Scientists studying foot-and-mouth disease have found that cattle with the virus are infectious for only a very short time — suggesting that mass culling previously used to reduce the disease’s spread may in future be avoided.
In research published in the journal Science on Thursday, scientists found that even if the foot-and-mouth disease (FMD) virus is detected in a cow’s blood sample, it does not necessarily mean the cow is infectious at that time.
In fact a cow with FMD is only infectious for around 1.7 days, they said.
Mark Woolhouse of Edinburgh University, who worked on the study, said the finding significantly altered scientists’ thinking about FMD and may have implications for other diseases too.
“This study shows that what we thought we knew about foot-and-mouth disease is not entirely true,” he said. “So what we think we know about human influenza and other infectious pathogens might not be completely accurate either.”
Foot-and-mouth disease is one of the world’s most important infectious diseases of farmed animals and it is regarded as a major economic threat in Europe.
Countries where FMD is endemic — in parts of Asia, Africa, the Middle East and South America — can spend vast amounts of money vaccinating their cattle every few months and farmers are often forced to kill off large numbers of livestock if a case of FMD is confirmed among their herds.
In 2001, Britain suffered one of the largest FMD epidemics to hit a developed country in several decades and millions of animals were culled and their corpses burned on huge pyres. The outbreak devastated the nation’s farming industry and cost Britain an estimated 8.5 billion pounds (US$14 billion).
Woolhouse worked with Bryan Charleston and colleagues from Britain’s Pirbright Laboratory on new kinds of experiments in which they infected “source” cows with the FMD virus and then studied how it was transmitted to other, uninfected cows.
“We have pinned down, very specifically, the relationship between when the animals are infectious… and when they show clinical signs of the infection,” he explained at a briefing about the study.
The researchers found that diagnosis of FMD infection is possible during the approximately 24 hours before the animal becomes infectious.
This suggests farmers might have time to remove the infected animals from a herd before they transmit the virus to others, potentially saving many animals from being culled.
Charleston described the discovery as good news but cautioned that it would be some years yet before the findings in laboratory conditions could be translated into new disease control methods capable of handling a real large-scale outbreak.
“This result emphasizes the need for practical tools for pre-clinical diagnosis and at present we don’t have an affordable, reliable test to use on farms,” he said.
“We can identify infected cattle before they show signs of disease using tests in the laboratory. The next challenge is to do it in the field during an outbreak.”