Researchers at the Institute for Animal Health (IAH), Pirbright, are close to a breakthrough which could stop outbreaks of foot-and-mouth disease (FMD) turning into unnecessary and costly slaughter.
FMD is the most damaging of all animal diseases. The 2001 UK outbreak infected 2000 farms and saw the slaughter of 6.5m animals at a cost to the UK economy of £8.5bn. While the 2007 outbreak affected fewer farms directly, it significantly hindered trade on thousands of livestock units.
Government policy in 2001 was to slaughter cattle within 24 hours of a vet diagnosis based on symptoms. Samples sent to the IAH’s Pirbright Lab, Surrey, for confirmation took an average of a day to arrive, which meant animals were usually dead before their tests came back.
But FMD was not found at about 23% of premises classified as infected and where a cull was implemented. "What was learned from 2001 is there is an urgent need for a fast and reliable diagnostic technique which could be used on farms by non-specialists," says Juliet Dukes, a molecular biologist and senior research scientist at Pirbright.
IAH aims to fill the gap by developing field tests that could support clinical diagnosis without waiting for laboratory results.
Field testing has many challenges. FMD is a virus which mutates rapidly. Devices need to be sensitive enough to detect tiny traces of the virus during the earliest stages of infection, or risk the dramatic consequences of a false negative result.
Equipment also needs to be cheap enough to be disposed of after each test, otherwise time-consuming sterilisation is required between farm visits.
A number of methods are at the prototype stage. One detects the protein coat of the virus using a lateral flow device similar to a home pregnancy test. A coloured band can form rapidly when the virus is present in reasonable quantity. This technology is robust and cheap to manufacture, but not sensitive enough to confirm unequivocally that FMD virus is not present.
Dr. Dukes is now part of a team developing a technique called Loop Mediated Isothermal Amplification (LAMP) for FMD detection in the field.
A saliva, blood or tissue sample is dropped into the LAMP solution, which exploits the activity of Bst polymerase, an enzyme originally used for gene sequencing. It generates so much DNA during the reaction that the result can be seen by the naked eye within 30 minutes.
The proposed device includes a small vial of orange fluid. "When it turns green during the test we have a confirmed FMD diagnosis," she explains.
Source: Farmers Weekly Interactive, January 4, 2008 by Jonathon Rees