Eosinophilic Myositis Due to Sarcocystosis
Abstract & commentary
Synopsis: A small group of U.S. Air Force Special Forces members developed eosinophilia and myositis apparently due to infection with Sarcocystis.
Source: Arness MK, et al. An outbreak of acute eosinophilic myositis attributed to human Sarcocystis parasitism. Am J Trop Med Hyg 1999;61:548-553.
In 1993, 10 members of a u.s. air force special Forces team participated in a joint U.S.-Malaysia civic action project, living under local conditions in a jungle village 80 km from Kuala Lumpur.
One week after their return, one of the 10 developed diarrhea followed by myalgias and arthralgias with transient pruritic skin eruptions, cough, headache, night sweats, fever, and rigors. He also developed gradual muscle wasting with intermittent fasciculations. Symptoms ebbed and flowed over the next four months during which he developed firm, fixed subcutaneous nodules as well as transient lymphadenopathy. Symptoms largely resolved over a six-month period, as did his 9-19% eosinophilia and elevated serum creatine phosphokinase.
Approximately 6-8 months later, however, his muscle symptoms and cough recurred and he was given a 15-day course of albendazole that was followed by the immediate development of pruritus. Although the myalgic symptoms gradually improved, they subsequently again recurred and albendazole was readministered, this time for 20 days and in higher dose.
Five additional members of the team also developed, to varying degrees, a similar acute illness. In these cases, however, the illness spontaneously resolved over six months without apparent subsequent relapse. Another individual who had remained in support camp was found to have serological evidence of asymptomatic infection.
Review of the cases found that the total eosinophil count ranged from 440/mm3-2100/mm3 and CK from 321-2212 U/L. Muscle biopsy in the first case described above demonstrated focal collections of Sarcocystis within cysts (sarcocysts); although a tissue reaction was absent immediately adjacent to the cysts, mild eosinophilia and acute inflammation were present in areas not abutting the sarcocysts. Four of four symptomatic members had detectable antibody to Sarcocystis.
Comment by stan deresinski, md
Sarcocystis is, along with Isospora belli, Cryptosporidium parvum, and Cyclospora cayetanensis, a coccidial intestinal sporozoan that infects humans. Toxoplasma gondii is an intestinal sporozoan of cats, but does not usually affect the intestinal tract of humans. Human infection has been associated with ingestion of cyst-infested undercooked meat, with S. suihominis acquired from pork and S. hominis (S. bovihominis) acquired from beef. Intestinal sarcocystosis is usually asymptomatic. Ingestion by humans of sporocysts shed in feces results in the release of sporozoites in the small bowel with penetration of the mucosa. This is followed by schrogony and release of merozoites into the bloodstream with subsequent potential infection of muscle.
Sarcosytosis is highly prevalent in domestic livestock in most of the world. For example, 57.7% of 1362 sheep examined in one province of Iran had evidence of sarcocystosis.1 In addition, a wide variety of other animals may be infected; in Malaysia, the major definitive host is believed to be a monkey-eating python.
Although, as indicated by Arness and colleagues, only 52 cases of human sarcocystosis of muscle have been reported in the medical literature, the infection is undoubtedly not rare in many countries, especially within southeast Asia. In fact, a post-mortem study in Malaysia found sarcocysts in 21 of 100 human tongues examined.2 In addition, Sarcocystis sp. were detected in the stool of 23.2% of 362 asymptomatic Thai laborers as well as in excess of 10% of 1008 Laotians evaluated in an epidemiological study.3,4
Sarcocystis may involve cardiac as well as skeletal muscle. Arness et al indicate that 41 confirmed cases of human sarcocystosis of skeletal muscle and 11 of myocardial muscle have been reported. In addition to muscle involvement, this protozoan has been associated with cases of segmental enteritis in Thailand.5
Many of the patients described here had peripheral blood eosinophilia in association with their symptoms of myositis. The differential diagnosis of eosinophilic myositis includes trichinosis, cysticercosis, polyarteritis nodosa, eosinophilic fasciitis, idiopathic hypereosinophilic syndrome, relapsing eosinophilic perimyositis, and eosinophilia-myalgia syndrome due to L-tryptophan ingestion. Cases of diffuse fasciitis with associated myositis and eosinophilia have been associated with Borrelia burgdorferii infection.6 Eosinophilia with myalgia may also be a reflection of a drug reaction.7
Based on their risky behavior, the patients described in this study may have gotten off easy. The following is a description of some of their activities in Malaysia: "Seasonal monsoon rains were particularly heavy, but the team continued to work, and at times went shirtless and shoeless in the heavy rain, and were given to sport in the ankle deep mud. They later reported extensive physical contact with soil, including exposure to the eyes, nose, and mouth from mud wrestling. They also went swimming in fresh water pools, drank untreated water, and consumed native foods, including lizard meat, soups, and fresh vegetables that were often not well cooked. Compliance with daily doxycycline anti-malarial prophylaxis was irregular at best, and none at all in some cases."
References
1. Oryan A, et al. The distribution pattern of Sarcocystis species, their transmission and pathogenesis in sheep in Fars province of Iran. Vet Res Commun 1996;20: 243-253.
2. Wong KT, Pathmanathan R. High prevalence of human skeletal muscle sarcocystosis in southeast Asia. Trans R Soc Trop Med Hyg 1992;86:631-632.
3. Wilairatana P, et al. Intestinal sarcocystosis in Thai laborers. Southeast Asian J Trop Med Public Health 1996;27:43-46.
4. Giboda M, et al. Current status of food-borne parasitic zoonoses in Laos. Southeast Asian J Trop Med Public Health 1991;22:56-61.
5. Bunyaratvej S, et al. Human intestinal sarcosporidiosis: Report of six cases. Am J Trop Med Hyg 1982; 31:36-41.
6. Granter SR, et al. Borrelial fasciitis: Diffuse fasciitis and peripheral eosinophilia associated with Borrelia infection. Am J Dermatopathol 1996;18:465-473.
7. Smith JD, et al. Possible lansoprazole-induced eosinophilic syndrome. Ann Pharmacother 1998; 32:196-200.
Which of the following is correct?
a. Sarcocystis is a metazoan parasite that induces intense eosinophilia.
b. Sarcocystis may involve skeletal, but not cardiac, muscle.
c. Sarcosystis infection is believed to be transmitted by mosquito vectors.
d. Sarcocystis infection may be acquired by eating undercooked pork.
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