Genetic diversity As many individuals are asymptomatic carriers of D. fragilis, pathogenic and nonpathogenic variants are proposed to exist. A study of D. fragilis isolates from 60 individuals with symptomatic infection in Sydney, Australia, found all were infected with the same genotype, which is the most common worldwide, but differed from the genotype first described from a North American isolate and later also detected in Europe. Transmission Organisms similar to D. fragilis are known to produce a cyst stage that is able to survive outside the host and facilitate infection of new hosts. However, the exact manner in which it is transmitted is not yet known, as the organism is unable to survive outside its human host for more than a few hours after excretion, and no cyst stage has been found. Early theories of transmission suggested D. fragilis was unable to produce a cyst stage in infected humans, but some animal existed that in which it did produce a cyst stage, and this animal was responsible for spreading it. However, no such animal has ever been discovered. A later theory suggested the organism was transmitted by pinworms, which provided protection for the parasite outside the host. DNA has been detected in surface-sterilized eggs of Enterobius vermicularis eggs, thus suggesting the latter may harbor the former. Experimental ingestion of pinworm eggs established infection in two investigators. Numerous studies reported high rates of coinfection with helminthes. However, recent study has failed to show any association between D. fragilis infection and pinworm infection. Parasites similar to D. fragilis are transmitted by consuming water or food contaminated with feces. The high rate (40%) of concomitant infection with other protozoa reported by at St. Vincent's Hospital, Sydney, Australia, supports the oral-fecal route of transmission.
Dientamoebiasis
Thelaziasis
Paragonimiasis
Isosporiasis
Metagonimiasis
Loa loa filariasis
Cyclosporiasis
Toxocariasis