Foodborne and waterborne zoonotic sarcocystosis

• Life cycles of zoonotic species of Sarcocystis are reviewed.
• Outbreaks of acute sarcocystosis due to a S. nesbitti-like parasite are summarized.
• Evidence possibly linking S. nesbitti to human outbreaks or lack of it is reviewed.

The ingestion of raw beef or pork infected with Sarcocystis can cause illness in humans. Nausea and vomiting can occur within three days of consuming infected meat; these symptoms are considered due to toxic substances in sarcocysts or to other factors in raw meat. Diarrhea and abdominal pain are associated with excretion of sporulated sporocysts in human feces usually within 8–14 days after ingestion of infected meat. The intestinal phase is often self-limiting but sporocysts may be excreted for months. There appears to be little or no immunity to excretion of sporocysts after ingesting each infected meal. The clinical illness is more severe after eating infected pork versus infected beef. There is one zoonotic Sarcocystis species in pork, Sarcocystis suihominis, with domestic and wild pigs as intermediate hosts. Two zoonotic species are present in cattle, Sarcocystis hominis, and Sarcocystis heydorni; neither has been recognized in North America. Although isolated human cases of muscular sarcocystosis have been known for more than 100 years, recently a mysterious serious, diagnostically challenging illness has been reported in humans on vacation/travel to Malaysia; sarcocysts were detected histologically in biopsy of muscles from some of these patients. These outbreaks of sarcocystosis-like illness in humans are summarized. Molecular epidemiological evidence suggests a new type of zoonosis linked to ingestion of food and water contaminated with “Sarcocystis nesbitti”. The life cycle of S. nesbitti remains unknown. Maccaque monkeys are thought to be its intermediate hosts and unknown species of snakes as definitive hosts. Evidence possibly linking S. nesbitti to human outbreaks or lack of it is reviewed.