29 May 1998

Strict hygiene vital to restricting spread

SAFEGUARDING flocks against Caseous lymphadenitis means taking precautions, particularly at shearing and dipping and with infected animals.

Any sheep which is suspected to be carrying CLA should be isolated from the flock, stresses Brian Preece, head of Starcross vet investigation centre, Exmouth, Devon.

"It is difficult to give specific advice, but with commercial animals, isolate them when they are discharging pus from abscesses to limit infection spread. Keep them isolated until the discharge disappears, then always handle them last to reduce risks.

"Good hygiene is vital, so keep everything clean. The organism causing CLA can survive for up to two months on straw, so ensure careful disposal of bedding where there are infected animals, and preferably clean all equipment between animals."

At clipping, all contract shearers, labour and equipment should be disinfected before coming on the farm, says Dr Preece. "The organism causing CLA can survive on clothing and equipment, so cleanliness is vital. Disinfect using any MAFF approved product."

The greatest risk of infection spread comes from aerosol spray when shearing, dipping or spraying and the organism enters sheep through cuts or wet skin.

"Researchers in Australia have found that CLA bacteria survive for up to 24 hours in dips, and that it can enter animals through damp skin. Dress any shearing cuts as soon as possible, and wait at least a fortnight between clipping and dipping to ensure all skin wounds have healed."

Reduce risk of buying-in infection by careful examination of any potential flock purchases, particularly rams. Tups are more likely to spread infection by fighting with one another, so look for evidence of scarring round the head, he says.

"After purchase, isolate animals for two to three weeks before introducing them into the flock. Although it can take three to four months for lesions to develop it is obviously impractical to isolate sheep for that length of time. Isolation for a shorter period will at least help reduce risks."

People handling infected sheep should also ensure good personal hygiene, he says. "Although CLA is not really regarded as a zoonosis there are a few cases of it occurring in humans in Australia where lymph glands become filled with pus. There are no cases reported in the UK, but personal hygiene is obviously important." &#42

REDUCING INFECTION RISK

&#8226 Isolate infected and bought-in animals.

&#8226 Good flock and personal hygiene.

&#8226 Wait 14 days between clipping and dipping.