Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5805152 | Veterinary Parasitology | 2012 | 5 Pages |
A retrospective study in which the 18Â years treatment history of a mob of sheep hosting a pyrethroid resistant strain of sheep body lice was compared with the coincidental changes in that strain's response to cypermethrin, provided a unique opportunity to investigate the stability of pyrethroid resistance in this species. Resistance levels remained very high (resistance factors (RF)Â =Â 75-145) for at least five years following the cessation of pyrethroid treatments but within ten years had dropped to only 5, a level similar to many normal field strains and certainly not indicative of high-level resistance. Resumption of pyrethroid treatment of sheep infested with these lice caused a coincidental increase in resistance to an extreme level (RFÂ =Â 321) within two years. Wool producers considering a return to pyrethroid use to control louse infestations should be aware that such a strategy may not be sustainable in the long term and that in Australia effective registered alternative treatments are available.