Comparisons of original laboratory results and retrospective analysis by real-time reverse transcriptase-PCR of virological samples collected from confirmed cases of foot-and-mouth disease in the UK in 2001

September 27, 2006 — N. P. Ferris, BA, MSc, PhD, D. P. King, BSc, PhD, S. M. Reid, BSc, MSc, A. E. Shaw, BSc and G. H. Hutchings, MIBiol

There were 2030 designated cases of foot-and-mouth disease (FMD) during the course of the epidemic in the UK in 2001 (including four from Northern Ireland). Samples from 1720 of the infected premises (IPs) were received in the laboratory and examined for either the presence of FMD virus (virological samples from 1421 IPs) or both FMD virus and antibody (virological and serological samples from 255 IPs) or antibody alone (from 44 IPs). The time taken to issue final diagnostic results ranged from a few hours in cases in which positive results were obtained by ELISA on epithelia containing sufficient virus to be detected, to several days for samples containing small amounts of virus requiring amplification through cell culture, negative samples or samples tested for antibody.

Two subsets of samples were analysed retrospectively by real-time reverse transcriptase-PCR (RT-PCR); first, epithelia that were negative by both ELISA and virus isolation (VI) in cell culture, and secondly, samples that were negative by ELISA on epithelial suspension but positive by VI. There was broad agreement between the RT-PCR and VI/ELISA combined, except that the RT-PCR procedure did not detect a group of related virus isolates from Wales. These viruses had evidently evolved during the epidemic and had a nucleotide substitution in the RT-PCR probe site, which prevented them from being detected by the routine diagnostic probe.

No evidence of FMD virus, antibody or nucleic acid was found in approximately 23 per cent (390 of 1730) of IPs from which samples were received, suggesting that the incidence of FMD during the outbreak may have been over-reported.

The Veterinary Record 159:373-378 (2006)
© 2006 British Veterinary Association

[Ed. This study illustrates the need for the validation of "real-time" animal-side diagnostics that can aid in the determination of disease status for foreign animal diseases in all susceptible species. Such rapid diagnostic tests have been developed for some diseases in some species by researchers at Plum Island but are in need of on-going validation requiring real world testing in countries currently experiencing outbreaks of these diseases. In most cases, the designation of "Infected Premises" during the 2001 FMD outbreak in the UK was made based on the presence of clinical signs suggestive of FMD infection. This was a very subjective assessment that was potentially flawed for a number of reasons such as the unfamiliarity of the investigator with the lesions associated with FMD or the animals being examined, the presence of ulcerations resulting from other disease conditions (such as Orf, which was rampant during the time of the outbreak) or the consumption of abrasive materials such as thistles, briars or twigs (which was common due to the quarantining of animals on over-grazed pasture), and the desire to prevent the spread of the disease which resulted in decisions erring on the side of added caution. An animal-side test would have been a welcome addition to the diagnostic efforts of the investigators in the field.]

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N. P. Ferris, BA, MSc, PhD, D. P. King, BSc, PhD, S. M. Reid, BSc, MSc, A. E. Shaw, BSc and G. H. Hutchings, MIBiol Department of Vesicular Disease Control, Pirbright Laboratory, Institute for Animal Health, Ash Road, Woking, Surrey GU24 0NF