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TO TACKLE the foot and mouth outbreak, Britain is destroying thousands of
animals. For now, mass slaughter remains the only option for countries 
that
want to resume exports as soon as possible. But new vaccines could one day
provide another way.

Some people are asking if mass slaughter is justified when there are 
already
vaccines against the disease. But there's a catch-animals given 
conventional
vaccines can harbour the live virus for up to two years and pass it on to
unvaccinated animals, says Alex Donaldson, head of the Institute for 
Animal
Health in Pirbright, Surrey. If Britain resorted to vaccination, it 
wouldn't
be able to export animals or animal products for at least this long. 
"That's
a very considerable disadvantage," Donaldson says.

And that's not the only problem. The vaccines don't give long-term
protection and have to be given up to twice a year. That is expensive.
What's more, different vaccines are needed to protect against different
strains of the virus.

Vaccination is common in countries where farmers rear livestock for
themselves or for local trade. Other countries use vaccination only to
control outbreaks. In what's called "ring vaccination", all the animals
within 16 kilometres of a suspected outbreak are vaccinated.

A vaccination programme wouldn't help Britain start exporting animals 
again
because conventional vaccines consist of inactivated viruses. This makes 
it
difficult to tell a vaccinated animal from one harbouring live virus.

But Marvin Grubman and his colleagues at the US Department of 
Agriculture's
secure research facility on Plum Island, New York, are developing a 
vaccine
that will make the job easier. They have inserted the genes that code for
the foot and mouth viral coat into live human adenoviruses. When animals 
get
this injection, infected cells produce the foot and mouth viral coat and
trigger an immune response. But the adenoviruses themselves can't 
replicate.

Initial tests show that this vaccine works as well as conventional 
vaccines,
Grubman says. "One shot confers protection after seven days." Crucially, 
the
adenovirus contains the genes for only a few of the foot and mouth viral
proteins. So testing blood for antibodies to the missing viral proteins 
can
easily distinguish between vaccinated and infected animals.

Grubman says that such a "marker vaccine" could be used to ring vaccinate
animals in countries such as the US and Britain in the event of an 
outbreak.
You could then test vaccinated animals regularly to see if they have been
exposed to the wild virus. If none is found, the country could be declared
disease-free.

"It should be considerably cheaper than paying farmers for the cost of
slaughter," Grubman says. And because the vaccine contains live rather 
than
attenuated viruses, its effect may be longer-lasting.

But such vaccines won't reach the market soon. And even when they do, the
disease could still spread during the seven-day delay before protection
kicks in. For the moment, it looks as if the slaughter will continue.

Michael Le Page