September 12, 2007

Not a good day

DEFRA has confirmed what nobody wanted to hear – foot and mouth has struck in Surrey again. The BBC were reporting it a while before the official announcement came, but I guess they have better spies than I do!

The new case is about 10 miles from Pirbright, some distance from the cases we saw in August. The strain is, as yet, unknown, but I think the assumption until proven otherwise must be that this will be the same O1 BFS67 strain that leaked from the Pirbright site to cause the earlier outbreak. The HSE’s final report into biosecurity at Pirbright makes for uncomfortable reading – while we will never know which of the three facilities on-site leaked the virus, it seems that there were several significant failings in the category 4 biosecurity arrangements on that site which combined with heavy flooding to cause the outbreak.

What’s got me scratching my head is the time-lag before this outbreak; indeed, when I heard this morning there was a suspect case, I was assuming it would turn out not to be confirmed. FMDV (the virus that causes foot and mouth) doesn’t survive for long in the environment, so why has this case appeared now, given the last infected animals were culled on the 9th of August? The OIE’s handy summary gives 14 days as the upper end of the incubation period. It can survive in the environment if conditions are suitable for up to a month, but the previous infectious premises will have been rigorously disinfected.

I think that means that direct transmission from the August infectious premises is fairly unlikely to be the cause of this outbreak. I can’t find another more plausible hypothesis, though; did more contaminated soil leave Pirbright during the recent past (surely not, biosecurity was substantially tightened up during the HSE investigation)? are there other infectious animals out there that we haven’t spotted (again, this new case is only just outside the old surveillance zone, so animals nearby would have been inspected regularly)? Even if it is direct transmission from the previous infected farms, how did the virus escape disinfection? At this stage, we will have to wait and see. Easier to do as an epidemiologist than as a farmer, trying to get back on track after the previous round of movement restrictions…


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