Rare Parasite Causes Relapsing Febrile Myositis

Humans can become hosts for Sarcocystis species by consuming food or water contaminated with fecal sporocysts from an infected definitive host and in such cases, hematogenous dissemination can occur with invasion of muscle leading to sarcocysts.

Scientists at the University of Malaya (Kuala Lumpur, Malaysia) investigated an outbreak of acute, relapsing febrile myositis that occurred in a group of 92 college students and teachers that had attended a retreat in a hotel located on Pangkor Island, off the west coast of Peninsular Malaysia. Investigations included full blood counts (FBC), renal function tests (RFT), liver function tests (LFT), serum creatine kinase (CK) levels, chest X-rays, blood cultures, and blood films for malarial parasites.

Serological testing was done for Chikungunya virus, Dengue virus, Legionella, Mycoplasma, and Leptospira. Testing was performed using an in-house immunofluorescence assay for detection of chikungunya immunoglobulin M (IgM) and IgG; anti-dengue IgM and IgG capture ELISA (Standard Diagnostics; Yongin, Korea) for detection of dengue IgM and IgG; immunofluorescence assays for detection of Legionella IgG (MarDx Diagnostics, Inc.; Bray, Ireland) and Legionella IgM (Vircell; Granada, Spain); SERODIA-MYCO II (Fujirebio Inc.; Tokyo,Japan) for detection of Mycoplasma total antibodies.

Sarcocystis serology was done by an immunoblot assay using S. neurona merozoite-derived antigens (Centers of Disease Control; Atlanta, GA, USA) in 10 patients. Muscle biopsies from affected sites in four patients with myalgia and Magnetic resonance imaging (MRI) abnormalities were fixed in buffered 10% formalin and routinely processed. Hematoxylin and eosin stained tissue sections were examined by light microscopy. Polymerase chain reaction (PCR) for Sarcocystis spp. was performed on all four biopsies.

Out of four muscle biopsies, sarcocysts were identified in three. S. nesbitti was identified by PCR in three of the four biopsies including one biopsy without an observed sarcocyst. Non-Malaysians had a median duration of symptoms of 27.5 days which was longer than that of 14 days for Malaysians, and the Non-Malaysians were more likely to experience moderate or severe myalgia compared to mild myalgia. None of the other serology tests for dengue, Legionella, Mycoplasma, or Leptospira were consistent with recent infection. Sarcocystis spp. were not detected by PCR in any water samples.

The authors conclude that the similarity of the symptoms and clustered time of onset suggests that all affected persons had muscular sarcocystosis. This was the largest human outbreak of sarcocystosis ever reported, with the specific Sarcocystis species identified. The largely nonspecific clinical features of this illness suggest that S. nesbitti may be an under diagnosed infection in the tropics. The study was published on May 22, 2014, in the journal Public Library of Science Neglected Tropical Diseases.

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