21 May 1999
Action needed on sheep disease CLA
By James Garner
INCREASING numbers of sheep are being infected with Caseous lymphadenitis (CLA), meaning risk of spreading the abscess-causing infection is rising.
Producers are urged to take precautions to halt its spread, while two research projects hope to find out more about the disease.
In the UK, the number of reported cases of CLA has risen from just six flocks experiencing an outbreak in 1996, to 62 flocks in 1998, a tenfold increase, according to official disease statistics.
But vets and researchers reckon there is considerable under-reporting of the condition and more cases than this exist
CLA is one of the worlds most important sheep diseases in terms of economic loss, and is in the top three in both America and Australia, where its abscesses cause carcass downgrading.
Infection is spread via pus from abscesses or by aerosol means, says Bristol Universitys Laura Green.
“The pus, excreted from abscesses 2-3cm in diameter, is infectious for a long time, up to eight months. It looks like cream cheese, but does not smell.
“Abscesses are often located below the ears along the hairline. These can move to the lungs and can then be transferred by infected animals coughing stuff up and spreading the disease.”
Despite being an increasing concern, there is much about the disease that remains unknown to UK vets. But its trends offer some clues, says SAC St Boswells vet Graham Baird.
“It is appears that terminal sire breeds are worst affected. The worry is that this could spread CLA around the country more quickly because rams are more frequently sold or loaned between flocks.”
He warns producers and breeders to be extra vigilant when buying flock replacements.
“In general it is best to prevent buying-in the disease, so try to identify animals with CLA before mixing them with your flock.
“This means checking for lumps around the head and neck, which is where most abscesses occur.”
When a lump is found, keep the animal in quarantine until your vet has diagnosed it, he adds.
Part of the difficulty in dealing with the disease is the lack of a diagnostic test to tell which sheep are infected or carrying CLA. Two research projects, at SAC and Bristol University, are trying to establish a diagnostic blood test.
Dr Green – who is heading up the Bristol project – says they hope to discover the extent of CLA, develop a diagnostic test, establish how it is passed on and find out how important it is for the UKs sheep economy.
Despite indications suggesting that buying-in CLA remains the biggest threat to clean flocks there are other areas of concern. “It could be spread by shearers or other contract operations.
“If an abscess bursts, clear up the pus and dispose of it in a dustbin. Then disinfect the whole area thoroughly,” she advises.
Oxon sheep vet Chris Trower agrees, but says it is difficult to persuade shearers to disinfect their equipment because this means exposing combs and cutters to water which contractors are loath to do.
But shearing is a good time to spot lumps, and he suggests the best action is to cull animals discovered to be carrying CLA.