SHORT-TERM WAYS OF FIGHTING CLA
Caseous lymphadentitis is a growing threat to the UK sheep
industry and for this reason a vaccine is swiftly being sought.
In the meantime James Garner looks at what flock-owners
need to know to avoid or control infection in their flocks
OPENNESS from sheep breeders countrywide would help the UK stop caseous lymphadentitis (CLA) from becoming a bigger threat to the UK sheep population.
In the immediate term there is no available vaccine or blood test to help control the disease, and it is likely to remain this way for at least another 18 months.
According to Anne Jones, managing director of Leeds Veterinary Laboratories, there is an urgent need for a vaccine. There is no other method of CLA control and infected flocks are taking few precautions against spreading it, she adds.
"The number of cases is bound to increase because of the way we trade and mix sheep in this country; and as treatment is ineffective, prevention has to be a better method of control."
CLA will continue to be a threat while infected flocks continue selling sheep. This, although based on hearsay, indicates many flock owners havent taken the disease seriously enough, she says
"You hear some reports of flocks being sold up but, because of the chronic nature of the disease, where 10% of sheep are infected, a dispersal sale will only serve to spread the disease."
In extremely serious cases the Leeds Veterinary Laboratories tailor-make vaccines for CLA on an individual farm basis. But Mrs Jones says a widely available vaccine is required in the UK to stop CLA becoming more of a problem.
According to SAC St Boswells vet Graham Baird, a vaccine is being put forward to the Veterinary Medicines Directorate for licensing, but this takes time.
Nevertheless, based on work done in Australia, a vaccine could make its way on the market within two years, which would then provide breeders with a way of controlling CLA.
"In that time its important that breeders and commercial producers do all they can to keep on top of this disease until we have the tools, such as a vaccine or blood test to control it," says Mr Baird.
But do recent statistics suggesting that the disease is on the rise with about 50 infected flocks last year, underestimate the scale of the problem because of under-reporting?
"The perception is there is a fair degree of under-reporting," says Mr Baird. However, he reckons the disease is still fairly uncommon, even though VIC centre data indicates a rapid increase recently.
Under-reporting remains the battle ground in trying to contain CLA, as Mr Baird explains. Pedigree breeders have the most to lose from reporting the disease as it means losing sales.
Therefore, he advises both breeders who havent seen CLA in their flocks, and commercial ram buyers, not to buy it in.
"But when buying check breeding stock for lumps or discharging abscesses, particularly around the jawline, and dont buy stock youre unsure of."
This is not the only risk though, as it can cause abscesses in the lungs; in this scenario it is transferred by aerosol particles and anyone buying stock infected in this manner, has little chance of spotting them and it is these that pose the biggest concern, admits Mr Baird.
In theory buying a ram could bring the disease in to close contact with 40 or 50 ewes during tupping and give it a foothold in your flock, says Mrs Jones.
Although it may be easy to introduce into your flock, research work seems to suggest it spreads through the flock more sedately, normally taking two to three years to become really established in a flock. This slow spread may mean that more sheep have the disease than presently thought.
However, there is some reassurance in this fact, explains independent sheep vet Chris Lewis. "Mixing youngstock with old stock seems to increase the spread within the flock. So dont mix them."
Young then old
As for flock management, if you have an infected flock, he says it may be worth gathering young sheep first and then older sheep. Similarly, he says that care should be taken with mixing ram lambs with shearlings or older stock rams, particularly when trough feeding. This is a time when the disease can easily spread, he adds.
Any infected animals should be isolated until they are free of the disease, says Mr Baird, although in practice most CLA positives are culled out of the flock to prevent further infections. He also warns against lancing any suspicious lumps, because this is likely to spread the infection further.
Ideally, he reckons the best policy is to run a clean and dirty flock, when there is enough space, he adds.
• CLA on the increase.
• Report infections.
• Be vigilant when buying-in stock.
Symptoms – It is a chronic disease of sheep and goats, characterised by the formation of nodules containing a cheesy pus occurring in the lymph nodes, lungs, skin, or other organs; exhibiting a tendency to produce a chronic pneumonia or pleurisy.
Occasional cases occur in Britain, mostly as chronic abscesses under the skin, but sometimes involving the lung or other internal organs.
Treatment – This is difficult as the lesions become encapsulated and so inaccessible to antibiotics. Veterinary advice should be sought.
Source: Blacks Veterinary Dictionary