Sources of human microsporidial infection remain speculative, but possible animal reservoirs are emerging. Of the common human microsporidial infections,Enterocytozoon bieneusihas now been identified in non-human primates, pigs, dogs and a cat;Encephalitozoon intestinalisin dogs, pigs, cows, goats and donkeys andEncephalitozoon hellemin budgerigars and parrots. Evidence of species heterogeneity is also emerging suggesting that some animal isolates may be distinctive. Further molecular epidemiological studies need to be undertaken to clarify which animal genotypes can also infect humans. Some of the less common microsporidial infections found in humans, such as those involvingPleistophora-like species, may be the result of infrequent accidental exposure (for example, inadequately cooked infected fish muscle) and establishment, particularly if the individual is severely immunocompromised.