The enzyme linked immunosorbent assay (ELISA) test, frequently used to test HIV and now foot and mouth disease (FMD), is notoriously unreliable. The test is conducted using a sample of the patient's blood, which is added to a mixture of proteins. It is assumed that if antibodies to the FMD virus are present in the sample, they will react to the FMD present. The problem is that the ELISA test also shows reactions to the antibody proteins caused by other diseases.

Take the case of HIV. The protein p24, which is accepted to be proof of the existence of HIV, is found in all retroviruses that live in the body and do no harm. In addition, malaria, hepatitis B and C, papillomavirus warts, glandular fever, syphilis, tuberculosis and leprosy are just a few of the conditions capable of producing biological false positives in ELISA (Nature, 1985; 317: 395-403).In one study, antibodies to p24 could be detected in one out of 150 healthy individuals, 13 per cent of randomly selected healthy people with generalised papillomavirus warts, 24 per cent of patients with T-cell lymphoma and 41 per cent of those with multiple sclerosis (N Engl J Med, 1988; 318: 448-9).

In another study in 1991, half the patients who had tested positive on an ELISA test later tested negative. The study concluded that ELISA is "clinically erratic and should be interpreted cautiously" (Abstracts, VIIth International Conference on AIDS, Florence, Italy, 1991; 1: 326). In Russia, out of 20,000 ELISA tests which were positive for HIV, only 112 were confirmed positive on a second testing.

In truth, any humans or animals exposed to a greater than normal amount of disease would be likely to have a false positive ELISA test.