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Professor Bostock has passed your enquiry about FMD tests on to me.

Improvement of the tests for FMD is an ongoing activity at Pirbright, which is the World reference Laboratory for FMD. Recent developments have been the first "pen-side" detection system and a lab based alternative to virus isolation in cell culture.

Up till now, animals suspected of having clinical FMD have been tested by sending samples down to Pirbright. These samples are examined for the presence of the virus by an antigen detection ELISA and by virus isolation in cell culture. The former is a quick test taking around 4 hours. Positive ELISA results are very reliable, but negative ones must be confirmed by virus isolation since ELISA may miss 10-20 % of positive cases where there is only little virus present. Virus isolation involves growing the virus in vitro and is very sensitive, but time consuming. Four days must be allowed before the sample can be signed off as negative.

In collaboration with colleagues in Sweden, we have developed a "pen-side" version of the antigen ELISA that can be performed in the field - "next to the pen of the animal". The test is similar in appearance to a pregnancy test kit and a small amount of test sample is prepared and applied to a chromatographic paper impregnated with reagents (known as a lateral flow device). After 10 minutes to allow for the materials to diffuse out, a result is read by looking for the appearance of a reaction line in the window of the test kit. The pen-side test appears to have similar sensitivity to the lab-based antigen ELISA test.

Secondly, we have developed a polymerase chain reaction (PCR) test to amplify the viral nucleic acid in the lab. This technology is widely used in veterinary, medical and forensic science. The method has similar sensitivity to virus isolation but can be performed within one day. The main weakness is the need for multiple preparation steps in extracting the nucleic acid from the sample prior to testing. This can be overcome in the laboratory by the use of a robot which can process multiple samples at once without leading to sample cross-contamination.

Both of these tests could contribute to more rapid diagnosis of clinical cases. For field use, veterinarians would need appropriate training in test performance and a system of quality control would be required to ensure the reliability of results.

The Cephaid smart cycler is a compact version of a PCR machine. It has been assessed in the lab at Pirbright and found to give satisfactory results, provided that our reagents and protocols were followed. It is not so easy to carry out PCR testing as a pen-side activity due to the need for the sample to be processed so as to extract the nucleic acid. If this processing is omitted then the sensitivity of the system is greatly reduced and the test has no advantage over the simpler antigen-based pen-side test described above. Conceivably testing could be done in mobile laboratories located closer to affected farms.

David Paton

Dr David Paton
Head, Department for Exotic Disease Control
Pirbright Laboratory
Institute for Animal Health
Ash Road
Pirbright
Surrey GU24 0NF
UK
Tel +44 1483 231012
Fax +44 1483 232621

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