Blastocystosis - Classification

Classification

Physicians have produced conflicting reports regarding whether Blastocystis causes disease in humans. These reports resulted in a brief debate in medical journals in the early 1990s between some physicians in the United States who believed that Blastocystis was harmless, and physicians in the United States and overseas who believed it could cause disease.

At the time, it was common practice to identify all Blastocystis from humans as Blastocystis hominis, while Blastocystis from animals was identified differently (i.e. Blastocystis ratti from rats). Research performed since then has shown that the concept of Blastocystis hominis as a unique species of Blastocystis infecting humans is not supported by microbiological findings. Although one species group associated with primates was found, it was also discovered that humans can acquire infection from any one of nine species groups of Blastocystis which are also carried by cattle, pigs, rodents, chickens, pheasants, monkeys, dogs and other animals. Research has suggested that some types produce few or no symptoms, while others producing illness and intestinal inflammation. Researchers have suggested conflicting reports may be due to the practice of naming all Blastocystis from humans Blastocystis hominis and have proposed discontinuing the use of that term.

A standard naming system for Blastocystis organisms from humans and animals has been proposed which names Blastocystis isolates according to the genetic identity of the Blastocystis organism rather than the host. The naming system used identifies all isolates as Blastocystis sp. subtype nn where nn is a number from 1 to 9 indicating the species group of the Blastocystis organism. The identification of the species can not be performed with a microscope at this time, because the different species look alike. Identification requires equipment for genetic analysis that is common in microbiology laboratories, but not available to most physicians. Some new scientific papers have begun using the standard naming system.