Human infections with Sarcocystis species

Abstract

Recurrent outbreaks of muscular sarcocystosis among tourists visiting islands in Malaysia have focused international attention on sarcocystosis, a disease once considered rare in humans. Sarcocystis species require two hosts, definitive and intermediate, to complete their life cycle. Humans can serve as definitive hosts, with intestinal sarcocystosis for two species acquired from eating undercooked meat: Sarcocystis hominis, from beef, and Sarcocystis suihominis, from pork. Symptoms such as nausea, stomachache, and diarrhea vary widely depending on the number of cysts ingested but appear more severe with pork than with beef. Humans serve as intermediate hosts for Sarcocystis nesbitti, a species with a reptilian definitive host, and possibly other unidentified species, acquired by ingesting sporocysts from feces-contaminated food or water and the environment; infections have an early phase of development in vascular endothelium, with illness that is difficult to diagnose; clinical signs include fever, headache, and myalgia. Subsequent development of intramuscular cysts is characterized by myositis. Presumptive diagnosis based on travel history to tropical regions, elevated serum enzyme levels, and eosinophilia is confirmed by finding sarcocysts in muscle biopsy specimens. There is no vaccine or confirmed effective antiparasitic drug for muscular sarcocystosis, but anti-inflammatory drugs may reduce symptoms. Prevention strategies are also discussed.

FIG 1

Humans as definitive (final) hosts for Sarcocystis species.

FIG 2

Humans as aberrant intermediate hosts for Sarcocystis species.

FIG 3

Sarcocystis stages in tissues of intermediate hosts (A to F) and definitive hosts (G to I). Panels A to G show hematoxylin-stained images. All images are of S. cruzi, except panel E, which is an image of S. hominis. (A) Artery with a first-generation multinucleate schizont (arrow) in an endothelial cell. (B) Kidney glomerulus with immature (arrowhead) and mature (arrow) second-generation schizonts. (C) Blood smear with a merozoite in a mononuclear cell. (D) Heart with an immature sarcocyst containing globular metrocytes. (E) Skeletal muscle with a cross section of a mature sarcocyst with a thick striated wall surrounded by a mononuclear cell infiltrate. (F) Skeletal muscle with longitudinal and cross sections of sarcocysts. The was no inflammatory response. (G) Lamina propria of small intestine with a macrogametocyte (arrow). (H) Small intestine with sporulated sporocysts (arrow) (Whipf's polychrome stain). (I) Phase-contrast microscopy of two sporocysts in a fecal float.