The foot-and-mouth outbreak in the UK remains out of control, according to two leading UK specialists in animal diseases. Clearing it from Britain's farms represents a "formidable challenge".
Controlling such a disease is a particular difficulty given the active international trade in livestock, according to Prof Mark Woolhouse of the University of Edinburgh, who advises the UK government, and Dr Alex Donaldson, head of the Pirbright Laboratory of Britain's Institute for Animal Health.
The two collaborated on a discussion of the science of controlling disease outbreaks in a report today in the journal Nature. They suggest a lack of information about livestock populations is hampering efforts to stamp out the disease.
"A flourishing international livestock trade means that we are not just living in a `global village', we are living on a global farm," they write. "One solution to this may be to impose minimum periods of residency before livestock which have moved between holdings can be moved again." (The UK government has signalled its intention to move in this direction).
The Irish Department of Agriculture's active pre-emptive slaughtering policy is suggested as a way to curb the disease. The key, they argue, is to reduce the time between the reporting of disease and the slaughter of animals at risk. "If pre-emptive culling of `at risk' animals is delayed by even a few days, those animals might transmit the infection to other holdings."
They cite recent studies of foot-and-mouth epidemics which showed that reducing the period between detection and slaughtering could help reduce the size of an epidemic. The interval between detection and slaughter during a 1982 "incident" in Denmark averaged just 15 hours and the epidemic was contained after 22 outbreaks. This interval has been between two and three days during the current UK epidemic, they say. "It is likely that delayed slaughter times have had a significant impact on the epidemic's scale," they write.
The epidemic is considered to be "out of control" given that each detected outbreak generates on average more than one subsequent outbreak. This ratio must be reduced to less than one on average before the epidemic could be viewed as contained and in decline. Even after this is achieved there is likely to be prolonged tailing-off of outbreaks, the scientists believe. A research priority must be the development of a cheap, rapid diagnostic test that can detect the presence of the virus before clinical signs of disease become apparent.
Good-quality "demographic information" on the size and population density of UK herds is also necessary. This would help establish "whether changes in the demography of livestock as a result of intensification of farming have contributed to the severity of the current FMD epidemic" and if this predisposes Britain to future disease outbreaks.
