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Friday, 3 August, 2001, 21:02 GMT 22:02 UK
Foot-and-mouth vaccine 'little help'
Pig and anti-slaughter poster PA
The slaughter policy was unpopular, but the study suggests it was right
By BBC News Online's environment correspondent Alex Kirby

A computer model of strategies for controlling the UK foot-and-mouth outbreak suggests mass slaughter is the best way.

The model found that vaccinating animals in the worst-affected areas could have helped only marginally.

At worst, it says, replacing slaughter with vaccination in buffer zones would have let the outbreak spread out of control.

The model appears to vindicate the government's persistence in slaughtering animals to end the outbreak.

The results of the modelling are reported in the Veterinary Record, the journal of the British Veterinary Association.

The modelling assumed the control policies which were in operation from 20 March - a ban on all animal movements from 23 February, and a policy of stamping out the disease by slaughter.

The outbreak was confirmed on 20 February, and the veterinary surgeons and epidemiologists who wrote the report say: "The epidemic was already well established and disseminated by the time it was diagnosed.

"Epidemiological data show that at least 29 farms were infected but undiagnosed at the date of the initial confirmation."

Close prediction

They simulated a number of control strategies, starting with the known number of infected farms on 10 April, and running for 200 days.

They write: "For the control policy which best approximated that actually implemented from late March, the model predicted an epidemic of approximately 1,800 to 1,900 farms.

"It estimated that the epidemic would be eradicated between July and October 2001, with a low probability of continuing beyond October.

Sheep grazing AP
Sheep movements spread the virus
"This policy included the slaughter-out of infected farms within 24 hours, slaughter of about 1.3 of the surrounding farms per infected farm within a further 48 hours, and minimal inter-farm movements of susceptible animals."

By 3 August the total number of cases across the UK had reached 1,925.

The modelling showed that delays in the slaughter of animals on infected farms beyond 24 hours after diagnosis slightly increased the size of the epidemic.

But failure to slaughter pre-emptively on an "adequate" number of at-risk farms substantially increased its expected size.

With vaccination, the modellers considered two possibilities. One was the vaccination of three of the most seriously affected areas, in Cumbria, Devon and Gloucestershire.

Barrier vaccination

Using vaccination here with the control policy that was in force would have reduced the predicted size of the epidemic by fewer than 100 farms, they say.

The other possibility tested was the use of "buffer zone" vaccination in a series of bands across the country, designed to create a barrier between affected and disease-free areas.

Cattle and pyre AP
Vaccination could have helped marginally
It allowed the disease to spread out of control, predicting by October an epidemic three times larger than the existing one, with more than 6,000 farms affected, and "with no prospect of immediate eradication".

The authors conclude: "The analyses support historical field experience in reinforcing the crucial value of the slaughter of all susceptible animals on affected farms as rapidly as possible after diagnosis, and especially the benefits of pre-emptive slaughter of high-risk farms before signs of disease can appear."

Spread by sheep

One of the report's authors is Professor John Wilesmith, of the London School of Hygiene and Tropical Medicine.

He told BBC News Online: "It's still possible that vaccination might be of value in certain circumstances.

"The Dutch used it successfully, but theirs was a totally different scenario.

"They were able to identify where it was needed, go to the fridge and start vaccinating.

"We were up against it from the very beginning, because of the early movements of sheep which spread the virus across the country."

The BBC's environment correspondent Tim Hirsch
"The findings are likely to be challenged"
See also:

02 Jul 01 | Sci/Tech
Farming 'facing massive job losses'
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