SPECIFIC SERUM AND LOCAL ANTIBODY-RESPONSES AGAINST CRYPTOSPORIDIUM-PARVUM DURING MEDICATION OF CALVES WITH HALOFUGINONE LACTATE

Fecal and serum anti-Cryptosporidium parvum immunoglobulin A (IgA), IgM, and IgG were monitored by an enzyme immunoassay in C. parvum-infected calves after medication with halofuginone lactate. In a first experiment, four groups of five 1-day-old colostrum-fed calves were inoculated with 10(6) oocysts of C. parvum. They were medicated with 0, 30, 60, or 120 mug of halofuginone lactate per kg from days 2 to 8 postinfection (p.i.). Unmedicated calves passed large numbers of oocysts between 3 and 14 days p.i. Treatment with 30 mug/kg did not completely inhibit oocyst output during medication, whereas 60 and 120 mug/kg did. The latter groups passed only a reduced number of oocysts when the drug was withdrawn. In a second experiment, 3- to 6-day-old colostrum-fed calves were divided into three groups of 16 or 17 animals each. All animals had acquired C. parvum infection before arrival at the fattening unit. They were medicated with 0, 60, or 120 mug/kg for 7 days beginning on the day of arrival. Unmedicated calves passed large numbers of oocysts from 0 to 21 days. Medication stopped oocyst output at day 7, but some of the calves again passed low numbers of oocysts 7 days after withdrawal of the drug. Experimental infection of unmedicated calves was followed by a rise in local anti-C. parvum IgA and IgM titers. Rising coproantibody levels coincided with falling oocyst output. In halofuginone-medicated and experimentally infected calves, only specific anti-C. parvum IgM levels rose during the first 5 days p.i. Specific IgA levels increased in association with oocyst output after withdrawal of the drug in the 60- and 120-mug/kg groups. In naturally infected calves, on the other hand, both specific IgA and IgM levels rose further during medication. Although titers were lower than in unmedicated controls, no significant differences were observed. Both medicated and unmedicated calves were equally protected from a challenge with 10(7) oocysts 16 weeks after the first contact with the parasite.