Sheep scab control using trans-cinnamic acid.
A series of in vitro and in vivo assays were conducted to examine the effects of trans-cinnamic acid ethyl ester on Psoroptes mange mites. In vitro, 24h after exposure to the test material at concentrations of 10, 1 or 0.1% (v/v), 100, 74 and 20% of mites had died, respectively, compared to 8% following exposure to the control (0.05% SDS only). The different life-cycle stages were affected similarly by the test compound. The concentration required to produce 95% mortality 24h after exposure to the test compound was 6.29% (95% confidence interval 4.98-8.88). Tarsal contact of the mites with the test compound was also sufficient to achieve high levels of mortality; 100% death was observed when the mites were placed in contact with either sheep skin circles treated to give 0.01 ml/cm(2) or polyester cloth circles treated with 0.03 ml/cm(2). However, the residual activity of both skin and cloth treated with 0.03 ml/cm(2) was completely lost after 7 days. In vivo, trans-cinnamic acid ethyl ester suspended in 2% (w/v) lecithin was applied as a spray formulation to eight sheep with active artificial infestations of sheep scab. Seven of the 8 treated sheep were cured and remained completely clear of scab mites for 56 days. However, 33 days after treatment 2 adult female mites were observed on one of the eight treated sheep and the mite population on this sheep subsequently recovered. In contrast, in a control group of two infested sheep, treated with a 2% (w/v) lecithin only, mite populations increased as expected in a typical scab infestation, but eventually self-cured in one animal. The data suggest that, with appropriate development of suitable application technology, trans-cinnamic acid ethyl ester could have a role as a potential therapeutic treatment for active sheep scab, however the short residual period of activity is likely to limit its use in commercial sheep flocks.
Veterinary Parasitology & Ecology Group, School of Biological Sciences, University of Bristol, BS8 1UG, UK. richard.wall@bristol.ac.uk
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Bates
D000336:Aerosols; D000818:Animals; D002934:Cinnamates / Q000737:chemistry / Q000627:therapeutic use*; D005260:Female; D008297:Male; D008924:Mite Infestations / Q000188:drug therapy / Q000469:parasitology / Q000662:veterinary*; D040042:Psoroptidae / Q000187:drug effects*; D012756:Sheep; D012757:Sheep Diseases / Q000188:drug therapy* / Q000469:parasitology
D000336:Aerosols; D002934:Cinnamates; C029010:cinnamic acid