9 November 2001

Vaccinated or infected? New F&M test will make its mark

By Marianne Curtis

THE lack of a test to differentiate between vaccinated and infected animals in this years foot-and-mouth outbreak was a key block to use of vaccination. But this could change in any future outbreak following development of an F&M marker test by animal health company Intervet.

Part of the NFUs decision to take an anti-vaccination stance during the epidemic was influenced by the lack of a test to distinguish between vaccinated and carrier animals. In a document explaining its position, it said this would seriously complicate the lifting of F&M-imposed trade restrictions.

But large numbers of blood samples taken during the F&M outbreak have allowed refinement of an F&M marker test known as 3ABC, which is now ready for registration, according to Intervet head of vet services James Allcock.

"A European review of a research programme conducted between 1994 and 1997 concluded that the technology to differentiate between an animal infected with F&M and vaccinated against it existed. But the field trials phase was missing.

"The current outbreak provided the opportunity to evaluate how the test worked using vast numbers of blood tests from the field."

Following trials, Mr Allcock is confident the test will work with more than 99% accuracy on any strain of F&M virus. The tests success hinges on its ability to detect differences between antibodies produced against F&M virus in infected animals and those produced in response to vaccination.

In naturally occurring F&M virus, proteins known as non-structural proteins (NSPs) are associated with virus particles, says Mr Allcock. "As well as producing antibodies against the virus itself, animals also produce antibodies against NSPs. But when modern F&M vaccines are produced, NSPs are removed in the purification process, so the animal only produces antibodies against the virus."

The F&M marker test checks for presence of NSP antibodies, which are detectable in infected animals, but absent in vaccinated animals.

Had vaccination and the test been approved for use in the current F&M outbreak, it could have helped control disease spread, believes Mr Allcock. "Vaccination decreases the chance of animals becoming infected with F&M and makes them less capable of infecting other animals, slowing F&M virus spread.

"It would also help with manpower managment during F&M outbreaks. Not being able to cull animals within 24 hours is less of a problem when they have been vaccinated."

Although British Cattle Vet Association president Dick Sibley says the test has possibilities, he has reservations. "Animals vaccinated while they are incubating F&M could still shed virus. This test determines whether they are carrying antibodies to F&M virus – which can take up to 14 days to develop – not virus itself.

"This means they could still pose an infection risk to other animals. Ideally, we need a test which can quickly tell us whether an animal is carrying virus." &#42

F&MMARKERTEST

&#8226 Identifies vaccinated animals.

&#8226 Refined during current outbreak.

&#8226 On point of registration.