Tuesday 10 April 2001, p. 6,
by Steve Connor and Nigel Morris.
FARMERS WERE urged by the Government yesterday to take more care over the spread of foot-and-mouth disease because of fears that the virus was reaching new areas by human transmission.
The warning came as the Ministry of Agriculture, Fisheries and Food (Maff) said a vehicle carrying supplies between farms was the most likely cause of an outbreak near Whitby in Yorkshire, which is about 40 miles from the nearest affected area.
A Downing Street spokesman said yesterday: "We all have a stake in this. Some of these isolated outbreaks over the weekend have been identified as farm-to-farm transmission."
He said farmers could have spread the infection "unthinkingly and inadvertently" and added: "We want to send out a very strong signal to the farming community. If you have to make journeys make sure to disinfect footwear and vehicles. And disinfection is far more effective if you use clean vehicles."
A ministry spokeswoman said that in the Yorkshire case airborne transmission was unlikely to have resulted in the virus leapfrogging over the culling ‘firewall’ that is intended to prevent the disease spreading from areas known to be contaminated into the wider countryside.
The spokeswoman said: "Whenever we have an infected premise, we try to trace the movements in and out of that farm. The most likely route in this case is vehicle movement but this has not been confirmed."
The Government’s chief veterinary officer, Jim Scudamore, and its chief scientific adviser, Professor David King, have both said airborne transmission of the virus can occur under certain circumstances.
Pigs are a special risk because they are known to be "virus factories" that can pump out up to a thousand times the amount of virus produced by other species of farm animal such as sheep. They are the cause of so-called pig plumes – large volumes of floating virus that are carried many miles by the wind.
Cattle and sheep are especially susceptible to being infected by the virus by inhalation, whereas pigs tend to pick up the infection by eating contaminated food. However, all pigs that have been infected during the current outbreak have been slaughtered.
Scientists at the American government's Plum Island Animal Disease Center in New York state carried out airborne transmission experiments on pigs and found that the virus could not be transmitted between members of a swine herd by air currents alone. Fred Brown, an authority on the virus at Plum Island, said the experiment was repeated six times but failed to uncover any evidence for airborne transmission between pigs.
In the American experiment, a group of pigs infected with foot-and-mouth were put in the same barn with an uninfected group, separated by a barrier to prevent physical contact. Although both herds breathed the same air, the uninfected group remained free of the disease. Dr Brown said:"They did this seven times but none of the uninfected pigs came down with foot-and-mouth."
Chris Bostock, director of the Institute of Animal Health, said there was abundant experimental evidence to show that airborne transmission was a real threat, especially when pigs and cattle were involved.
Epidemiologists, for instance, were able in 1981 to predict correctly than an outbreak of foot-and-mouth among pigs in northern France posed a risk to animals in Jersey and the Isle of Wight because of prevailing northerly winds, Professor Bostock said.
However, Dr Brown is sceptical that wind was the transmission route. He said: "I find it difficult to accept that the virus could have travelled 170 miles through the air. There is no direct, physical evidence for airborne transmission of foot-and-mouth virus."