New Scientist
Vaccines
against foot and mouth disease exist, yet mass slaughter of livestock remains
the only way Britain can stamp out its worst outbreak for decades, say experts.
So far, almost 350 pigs and 40 cattle have been destroyed at the farms
where outbreaks have so far been identified. At least 200 more cattle were due
to be destroyed on Friday.
Foot and mouth disease is caused by a highly
infectious virus which animals either eat or inhale. It affects all cloven-hoofed
animals, which develop painful blisters around the mouth and feet.
The
animals lose their appetites and become lame. When the blisters burst, they release
virus particles that infect healthy animals. As few as 10 virus particles can
cause the disease in cows.
Reservoir hogs
Vaccination of
animals may appear to be the best way to protect against the disease, but it seldom
works in all animals. And even successfully vaccinated animals can still harbour
the foot and mouth virus for up to two years, posing a continuing risk to unvaccinated
animals.
"Cattle become persistently infectious," says Paul Kitching, head
of the world reference laboratory which tracks global foot and mouth outbreaks
from the UK Institute for Animal Health's facility in Pirbright, Surrey.
"The
upshot is that you'd have to keep vaccinated and unvaccinated animals apart,"
he says. "If the epidemic became really large, we might use vaccination to dampen
things down, but in the current UK case, it's not the first course of action."
Money matters
However, the key factor weighing against vaccination
is economic. Because they still harbour the live virus, exports of vaccinated
animals or produce from them could still spread the disease to livestock in other
countries.
An embargo imposed by the European Union on potentially infectious
produce from Britain could be lifted as early as 1 March if the disease can be
brought under control through slaughtering. "The embargo would last much longer
if you had vaccinated animals," says Kitching.
Ironically, routine vaccination
against foot and mouth disease is seen by potential customers in other countries
as a sign that the virus is still at large. So instead of providing reassurance,
it raises doubts in customers' minds.
In some poorer countries where farmers
simply rear livestock for themselves or for local trade, vaccinations are more
common. But Yves Cheneau, chief of the UN FAO's Animal Health Service says: "Vaccination
is very costly and has to be repeated annually."
It can cost up to a dollar
per dose, he says, and those countries that can not afford to slaughter or to
vaccinate just learn to live with the virus.
Dominant strain
Kitching
says that the "Pan-Asian topotype" strain infecting the British herds is extremely
infectious, and is becoming the dominant strain worldwide since emerging in India
in 1990.
Last year, it caused outbreaks in Japan, Korea and South Africa,
countries where the strain had never been seen before. Japan and South Africa
"slaughtered it out", says Kitching, whereas Korea turned to vaccination.
In
Britain's last major outbreak in 1967, 442,000 animals were slaughtered at more
than 2000 farms. The outbreak cost farmers £150 million. |
