Introduction & Objective: Cryptosporidium is one of the important pathogenic agents of gastero intestinal tract of mammals, especially human and domestic animals. This parasite is one of the principal causative agents of mortality in young animals. Considering the zoonotic importance of the parasite, infected animals can be very dangerous to the public health. This study was performed to determine the prevalence of cryptosporidial infection in humans, cattle, sheep, horses, dogs, domestic fowls and turkeys in Hamadan and its suburbs and also to evaluate the role of the animals of this area in transmission of the infection to human inhabitants of Hamadan.

Materials & Methods: In this cross sectional descriptive study fecal samples were collected from 477 cattle, 220 sheep, 158 horses, 210 dogs, 200 domestic fowls, 200 domestic turkeys and 300 humans in Hamadan city. Cryptosporidium oocysts were concentrated by using the formalin-ether sedimentation method followed by the modified Ziehl-Neelsen staining technique and examined by light microcopy.

Results: The prevalence rate of the infection in cattle, sheep, horses, dogs, domestic fowls, domestic turkeys and humans was 15.93%, 8.6%, 12.6%, 3.8%, 2.5%, 4% and 5.33%, respectively.

Conclusion: Cryptosporidium can cause diarrhea by itself or with other microbial agents in inhabitants of Hamadan. Considering the high prevalence and intensity of the infection in the cattle of the suburbs of Hamadan and with regard to the results of the other researches in the world and Iran, cattle are one of the most important sources of the infection for the inhabitants of Hamadan.