21 July 1995

Super-scab on the horizon, UKsheep industry is warned

SHEEP scab resistant to all chemical control, including organophosphorus dips, could emerge in the UK, warns MAFFs former head of parasitology at the Central Veterinary Laboratory, Dr Gerald Coles.

"I think we could find within a short period of time – one to three years – that we could have scab for which there is no chemical left to control it," said Dr Coles, senior research fellow at Bristol University. "I hope I am proved wrong."

Circumstantial evidence already exists that OP-resistant lice may be present in the UK flock and that pyrethroid-resistant lice are likely to develop. Blowfly resistance has not yet been reported, but it is common in Australia and New Zealand.

"I have not heard of it reported in this country, but that doesnt mean it doesnt exist," said Dr Coles. "I think we have just been very lucky in this country. There is no reason why it cant happen."

He added that, in his experience, farmers do not usually report drug failure to their vets and so to MAFF. A green card reporting scheme for "adverse reactions" to veterinary medicines is run by the Veterinary Medicines Directorate. But Dr Coles said the system was not being used significantly for anthelmintic resistance.

A CVL survey in 1990 found benzimidazole-resistant nematodes in 60% of West Sussex sheep flocks. But there were very few reports sent to the VMD.

Pharmaceutical companies are also reluctant to investigate resistance. "If they are going around looking for resistance to their products they are not doing themselves any good," said Dr Coles.

He added that there was also good reason to believe that pyrethroid scab mite resistance was more widespread than the two cases reported recently by vets.

MAFF maintains animal health is "the industrys" responsibility. But Dr Coles said the only way to deal with resistance in scab and lice is to eradicate these ectoparasites while effective drugs exist. "I dont know of any other way," he added.

"If you are dealing with infectious disease that is changing you have got to have a battle plan." That would involve a sheep health scheme, using correct treatment where outbreaks occurred. Without such a scheme "we are going to pay a high price very shortly".