At least 850 suspect cows are being sought by Ministry of Agriculture officials, who fear that some may still harbour the virus even though they have been in the country for months.
Farmers face immediate losses of about pounds 1m if the ministry decides the imported cattle must be slaughtered, and much greater losses if an epidemic breaks out. The policy of eliminating the disease from Britain is considered absolutely necessary because of the drastic economic effects if it is allowed to run freely - the killing of infected animals and reduced breeding performance.
The animals, mostly Holstein heifers, were given false papers by central European dealers, who are thought to have made large profits in hard currency. Britain and the European Community have now banned the trade but government vets are still testing the suspect heifers.
Since last August, about 450 Holsteins have been imported from the Czech and Slovak republics and another 400 from Poland. The animals were not thought to be a problem until foot and mouth disease broke out in Italy and is believed to have originated in cattle imported from Croatia or the Czech and Slovak republics. But imports from all eastern European countries are now being treated with suspicion.
The illegal imports into Britain came to light when Ministry of Agriculture scientists, who were testing blood samples for bovine leucosis virus, made extra tests for foot and mouth disease antibodies. After some tests proved positive, more extensive tests were made on the imported heifers, which found that some 200 had been vaccinated against foot and mouth disease. However, no clinical signs of disease in the animals or their contacts has been found.
The suspect heifers were imported in 27 consignments and split up in sales at various markets. Six consignments comprising 129 animals went to Scotland. The animals are understood to have had false certificates stating that they were unvaccinated.
Ministry officials have concentrated on tracing animals imported from the Czech and Slovak republics because positive tests have been found in these animals. No positives have yet been found among cattle imported from Poland but they will be checked.
For many years Britain has banned the import of animals vaccinated against foot and mouth disease because they may carry the infection, a policy recently adopted by the EC. But veterinary scientists differ over how long vaccinated cows may carry the foot and mouth virus and still remain infectious.
Francis Anthony, president of the British Veterinary Association, said: 'It is theoretically possible for a vaccinated animal to carry the virus in its tonsils but it is not known in practice. The incubation period of foot and mouth is 8 to 10 days - if an animal has not developed the disease in 21 days you can assume it is not going to do so. These imported animals have been mixing freely with unvaccinated stock and so the disease would be expected to have manifested itself by now in most cases if it was going to.'
On the basis of this opinion, cows which have been in Britain since August may be assumed to be free of the disease. However, Ministry of Agriculture experts take the view that vaccinated cows may harbour the foot and mouth virus for many months without any manifestation of disease and without shedding infectious viruses. The disease might manifest itself suddenly in a herd that has harboured an imported cow for months.
The ministry has restricted the movement of the suspect animals and will decide in the next few days whether they will have to be slaughtered or re-exported. Either policy would involve a large financial loss for farmers. The ministry believes that it will not be legally liable to compensate farmers because the animals were imported illegally.Reuse content