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Foot and mouth disease went un-noticed for almost a month at the site of the fifth case of the disease which allowed it to spread to two neighbouring farms, a DEFRA investigation has concluded.
The second epidemiology report of the 2007 outbreak published by DEFRA on Monday (24 September) considers how the disease came to be present on three further premises between 12-18 September. It does not therefore consider how the disease might have spread to the two most recent cases, outbreaks six and seven.
Infected Premises 5, as it is described, was a small holding consisting of 22 beef cattle, 16 sheep and two pigs located 16km (10 miles) north of Pirbright.
The disease was identified by the first Protection Zone visit, when although clinical inspection revealed no evidence of the disease, all 12 of the sheep sampled on the 17 September returned positive results to the serological tests.
According to DEFRA this indicates that these sheep had been infected for at least eight days.
At this point all susceptible animals on the holding were slaughtered. Clinical examination of 17 of the 22 cattle and 10 of the 16 sheep had healing lesions and scars in the mouth and on the feet.
According to one of the Institute of Animal Health’s experts the oldest lesion in the sheep was two to three weeks old, and that in the cattle to be four weeks old.
Had infection been detected earlier it might have prevented the disease from spreading to infected premises three and four, says DEFRA.
“Epidemiological evidence to date suggests IP5 was infected first and most likely transmitted infection to IP4. IP3 may have been infected by either IP4 or IP5.
“These additional IPs would have been prevented by the early detection and notification of suspect FMD on IP5, but clinical disease was not detected or reported.” (See diagram at bottom.)
The investigation also considered how the disease spread to infect the farm 20km north of the two premises infected in August. It concludes that infected soil carried by vehicle movements in the area is the most likely source of transmission.
The report says: “Movements of vehicles such as those of land contractors, the Environment Agency (EA), Thames Water and other maintenance service providers could have taken fomites [an inanimate object or substance capable of carrying infectious organisms] from roads onto agricultural land.
“Depending on the type of land and environmental conditions, any virus present in fomites could have survived for some time and remained viable to infect susceptible livestock coming into contact.”
Fig. 1: The hypothetical epidemiological links between infected premises
Source: DEFRA epidemiological report