The efficacy of topically applied fluazuron and flumethrin in the control of sheep myiasis

Abstract

Small stock farming and production accounted for approximately 8.4% of total animal product based agricultural output in the 2011 / 2012 season in South Africa. Large scale commercial farming aside, small stock farming also takes on an important role in poorer and developing rural areas of South Africa, where small stock are kept for a combination of economic and non-economic reasons including financial investment or security, food and resource production, as well as religious or traditional reasons. Blowflies are Dipterids with complex life cycles and complete metamorphoses, causing damage to hides and frequent death in their ovine hosts, as a result of cutaneous myiasis caused by the larval stages. All economically important blowfly species causing veterinary myiasis belong to the superfamily Oestroidea, which contains the three major families Oestridae, Calliphoridae and Sarcophidae. The two most significant blowfly genera in South Africa, Lucillia and Chrysomya, both belong to the family Calliphoridae. Chemical means of preventing and treating blowfly strike by topical application remains the most widely used method and appears to be indispensable at this stage. New molecules or formulations effective against blowfly strike are constantly being sought and form part of an active field of research. Bayer currently manufactures and markets Drastic Deadline Extreme ®, a pour-on formulation containing flumethrin and fluazuron for the control of blue ticks (Rhipicephalus decoloratus) in cattle; its possible action against blowflies in sheep was investigated in an in-vitro model, subsequent to a pilot pharmacokinetic study evaluating the kinetics of fluazuron when applied topically to sheep in this particular combination. The first objective of the project was to determine whether fluazuron has any effect at all on the development of blowfly larvae. An active ingredient from the same family of compounds, namely triflumeron, has been successfully used for several years to control blowfly strike in sheep in South Africa (Zapp ® Pour on - Bayer), but it was uncertain whether or not fluazuron would be effective. Raw fluazuron was applied to six pieces of beef according to a dose calculation based on the registered dose of the test product in cattle, while another six pieces were treated with saline in a similar fashion (n=6). Each piece of beef was placed in its own container along with six late instar larvae and placed in the incubator at 35°C for a further nine days. In this instance, the treated group demonstrated significant development defects with regard to pupation (uneclosed pupae) when analysed using the Mann-Whitney non-parametric t-test (p = 0.002).