Hypodermyiasis

Abstract: A simplified list of the principal Diptera capable of causing myiasis is followed by a brief presentation of the biology, lesions inflicted, and methods of treatment and control of the myiases of economic importance. Cochliomyiasis caused by Cochliomyia hominivorax is of greatest interest, in view of the damage and losses caused by this disease. A brief account of the outbreak of infestation in Libya illustrates the danger of this parasite. Other important traumatic myiases are described: that due to Chrysomya bezziana, which causes an African myiasis similar to cochliomyiasis, and those due to Lucilia cuprina and related species. Hypodermyiasis (warble fly infestation) and oestrosis (nasal bot fly infestation in sheep) still cause major economic losses in domestic animals, justifying their inclusion in control campaigns. The same applies to stomach bot flies of the family Gasterophilidae. The account of each myiasis includes notes on parasiticides which have been found to be effective. Given the rapidity with which a parasite can now be transported from one continent to another, it is important for Veterinary Services to be well-informed and vigilant.

Abstract: 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. 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. 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. 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.