What is the relationship between clinical signs and transmission of foot-and-mouth disease in cattle?
Preemptive control measures for foot-and-mouth disease may be unnecessary, as animals are not infectious until after clinical signs appear, suggesting efforts should focus on early detection and rapid intervention.
Control of many infectious diseases relies on the detection of clinical cases and the isolation, removal, or treatment of cases and their contacts. The success of such "reactive" strategies is influenced by the fraction of transmission occurring before signs appear. We performed experimental studies of foot-and-mouth disease transmission in cattle and estimated this fraction at less than half the value expected from detecting virus in body fluids, the standard proxy measure of infectiousness. This is because the infectious period is shorter (mean 1.7 days) than currently realized, and animals are not infectious until, on average, 0.5 days after clinical signs appear. These results imply that controversial preemptive control measures may be unnecessary; instead, efforts should be directed at early detection of infection and rapid intervention.
Charleston et al. (Thu,) studied this question.
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