Evaluation of nitroxynil and closantel activity using ELISA and egg counts against Fasciola hepatica in experimentally and naturally infected cattle.

The responses of cattle infected with Fasciola hepatica to treatment with nitroxynil or closantel were monitored by faecal egg counts and by ELISA assay of anti-fluke antibodies. A first trial with experimentally infected heifers showed an increase in anti-fluke antibody titre as early as 2 weeks post-infection. Eggs were first detected in the faeces 10 weeks after infection. Egg output increased steadily over the next 8 weeks and then rapidly decreased. Treatment of a 20-week infection with nitroxynil was followed by a slow decrease in antibody titre 4 weeks later. This decrease continued over the next 40 weeks, but returned to pre-infection levels in only 2 out of 4 animals. The faecal egg count fell to zero 2 weeks after treatment and remained so for the following 30 weeks, although 1 animal produced a few eggs 32 and 34 weeks post-treatment. Within this period, neither diagnostic technique discriminated between this persistently infected animal and the others. In a second trial, 45 cattle from a naturally infected herd were treated with nitroxynil or closantel. The faecal egg counts of the treated cattle were zero within the following 2 months, whereas there were eggs in the faeces of the control (untreated) group. Nevertheless, the treated cattle showed a small, non-significant drop in anti-fluke antibody titre. These results demonstrate the need for new tools to monitor and evaluate accurately the efficacy of anthelmintic treatment.