Background & Objectives: Giardia duodenalis is the most common intestinal parasite with cosmopolitan distribution. This parasite has been found in the intestine of humans and other mammalian hosts including cats, dogs, cattle, sheep, deer, pigs and muskrats. It is postulated that animals maybe reservoir for human infection and viceversa. In present study, the possible genetic similarity between cat and humans Giardia and its probable zoonosis were investigated.

  Methods: Direct examination and formalin-ether concentration techniques were performed on stray and semi stray cat fecal specimens. Gradient sucrose method was applied for collection and purification of cysts and DNA extraction was performed by phenol-chloroform and CTAB (Cetyl trimethyl ammonium bromid ( methods. DNA of cysts could hardly be extracted after repeated freezing and thawing. Polymerase chain reaction (PCR) was performed for DNA amplification. In this study triosephosphate isomerase (tpi) gene was selected as a molecular marker. Two sets of primers (PM 290 and PM 924) were considered. Two restriction enzymes RsaI and AvaI were also used to determine restriction fragment length polymorphism (RFLP) for PCR fragments amplified by both primer sets.

  Results: Ten samples were positive for Giardia cysts which were examined for molecular investigation. Four cat isolates were amplified by PM 290. PCR-RFLP patterns were found to be similar to human isolates AC≠AF 069556 (subgroup of AC≠U 57897) with possibility of cross-transmission.

  Conclusion: Therefore the similarity of genomic characters of isolates of cat and human Giardia implies possibility of zoonosis and transmission of these protozoa from cat to human and vice versa.