EFFICACY OF FENBENDAZOLE FOR TREATMENT OF GIARDIASIS IN CALVES

Objective-To determine efficacy of fenbendazole for treatment of giard iasis in calves. Animals-Twenty male and 15 female Holstein calves (10 0 to 180 kg), naturally infected with Giardia sp. Procedure-In vitro f enbendazole susceptibility and resistance development was determined f or a ruminant Giardia isolate by use of an adherence assay. Carves wer e treated as follows. group 1, a single administration of 5 mg of fenb endazole/kg of body weight; group 2, a single administration of 10 mg of fenbendazole/kg; group 3, 5 mg of fenbendazole/kg, every 24 hours f or 3 days; group 4, 10 mg of fenbendazole/kg, every 24 hours for 3 day s; group 5, 20 mg of fenbendazole/kg, every 24 hours for 3 days; group 6, 0.833 mg of fenbendazole/kg, even/ 24 hours for 6 days; and group 7, saline solution. Fecal Giardia cysts were counted on days -3 throug h -1 and 1 through 7, 9, 11, 13, 21, and 28 by use of sucrose gradient concentration and staining with a fluorescent monoclonal antibody. Re sults-The 50% adherence inhibition concentration was 0.024 +/- 0.002 m u g/ml, and resistance could not be detected after 5 weeks of continuo us culture at sublethal concentration of fenbendazole (0.01 mu g/ kg). Fenbendazole was 100% effective in eliminating cysts from the feces w ithin 6 days for calves in treatment groups 2-6. Reinfection was obser ved in some calves within the 28-day study period. Conclusions- Fenben dazole is effective in the elimination of Giardia infections in calves , but repeat treatments may be required in reinfected animals. Clinica l Relevance-Fenbendazole is an effective and economical treatment for Giardia-associated diarrhea and growth rate reduction in calves.