and they can have a thick, radially striated wall. Seven distinct histopathologic types have been described.[19] The tissue form is PAS-positive. After the sarcocysts disintegrate, inflammatory cells can be observed, including lymphocytes and neutrophils and an intense eosinophilic infiltrate surrounding the muscle cyst. Localized vasculitis and fibrosis of the muscle is apparent.[20]

 

Treatment

Medical Care

No specific antiparasitic agent is indicated, as Sarcocystis infection in humans represents the fully formed terminal stage of the parasite. Corticosteroids can be used to reduce the inflammation associated with Sarcocystis muscular involvement.[5, 21]

Surgical Care

As discussed above, excisional biopsy in the area of the painful muscle swelling is occasionally performed for diagnostic purposes but is not generally indicated.[2, 11]

Consultations

If the history and physical examination findings suggest parasitic infection, consultation with an infectious disease specialist, specifically one familiar with tropical medicine, may be indicated.

Diet

Sarcocysts have been detected in a large percentage of the world’s beef cows and, to a lesser extent, pigs, camels, sheep, horses, and other domesticated animals.[22, 23] Because of this, all associated meat products should be properly cooked before consumption. It is recommended that beef and pork be cooked at 100°C for 4 minutes or frozen to -4°C for 48 hours before consumption. Food suspected of being contaminated with feces or dirt should be avoided in all circumstances.

Activity

Because sarcosporidiosis is usually found incidentally and the human host is typically asymptomatic, no activity restrictions apply, even in persons with confirmed infection. If the patient is experiencing significant myalgias, activity can be directed as tolerated, but no studies have shown that the level of activity affects morbidity or mortality in persons with sarcosporidiosis.

Prevention

No vaccines are currently available for Sarcocystis infection. General hygiene and proper cooking of meat products remain the mainstays of prevention.

Boiling water when contamination with Sarcocystis is suspected provides disinfection. Chemical disinfection with chlorine does not provide adequate disinfection; however, filtering with a small-pore filter does.[24, 25]

 

Medication

Medication Summary

Metronidazole and cotrimoxazole are reportedly being used in eosinophilic myositis, although no specific outcomes have been studied. One case report described cure of Sarcocystis infection with cotrimoxazole. Corticosteroids can be used to reduce inflammation associated with muscular involvement.

Corticosteroids

Class Summary

These agents are used to treat allergic and inflammatory conditions.

Prednisone (Deltasone, Orasone, Meticorten)

Used to treat various diseases, including connective tissue disease and inflammatory and allergic disorders. In addition, it is used for adrenocortical insufficiency, neoplastic diseases, and organ transplantation.

Antibiotics

Class Summary

Therapy must be comprehensive and cover all likely pathogens in the context of this clinical setting.

Sulfamethoxazole (SMZ) and trimethoprim (TMP) (Bactrim, Bactrim DS, Septra, Septra DS)

Used to treat various infectious diseases, including urinary tract infections (not due to pseudomonads), Pneumocystis carinii infection, and staphylococcal infections.

Metronidazole (Flagyl)

Imidazole ring-based antibiotic active against various anaerobic bacteria and protozoa. Used in combination with other antimicrobial agents (except for Clostridium difficile enterocolitis).

 

Follow-up

Further Outpatient Care

Patients with the enteric form of sarcosporidiosis may be tested to document clearance of the sarcocyst from their stool. Note that shedding can continue for up to 6 months.

Further Inpatient Care

Inpatient care is not typically indicated in the absence of a serious co-morbidity such as myocarditis or severe diarrhea with accompanying dehydration.

Inpatient & Outpatient Medications

Oral corticosteroids are indicated in the outpatient setting for symptomatic inflammatory muscular involvement.

Deterrence/Prevention

Instruct patients not to eat raw beef or pork if the risk of sarcosporidiosis is present in the community.

Practice good food hygiene to prevent fecal-oral transmission of this parasite.

Ensure that meat is properly cooked or frozen (see Diet).

Complications

Serious complications may include dehydration, eosinophilic enteritis, and ulcerative obstructive entercolitis.[26]

Prognosis

Sarcosporidiosis is a self-limited disease that carries an excellent prognosis. Rarely, eosinophilic myositis symptoms can persist for many years, recurring when further cyst wall deterioration occurs.

Patient Education

Sarcosporidiosis is a significant food-borne zoonotic infection and is a risk in travelers to and from Southeast Asia. Persons who shed infected oocysts in their stool can spread the infection to others through the fecal-oral route if sanitation is poor. Instruct patients not to eat raw beef or pork and to practice good food hygiene. It should also be emphasized that Sarcocystis infection has been found in other common species such as sheep, horses, and camels.[22] Patients should understand that sarcosporidiosis does not necessitate routine treatment and is usually an incidental finding discovered on muscle biopsy.