This study was conducted to assess the prevalence and zoonotic potential of giardiasis in domestic ruminants. Prevalence of infection was 17.7% in sheep and 10.4% in cattle and was significantly higher in lambs and calves (35.6% and 27.7%, respectively). Naturally infected lambs released cysts intermittently for months. Giardia trophozoites from sheep had typical claw hammer-shaped median bodies and were successfully cultured in TYI-S-33 medium, and cytosolic, cytoskeletal, and membrane fractions exhibited protein profiles similar to human isolates (WB). Immunoblotting showed that sera from infected sheep recognized human Giardia, sera from patients with giardiasis recognized Giardia from sheep, and in both cases recognition involved antigenic proteins of similar molecular weight. Cyst output and clinical signs in ovine infection resemble human disease and the organisms infecting humans and ruminants are morphologically and antigenically similar. It is postulated that domestic ruminants may be a reservoir for human infection and vice versa, thus classifying giardiasis as a zooanthroponotic disease.
