Experimental infection of mongrel dogs with Giardia lamblia cysts and cultured trophozoites.

In light of recent epidemiologic data implicating wild and domestic animals in the transmission of giardiasis, a study was undertaken to determine whether mongrel dogs could be infected with Giardia lamblia. After careful screening for stool examination (a minimum of six stools examined per week for three weeks), dogs were challenged orally with G. lamblia cysts from human stool or trophozoites from an axenic culture. Three of eight dogs became infected with cysts, and two of three became infected with trophozoites. Latency periods and the course of cyst excretion were similar to those observed in humans, but the dogs were not clinically ill. These data support the concept of interspecies transmission of Giardia and demonstrate that infection can be transmitted by the trophozoite form as well as by cysts.