Earlier this year, vast numbers of livestock in Great Britain were affected by a foot and mouth disease (FMD) epidemic that swept through the countryside. Now, a report published in todays issue of the journal Nature examines the effectiveness of treatment strategies used to control the virus, including the slaughter of more than 3.5 million animals. "This is the most thorough analysis yet of the epidemic," says co-author Neil Ferguson of Imperial College, London. "It has enabled us to evaluate the different policies in turn and it clearly shows the need for a rapid and complete contiguous culling policy for disease control and eventual elimination."
The scientists used farm animal census data, along with disease and slaughter information, for all the farms in Great Britain to develop models of transmission rates and of the epidemic's control, which began in early February. Their findings suggest that extended culling programswhich called for killing animals on infected premises, as well as those on adjacent farms even before infection was confirmedwere essential to controlling the epidemic. Swiftness to slaughter is paramount in controlling FMD because infected animals can transmit the disease before they show symptoms and because the virus can live outside a host. The Imperial team proposes that the culling policy could have reduced the number of cases by 16 percentand saved 30 percent of the culled animalshad it been fully implemented by April 1.
The study also highlights risk factors for farms in Great Britain: large farms are more vulnerable than smaller ones; cattle farms are most at risk, followed by sheep and pig farms; and farms composed of many scattered fields have a higher risk of transmission due to increased movement of personnel and vehicles between separated land areas.
In their report, the researchers refrain from making any predictions regarding the extinction of the English epidemic. And because the virus may be more viable in colder temperatures, the scientists now urge farmers not to lift movement restrictions or relax biosecurity controls, such as the use of disinfectant on vehicles and clothing. "We will not have learnt the lesson of 1967 if restrictions are relaxed," warns co-author Christl Donnelly, referring to England's last major outbreak of FMD.