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United States Department of Agriculture

Agricultural Research Service

Title: Sarcocystis in Human Infection

Author
item Fayer, Ronald

Submitted to: Clinical Microbiological Reviews
Publication Type: Review Article
Publication Acceptance Date: February 24, 2004
Publication Date: October 1, 2004
Citation: Fayer, R. 2004. Sarcocystis in Human Infection. Clinical Microbiological Reviews. 17:894-902.

Interpretive Summary: Sarcocystis was first reported in 1843 by Miescher as white threadlike cysts in striated muscles and, without a scientific name for the following 20 years, the parasite was simply referred to as Meischer's tubules. In 1865 similar structures in pig muscle were named Sarcocystis meischeriana. Subsequently, when intramuscular cysts were found in a new host, a new Sarcocystis species name was proposed. During much of this time it was not known if Sarcocystis species were protozoa or fungi. It was 1967, 124 years after the first report of Sarcocystis, when the spindle- or crescent-shaped bodies (bradyzoites) in the sarcocysts were studied by electron microscopy and organelles were observed like those seen in other apicomplexan protozoa such as Toxoplasma and Eimeria. The life cycle and all other stages remained unknown until 1970 when an ARS scientist inoculated bradyzoites from sarcocysts in bird muscles into cultured mammalian cells where they underwent development into sexual stages and oocysts. Transmission studies involving Sarcocystis fusiformis, the species name applied to 3 distinct morphological types of sarcocysts found in cattle, provided further clarification of the biology of this once enigmatic group of protozoan parasites. After feeding sarcocysts to different potential definitive hosts- dogs, cats, and humans- S. fusiformis was found to actually encompass 3 species! The new species names S. bovicanis, S. bovifelis, and S. bovihominis (named for the intermediate and definitive hosts) were proposed. These collective findings provide the basis for our understanding the sources of infectious organisms, the transmission dynamics, the criteria for identifying and naming species of Sarcocystis, and the biology critical to prevention and treatment strategies.

Technical Abstract: Sarcocystis was first reported in 1843 by Miescher as white threadlike cysts in striated muscles and, without a scientific name for the following 20 years, the parasite was simply referred to as Meischer's tubules. In 1865 similar structures in pig muscle were named Sarcocystis meischeriana. Subsequently, when intramuscular cysts were found in a new host, a new Sarcocystis species name was proposed. During much of this time it was not known if Sarcocystis species were protozoa or fungi. It was 1967, 124 years after the first report of Sarcocystis, when the spindle- or crescent-shaped bodies (bradyzoites) in the sarcocysts were studied by electron microscopy and organelles were observed like those seen in other apicomplexan protozoa such as Toxoplasma and Eimeria. The life cycle and all other stages remained unknown until 1970 when an ARS scientist inoculated bradyzoites from sarcocysts in bird muscles into cultured mammalian cells where they underwent development into sexual stages and oocysts. Transmission studies involving Sarcocystis fusiformis, the species name applied to 3 distinct morphological types of sarcocysts found in cattle, provided further clarification of the biology of this once enigmatic group of protozoan parasites. After feeding sarcocysts to different potential definitive hosts- dogs, cats, and humans- S. fusiformis was found to actually encompass 3 species! The new species names S. bovicanis, S. bovifelis, and S. bovihominis (named for the intermediate and definitive hosts) were proposed. These collective findings provide the basis for our understanding the sources of infectious organisms, the transmission dynamics, the criteria for identifying and naming species of Sarcocystis, and the biology critical to prevention and treatment strategies.

Last Modified: 7/23/2014
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