Background: The studies reported here were conducted to assess the efficacy of ivermectin long-acting injection (IVM LAI; IVOMEC® GOLD, Merial; 3.15 % w/v ivermectin) for the treatment and control of natural infestations of cattle by Hypoderma bovis and Hypoderma lineatum, which are the most economically important oestrid flies of cattle in the northern hemisphere.
Methods: Cattle selected from herds with a history of Hypoderma infestation were grouped into blocks of three (Italy, 33 cattle; Germany, 30 cattle) or two (USA, 16 cattle) animals each, on the basis of positivity at the pre-treatment anti-Hypoderma antibody titres. Within each block, animals were randomly allocated to one of the following treatment regimens: saline (control); IVM LAI, administered at the predicted time of occurrence of first-instar larvae (Italy, Germany, USA); IVM LAI, administered at the predicted time of occurrence of second- and/or third-instar larvae (Italy, Germany). All treatments were administered by subcutaneous injection in correspondence of the area anterior to the shoulder at 1 ml/50 kg body weight, which corresponds to 630 mcg IVM/kg for IVM LAI.
Results: No Hypoderma larvae emerged from animals treated with IVM LAI, whereas live H. lineatum (Italy) or H. bovis (Germany, USA) larvae were collected from saline-treated animals (P < 0.01). No adverse reactions to treatments were in any of the animals enrolled in the study.
Conclusions: The results from this study demonstrate that ivermectin in a long-acting formulation is 100 % efficacious in the treatment of cattle naturally infested by H. bovis and H. lineatum larvae at all stages of development. IVM LAI can, therefore, be used as 'prophylactic' treatment for Hypoderma spp. infestations in absence of external evidence of their presence and thus prior to skin and carcass damage, and as 'therapeutic' treatment, when warbles are already present.
Keywords: Cattle; Efficacy; Hypoderma bovis; Hypoderma lineatum; Ivermectin; Long-acting injection.