8 September 2007

2 minute read

Executive Summary

1. The virus strain, type O1BFS, that caused the outbreak of Foot and Mouth Disease (FMD) in Surrey in August 2007 has been shown beyond reasonable doubt to originate from the nearby Pirbright site where a commercial vaccine production plant and a research and diagnostic laboratory are co-located.
   
   
2. The estimated period during which the first infected premises (IP1) was infected with FMD virus is most likely between 12 - 25 July, as determined from examination of the animals at slaughter.
   
   
3. This likely period of infection was foreshortened to 19 -25 July, following the characterisation of the virus isolated from IP1 as the O1 BFS type. This strain was not handled in any quantity by either facility on the Pirbright site during the originally identified period until the week beginning 16 July. Subsequent investigations supported these assumptions and revealed no need to revert to the original, clinically derived infection period.
   
   
4. We have considered windborne transmission of aerosolised virus from the site to IP1. Expert investigations of the HEPA filtration systems, commissioned by the HSE investigation team, revealed no evidence of a breach of these systems. Although there is circumstantial evidence for such transmission from the site it is unlikely that there was a release of aerosilised virus to effect a transmission from the site to IP1.
   
   
5. Investigations indicate that release was most likely due to escape of live virus from the drainage system that connects the vaccine production plant to the sodium hydroxide treatment tanks on another part of the Pirbright site. Movement of the virus off site was most likely from movement of fomites created from soil, water or other material contaminated by effluent, and deposited on the road from which the track to IP1 leads.
   
   
6. Using the EFSA definitions of risk, the probability that live virus is present in the external environment on the Pirbright site or elsewhere, and could be transmitted to susceptible stock, is very low (i.e. this outcome is very rare but cannot be excluded). This risk is further mitigated by biosecurity measures in place on site and the remaining surveillance work.
   
   
7. Figure 1 in this report shows a diagram of the ‘timeline’ to show the temporal relationship of the key events reported.

Further Reading

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