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Beyond the Bale : Dec 08 - Jan 09
18 Animal health Beyond the BaLe Lousy sheep keep the R&D pipeline spilling over As chemical resistance starts to affect a popular lice-control treatment, R&D efforts are ensuring the continuing availability of viable control options By Gio Braidotti L ice-control failure in sheep treated with insect growth regulator (IGR) products has raised concerns that resistance is emerging among lice populations. Tracking the situations is AWI’s Dr Johann Schröder, who is working to ensure that a viable range of lice detection, control and management options continue to be available to woolgrowers. The NSW Department of Primary Industries (DPI) has been involved in these efforts, with Dr Garry Levot, head of the Parasitology Research Group, working with chemical companies on cases of IGR product failure that are not attributable to management or application errors. In these instances it is necessary to test for chemical resistance, but Dr Levot says cumbersome technology initially stymied these efforts. “Testing for resistance requires a pen trial in which sheep subject to product failure are shorn, treated again, and then checked for lice 20 weeks later,” he says. “We all had an interest in trying to devise a quicker way of diagnosing resistance and we were successful in that.” Since these insecticides prevent lice eggs from hatching, Dr Levot reasoned that resistant lice can lay eggs capable of hatching despite being treated with an insecticide dose sufficient to prevent hatching from eggs laid by normal lice. A laboratory test based on this idea has been devised, which reduces testing times from five months to 19 days. Testing by NSW DPI technical officer Narelle Sales subsequently identified lice populations from diflubenzuron or triflumuron-treated sheep that laid eggs capable of hatching irrespective of the lousicide dose used. “Resistance was not restricted to any particular area,” Dr Levot says. “We found resistant populations in NSW, Western Australia and Queensland. “We encourage people who have a problem in controlling lice with an IGR product to contact the manufacturer in the first instance, so that the company can investigate why the product may not have worked. The company can choose to use the resistance test when investigating instances of product failure.” Where resistance is confirmed, Dr Levot says alternative control options are available. However, he notes that the most common fallback treatment – dipping in the organophosphate, diazinon – is subject to a suspension order from the Australian Pesticides and Veterinary Medicines Authority (APVMA), due to occupational health and safety concerns. “Although existing stocks of diazinon products purchased prior to the May 2007 suspension may be used according to their label instructions, product manufactured after that date cannot be used for dipping or jetting sheep. DR GARRy Levot is ceRtAin thAt viAbLe Lice contRoL options cuRRentLy exist AnD thAt moRe tooLs ARe on the wAy. in the meAntime, he emphAsises thAt benefits fRom existinG Lice contRoL effoRts cAn be mAximiseD by impRovinG on-fARm biosecuRity. “Fortunately, the suspension order created an incentive for chemical companies to develop alternatives.” Already launched onto the market are wet dips based on two new active ingredients: l temephos – a low-toxicity organophosphate marketed under the name Assassin®; and l spinosad – a low-toxicity and low-residue ‘organic’ product (now also available as a backline) marketed under the name Extinosad®. To prevent chemical resistance becoming more common, Dr Levot warns against over-reliance on any one class of chemical, and advocates the adoption of a simple, two-step prevention strategy: l only use a treatment when absolutely necessary; and l if the need arises to treat the same sheep in short and long wool – even if targeting different pests – choose chemicals from different classes. He acknowledges the difficulty of avoiding unnecessary chemical treatment, given the lack of a simple lice detection test. Although there has been interest in developing a test for the past 12 years, the project has recently received a new round of funding from AWI. To date, Dr Levot’s group has developed an immuno-diagnostic test capable of detecting louse protein in the debris that accumulates on shearers’ combs and cutters. The test requires specialist laboratory staff and a day to complete upon receipt of samples. It is based on antibodies developed jointly with CSIRO Livestock Industries, and is nearly ready for a pilot validation trial. The more recent AWI project aims to convert the laboratory test to a simple kit for use in the shearing shed. The current test is capable of detecting as few as 10 lice per sheep, and will undergo on-farm testing in several districts with the cooperation of interested woolgrowers. Since the project was unable to attract a commercial partner to produce user-friendly kits, the NSW DPI has agreed to undertake this role. Overall, Dr Levot is certain that viable lice control options currently exist and that more tools are on the way. In the meantime, he emphasises that benefits from existing lice control efforts can be maximised by improving on-farm biosecurity, especially by ensuring that fences are sheep-proof and that new animals are quarantined on-farm for at least 20 weeks. Dr Schröder says the range of lice control options, benefits, risks and costs can be previewed and assessed using a free, decision-support tool developed for AWI, called LiceBoss™ (www.liceboss.com.au). The software is designed to assist with lice management issues, and draws on a compilation of best-practice information about lice treatment. More information: LiceBoss, www.liceboss.com.au; Dr Garry Levot, email@example.com ú
February March 2009
Oct - Nov 08