A modified critical test and its use in two dose titration trials to assess efficacy of praziquantel for Anoplocephala perfoliata in equids.

The research investigated the efficacy of praziquantel for the treatment of Anoplocephala perfoliata, a type of tapeworm, in equids, through two dose titration trials involving 43 subjects.

Study Design

• The study aimed to determine the effectiveness of a 48-hour critical test, the efficacy of an oral paste consisting of 0.5-2.0 mg praziquantel per kg of body weight, and the best time to conduct fecal egg counts for optimal tapeworm prevalence estimation.
• All feces passed by the treated animals within 48 hours were collected and examined for tapeworms in 12-hour batches, with emphasis on tapeworms attached to the mucosa and those unattached.
• Tapeworms were also examined for abnormalities and normality through a stereoscope. Fecal samples were taken at intervals of 6 hours, starting from the treatment time, for egg counts.

Findings

• Of the 36 treated equids, 32 experienced 100% efficacy. The remaining four subjects were given different dosages (0.5, 1.0, 1.5, and 2.0 mg praziquantel/kg body weight), resulting in varying efficacies of 85.5%, 99.7%, 100% and 100% respectively.
• Two equids treated with the lowest dosage exhibited low efficacies of 5.4% and 38.1%, with normal tapeworms found in the ventral colon and, in one subject, also in the dorsal colon.
• In the seven untreated equids, tapeworms were mainly found in the cecum, with 21.3% of those being detached.
• What the paper refers to as “major fragments”, or worms nearly complete sans a scolex, constituting 20.5% of the number of intact worms, were not included in the efficacy analysis, although the authors argue they should be.

Post Treatment Results

• If the two equids that experienced low efficacy are excluded and the number of all tapeworms and major fragments are combined, less than 0.5% were found in feces within 12 hours of treatment, with about 20% in the 12-24-hour period, 42% in the 24-36-hour period, 24% in the 36-48-hour period, and 13.5% in the equids at necropsy.
• One horse passed all its tapeworms within 24 hours following treatment.

Implications

• Compared to a 24-hour test with no feces examination, the 48-hour test was found to be more efficient and accurate for determining efficacy.
• However, the study suggests that protocols akin to the 48-hour test, but with a 24 or 36-hour post-treatment period, should be investigated.
• An optimal tapeworm prevalence estimation can be achieved when fecal samples for egg count are taken 18-24 hours post-treatment.
• The Cornell-Wisconsin centrifugal flotation technique, used for testing, scored a specificity of 100%, and a sensitivity of 94% at 18 and 24 hours.
• The paper concludes with a brief discussion on other ways to assess the efficacy of a treatment for A. perfoliata.