Efficacy of azithromycin dihydrate in treatment of cryptosporidiosis in naturally infected dairy calves.

The objective of this study was to evaluate the therapeutic efficacy of azithromycin treatment of cryptosporidiosis in naturally infected calves under field conditions. Fifty Holstein calves with cryptosporidiosis infection were divided into 5 groups: 1 group (10 calves) was unmedicated and served as the control group and was given distilled water only, whereas the other groups (10 animals per group) were medicated orally with azithromycin at the doses of 500 (group 1), 1,000 (group 2), 1,500 (group 3), and 2,000 mg (group 4) PO once daily for 7 days. The animals were examined clinically and fecal samples were collected on the 1st (inclusion day), 7th, 14th, and 21st days of the study. Drug efficacy was assessed by evaluating diarrhea, oocyst shedding, and weight gains from days 1 to 21 (4 assessments). Significant differences were observed in reductions of oocyst shedding (P < .05) and the fecal diarrhea incidence (P < .05) in groups 3 and 4 when compared with groups 1 and 2 and the control group. Weight gain of medicated calves was significantly higher than that of the unmedicated calves throughout the study (P < .05). The drug significantly suppressed oocyst shedding and resulted in significant improvements in clinical signs. Therefore, this suppression may have significant effect on the reduction of environmental contamination by cryptosporidial oocysts. From the economic point view, authors suggest that the most effective dose of azithromycin for the treatment of cryptosporidiosis in calves should be at 1,500 mg/d for 7 days.