The activity of ivermectin against common nematode parasites of sheep was examined in 2 experiments. In the 1st experiment, 14 sheep with naturally acquired infections were assigned to 2 groups of 7 sheep each. Sheep in 1 group were treated with 200 micrograms of ivermectin/kg of body weight and the remainder served as nontreated controls. In the 2nd experiment, 15 sheep with experimentally supplemented infections (including a benzimidazole-resistant strain of Haemonchus contortus) were assigned to 3 groups of 5 each. The 1st group was treated with 200 micrograms of ivermectin/kg, the 2nd was treated with 88 mg of thiabendazole/kg, and the 3rd served as nontreated controls. Ten to 12 days after treatment, all sheep were euthanatized and necropsied, and the parasites they harbored were recovered and identified. Efficacy of ivermectin was excellent (greater than 96%) against Dictyocaulus filaria, H contortus, Ostertagia circumcinta, Marshallagia marshalli, Trichostrongylus axei, T colubriformis, and T vitrinus. Treatment was not as uniformly effective for Nematodirus spathiger (73% to 85%), N filicollis (80% to 96%), Cooperia curticei (92% to 100%), immature nematodes (92% to 100%), and early 4th-stage larvae (46% to 100%). Efficacy of thiabendazole was poor for H contortus (42%) and early 4th-stage larvae in the abomasum (52%), but approached 100% for most of the other parasites.

Parafilaria bovicola in naturally and experimentally infected calves, pathological changes, comparison of lesions found during the pre-patent period with those found during patency, with object of estimating age of lesions by their macroscopic and microscopic appearance

Dermacentor andersoni, transmission of Anaplasma marginale to splenectomized calves by injection of gut homogenates from incubated vs. non-incubated adult ticks

gastrointestinal parasites, horses, anthelmintic efficacy of ivermectin, adverse local or systemic reactions not observed

Eimeria christenseni, Trichostrongylus colubriformis, pygmy goats (exper.), effects of concurrent subclinical infections on liveweight; apparent feed digestibility; balances of calcium, nitrogen, and phosphorus; serum copper and zinc concentrations; and bone matrix mineralization

nematodes, dogs, ivermectin activity; no activity against cestodes

Dirofilaria immitis, Dipetalonema reconditum, prevalence in dogs: Virginia; North Carolina

Parafilaria bovicola, field survey of insect vectors collected from cattle, bleeding-point on cows and prepatent period studies, experimental infection of laboratory-raised Musca autumnalis with third-stage larvae, transmission of third-stage larvae to calves (clinical and pathologic findings)

Fasciola hepatica, calves (exper.), age-related susceptibility to infection determined by fecal egg counts at various sampling times following infection, numbers of flukes in liver of calves at slaughter, and antibody response as evidenced by enzyme-linked immunosorbent assay

Ascaris suum, swine, immune responses monitored by lymphocyte blastogenesis assays, indirect radioimmunoassays, peripheral eosinophil counts, and cutaneous delayed hypersensitivity reactions