http://www.nature.com/nsu/030106/030106-14.html

Foot and mouth strategy strengthened

Interferon could cover vaccines' weak spot.

10 January 2003

HELEN PEARSON

Vaccination was shunned by vets in 2001 as too slow to take effect.

An antiviral drug could avert future foot-and-mouth disease (FMD) epidemics, scientists say1. Combined with vaccination, the drug gives slow-acting vaccines time to kick in.

More than 6 million animals were slaughtered in 2001 as Britain struggled for 7 months to stop FMD tearing through farmyards. Vets shunned animal vaccination because the virus jumps from herd to herd before vaccines can take effect.

The antiviral drug interferon protects pigs from infection for at least 24 hours, says Marvin Grubman of Plum Island Animal Disease Center in Greenport, New York. Crucially, it starts working within a day. "No vaccine can protect animals so quickly," he says.

"It's potentially hugely significant," agrees FMD epidemiologist Mark Woolhouse of the University of Edinburgh, UK. At the time of the British outbreak, experts favoured culling over vaccination. Taking 7 days to provide immunity, a vaccine strategy might have worsened the epidemic, they feared.

Recent inquiries such as those by Britain's Royal Society have recommended well-planned emergency vaccination - alongside culling - should FMD return. "This finding tips the balance towards vaccination," says Woolhouse.

Interferon - normally a chemical cry for help from virus-infected cells to the body's immune system - is used to treat patients with hepatitis B and C. But unlike human interferon, no system exists for synthesizing large quantities of the animal protein.

To deliver the interferon, Grubman and his colleagues engineered harmless viruses to carry a pig interferon gene.

High doses of the virus delivered enough interferon to protect pigs from clinical FMD. It seems to stop the virus multiplying. And in unpublished work, Grubman's team found that a shot of interferon alongside conventional vaccination completely protected pigs from the disease for up to 5 days.

David Paton, who heads the Institute for Animal Health in Pirbright, UK, points out that the studies must be repeated in cattle - the main target for vaccination programmes.

Even so, "the work is very exciting and offers hope for the future," says Paton. The Plum Island researchers are already talking with commercial vaccine manufacturers.