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Table 1 Based on a classification system published in January 2007, Blastocystis isolates from humans, animals, and birds are identified as Blastocystis sp. subtypes 1 to 9, as determined by analysis of SSU rRNA sequences [41].

From: Oh my aching gut: irritable bowel syndrome, Blastocystis, and asymptomatic infection

Sub-type # Yoshikawa subtype # (used in some earlier studies)[41] % of Blastocystis isolates in population belonging to this subtype from study in China adjusted for co-infections[43] Results from animal study from Egypt[48] Non-human carriers[12, 74] Characteristics in human infection Detectability +=Difficult +++=Readily Detected[44, 74]
Blastocystis sp. subtype 3 (3) 66% Illness Cows, Pigs Associated with most chronic symptomatic infections [44, 47, 51] +
Blastocystis sp. subtype 1 (1) 28% Illness Death Cows, Pigs, Chickens, Monkeys Associated with many chronic symptomatic infections [44, 47, 51] ++
Blastocystis sp. subtype 2 (5) 5% Not done Dogs, Monkeys Usually asymptomatic [50] or co-infection in symptomatic patients [44] +++
Blastocystis sp. subtype 4 (7) 0.5% Not done Rodents Rare in one population study [43], but was more common in a study of symptomatic patients at clinic [52] ++
Blastocystis sp. subtype 6 (4) 0.5% Illness Birds Rare in one population study [43], but found in a study of symptomatic patients at a clinic [48] Unknown
Blastocystis sp. subtype 5 (6) 0% Not done Pigs Rare in one population study [43] Unknown
Blastocystis sp. subtype 7 (2) 0% No Illness Birds Rare in one population study [43], but found in a study of asymptomatic individuals [48] Unknown
  1. China has completed the only large study on the prevalence of different Blastocystis subtypes in the general population, and that study found most infections were associated with subtypes 1, 2 and 3.