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].

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

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.