Combating FMD: A New Approach
The 2001 FMD outbreak in the United Kingdom had a major impact on control strategies, and new recommendations are emerging. Until recently, veterinarians believed that FMD-infected animals could spread the disease for several hours or days before they developed acute symptoms. For this reason, during the 2001 FMD outbreak in the UK, the British government’s strategy for containing the outbreak was to slaughter animals both on infected farms and adjacent ones, whether or not actual cases of the disease were reported. This policy, known as “contiguous culling,” led to the slaughter of more than 6 million cattle, sheep, and pigs, even though only 2 million animals were actually infected with the FMD virus.
Recent findings by a group of veterinary scientists at the Institute for Animal Health in Pirbright, England, and the University of Edinburgh may lead to a more targeted approach to the control of future FMD outbreaks. The research suggests that FMD-infected animals can transmit the disease only after they develop acute symptoms. Researchers were also able to detect FMD virus in the blood and nasal secretions of infected cattle during the time-window of about 1.7 days when an animal was infected with FMD but was not contagious to others.19 These findings suggest that contiguous culling may be unnecessary, and that future outbreaks could be brought under control by intensively monitoring herds and slaughtering animals as soon as they become ill. Removing infected animals during the 1.7-day time-window would eliminate the risk that they could infect others, thereby sharply reducing the total number of animals that have to be culled.20
The long-held belief that vaccinated animals can develop subclinical FMD infections in which they are asymptomatic but can transmit the disease to other susceptible livestock also appears to be wrong. This discovery has increased interest in fighting FMD outbreaks with “ring vaccination,” or vaccinating uninfected animals on farms surrounding the focus of an outbreak and slaughtering all infected animals within the ring. Because the asymptomatic animals are not contagious, ring vaccination should be effective at containing the spread of the disease. What is still needed, however, is a test that can clearly distinguish livestock vaccinated against FMD from those infected with the virus. This is readily possible with the next-generation recombinant vaccines.21