Alternative methods for the control of sheep scab.

For nearly 17 years, plunge dipping has been the only method of scab control in the UK under a Government-controlled eradication campaign. Dipping is inconvenient and has been incriminated in the post-dipping illness of stockowners and contractors, and the disposal of large volumes of used dipwash is a potential hazard to the environment. Upon the deregulation of sheep scab in July 1992, stockowners are no longer obliged to dip and will seek alternative methods of scab control, ie, systemic injectables or synthetic pyrethroid pour-ons. Plunge dipping still offers the only fully effective method of controlling scab and it has a broad spectrum of activity against other ectoparasites of sheep. The present systemic pour-ons and oral drenches have little effect against scab, but double injections of systemic acaricides, ie, ivermectin, show great promise. The efficacy of systemic injectables is related to the initial mite burden and the second injection must not be omitted if complete control is to be achieved. The available synthetic pyrethroid pour-ons do not cover the entire sheep with a standard dose of acaricide, and leave the ventral surfaces unprotected and the sheep open to reinfestation.