Comparative studies of Giardia spp. in small mammals in southern Ontario. II. Host specificity and infectivity of stored cysts

Abstract

Carefully controlled cross transmission experiments showed that some species of Giardia (Giardia simoni from laboratory rats, Giardia muris from laboratory mice, and Giardia peromysci from deer mice) are highly host specific while others are not. Although Giardia microti infected hamsters, and Giardia mesocricetus infected laboratory rats, these species are morphologically dissimilar from the Giardia spp. which are normally found in these animals. This study also shows that there are two varieties or subspecies of G. muris. Giardia muris from laboratory mice and from a feral brown rat were identical in morphology and dimensions, but differed in host specificity.Infectivity of cysts of G. simoni in faecal suspensions stored at three temperatures was tested using the eosin dye test and by administering portions of suspensions to Giardia-free rats at regular intervals. An exponential decrease in the proportion of cysts that resisted penetration by eosin was observed. The rate of decline was temperature dependent. Rats could not be infected when less than approximately 50% of cysts in suspension were eosin negative.Metronidazole (Flagyl) and quinacrine hydrochloride (Atabrine) did not have a prophylactic effect in rats treated for 7 days. Infections were established in animals inoculated with cysts of G. simoni 24 h after cessation of treatment.