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), Ig M, and IgG were monitored by an enzyme immunoassay in C. parvum-infect ed calves after medication with halofuginone lactate. In a first exper iment, four groups of five 1-day-old colostrum-fed calves were inocula ted with 10(6) oocysts of C. parvum. They were medicated with 0, 30, 6 0, or 120 mug of halofuginone lactate per kg from days 2 to 8 postinfe ction (p.i.). Unmedicated calves passed large numbers of oocysts betwe en 3 and 14 days p.i. Treatment with 30 mug/kg did not completely inhi bit oocyst output during medication, whereas 60 and 120 mug/kg did. Th e latter groups passed only a reduced number of oocysts when the drug was withdrawn.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 c alves were divided into three groups of 16 or 17 animals each. All ani mals had acquired C. parvum infection before arrival at the fattening unit. They were medicated with 0, 60, or 120 mug/kg for 7 days beginni ng on the day of arrival. Unmedicated calves passed large numbers of o ocysts from 0 to 21 days. Medication stopped oocyst output at day 7, b ut 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. Ris ing coproantibody levels coincided with falling oocyst output. In halo fuginone-medicated and experimentally infected calves, only specific a nti-C. parvum IgM levels rose during the first 5 days p.i. Specific Ig A levels increased in association with oocyst output after withdrawal of the drug in the 60- and 120-mug/kg groups. In naturally infected ca lves, on the other hand, both specific IgA and IgM levels rose further during medication. Although titers were lower than in unmedicated con trols, no significant differences were observed. Both medicated and un medicated calves were equally protected from a challenge with 10(7) oo cysts 16 weeks after the first contact with the parasite.