J.W. Ngotho

Multiple anthelmintic resistance on a goat farm in Kenya.

The anthelmintic efficacy of benzimidazoles, levamisole, rafoxanide and ivermectin was evaluated on an institutional farm in Kenya using faecal egg count reduction test, larval cultures and a controlled slaughter trial. The results of this study indicated simultaneous resistance of Haemonchus contortus against benzimidazoles, levamisole and rafoxanide and Trichostrongylus columbriformis and Oesophagostomum sp. against levamisole on the same farm. Injectable and orally administered ivermectin was effective against the benzimidazole and levamisole resistant H. contortus.

Prevalence of Eimeria species in cattle in Kenya

A total of 620 bovine faecal samples collected from unselected animals brought for post-mortem to the Department of Veterinary Pathology and Microbiology or from animals in the Kabete (Kenya) practice area of the Faculty of Veterinary Medicine were examined to determine the types and prevalence of Eimeria spp. present. Coccidian oocytes were detected in 67.4% of the samples and eight different species of Eimeria were recognized. The species detected (and their prevalence) were E. bovis (79.0%), E. zuernii (60.2%), E. ellipsoidalis (26.1), E. cylindrica (13.4%), E. auburnensis (28.4%), E. alabamensis (10.3%), E. subspherica (5.0%) and E. wyomingensis (6.1%). E. bovis and E. zuernii led to few cases of clinical coccidiosis and the greatest number of E. bovis in one of the samples from the clinical cases was 30,600 oocysts per gram of faeces (OPG). Age and seasonal variation appeared to have an influence on the intensity of infection.

MULTIPLE AND MULTIGENERIC ANTHELMINTIC RESISTANCE ON A SHEEP FARM IN KENYA

The anthelmintic efficacy of benzimidazoles (albendazole, fenbendazole and oxfendazole), levamisole, oral ivermectin and closantel was evaluated on a farm in Kenya using faecal egg count reduction test, larval cultures and a controlled slaughter trial. The results of this study indicated simultaneous resistance of Haemonchus contortus against benzimidazoles, levamisole and ivermectin, and of Trichostrongylus colubriformis and Oesophagostomum spp. against levamisole on the same farm. Ivermectin resistance developed to 47% within 15 months of first use. Closantel was effective against the benzimidazoles, levamisole and ivermectin resistant H. contortus.

Multiple Anthelmintic Resistance in Haemonchus Contortus on a Sheep Farm in Kenya

Multiple resistance to albendazole, thiophanate, levamisole and orally administered ivermectin was detected in an isolate of Haemonchus contortus in sheep on a farm where benzimidazole resistance had already been identified. Following a faecal egg count reduction test, this was confirmed by both critical and controlled anthelmintic tests. Different groups of sheep infected naturally or given an experimental infection with the benzimidazole-resistant isolate were treated with the recommended doses of various anthelmintics. Compared to the control group, the percentage reductions in the faecal egg counts of sheep treated with albendazole, thiophanate, levamisole and ivermectin varied between 38.2% and 79.1% and the residual worm counts between 27.3% and 57.5%. The results indicate the presence of multiple anthelmintic resistance in this isolate of H. contortus. Sheep treated with closantel showed 100% reductions in faecal egg and worm counts, indicating that this drug was very effective against the population of H. contortus on the farm.

Efficacy of ivermectin delivered from a sustained-release bolus against gastrointestinal nematodes in field grazing calves in Nyandarua district of Kenya

The effect of ivermectin delivered by an orally administered prototype sustained-release (IVM SR) bolus was evaluated over a period of 140 days using 12 steers aged approximately 8-10 months and ranging in weight from 150 to 175 kg. They were allocated to two groups of 6 steers each by restricted randomization based on their liveweight. Each of the treatment group received an IVM SR bolus designed to deliver 12 mg of the ivermectin/day for 135 days. The other group was designated as non-medicated controls. The groups were placed on adjacent 3 acre paddocks obtained by sub-dividing of 6.0 acre permanent pasture which had previously been grazed by young untreated cattle so exposing experimental steers to a similar challenge of a contaminated paddock. The faecal egg counts, herbage larval counts and worm burdens of the major gastro-intestinal nematodes of cattle were significantly reduced by the use of the IVM SR boluses. These parasitological effects were reflected in the increased liveweight gains in the IVM SR bolus-treated steers. The control steers required occasional salvage treatments over the trial period and the herbage on their paddock was heavily contaminated with infective larvae as reflected in the high worm burden in the control steers necropsied at trial termination and in tracer calves introduced into the paddocks during the initial (Day 31), interim (Day 69) and final (Day 100) stages of the experiment.