Airborne risk is reassessed
Airborne risk is reassessed
WHEN foot-and-mouth is diagnosed and movement restrictions fully implemented, airborne spread to neighbouring farms will only occur when pigs or large numbers of cattle/sheep are infected, according to recent research.
There is virtually no risk of pigs contracting F&M from neighbouring units unless they have direct contact with infected animals, says Institute of Animal Health director Chris Bostock.
"Similarly, the risk of spread between sheep on different farms is low because they need to be within 100m of an infected flock containing 100 virus excreting animals."
However, in the current outbreak, blood data suggests the disease progressed slowly within sheep flocks and it is unlikely that this number of animals were secreting virus at the same time.
"The greatest risk of airborne spread is for cattle downwind of an infected pig unit. A herd of cattle within 6km of an infected pig unit, containing 1000 infected animals, is at risk of becoming infected. However, when the pig unit contains 100 infected pigs, the distance for airborne spread is reduced to 2km," says Prof Bostock.
"This shows consideration of what species are infected and what species are at risk is needed before action is taken on contiguous farms. For sheep, culling is justified as they may have been exposed to sufficient airborne virus and only be showing mild symptoms."
With cattle, intensive surveillance is an alternative option to culling as the disease is easily detected and animals can be removed before producing large amounts of airborne virus. *