Johnes disease is on rise

26 April 2002




Johnes disease is on rise

By Marianne Curtis

JOHNES disease is on the increase, according to recent reports in Vet Record, but vets are divided over whether the increase is genuine or due to higher awareness, leading to more frequent reporting of cases.

Vet Record reports a rising trend in diagnoses of Johnes over the past 10 years in England and Wales. In Scotland, the number of outbreaks a year has risen from about 200 in the early 1990s to 400 since the mid-1990s and more than 100 cases have been reported so far this year.

Head of SACs vet science division Alastair Greig estimates the average cost of Johnes in infected herds is £26 a cow a year for dairy and £16 a cow a year for beef herds. He says although case numbers have remained similar over the past few years, the cattle population has fallen, suggesting the disease is increasing.

"We are seeing a geographical spread. Johnes hotspots used to be in northern Scotland and on the east coast, but we are now seeing cases in the western isles and south-west Scotland."

Lack of care when buying stock is partly to blame and restocking may have exacerbated the problem, he says. "Buying in animals from herds which are members of cattle health schemes is sensible. When restocking, there is a temptation to buy cheap beasts rather than have an empty farm. But this can spread diseases, including TB, to new areas."

While many problems remain to be solved about how the disease spreads and why certain animals contract Johnes and others do not, Kenton Morgan, researcher at Liverpool Vet School, is sceptical about reports that the disease is increasing. "In the mid-1990s, we carried out the first study since the 1950s on incidence of Johnes disease and found little change over the period.

"The only handle we have on it is from reports on submissions to vet labs. But labs ability to diagnose the disease has improved. In addition, there is potential to tackle it through cattle health schemes, whereas in the past there was no option but to slaughter diseased animals. These factors, together with increased interest in Johnes disease mean more samples have been submitted to labs, giving the impression that it is an increasing problem. But there is no evidence that it is."

But Peter Orpin of Leics-based Park Vet Group, is convinced that modern farming methods have led to an rise in Johnes disease. About 10% of his clients have identified it in the past three years and he estimates it can cost infected dairy herds 0.5p/litre a year through extra culls and lost milk.

"We thought this disease was dead and buried, but there has been a resurgence. There is potential to miss it, as producers may cull a cow which loses weight, scours and has a low yield without seeking a diagnosis, but such a cow could have Johnes."

Increasing herd size, which can lead to overcrowding and pressure on calving areas are contributing factors, says Mr Orpin. "Although clinical signs of Johnes disease can take five years to occur, infection happens during the first month of birth from contaminated faeces, colostrum or milk.

"Improving hygiene of calving areas and avoiding feeding pooled colostrum and milk reduces the likelihood of infection. Also try to buy in clean stock.

"In the US, which has an even more intensive dairy industry than the UK, 40% of the national dairy herd is infected with Johnes. So, as the industry intensifies, it is likely to become more of a problem." &#42

JOHNES DISEASE

&#8226 Increasing incidence?

&#8226 Buy clean stock.

&#8226 Risk for intensive farms.


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