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| March
2, 2001 |
| Slaughter
Stopper |
Exclusive from New Scientist magazine
 | | A
new kind of vaccine could one day stop the mass destruction of livestock during
foot and mouth outbreaks. Photo: Corbis |
New
vaccines could one day prevent the mass slaughter of livestock during foot and
mouth outbreaks. Britain and other European countries are currently destroying
tens of thousands of animals.
Conventional vaccines exist but animals given
these 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.
And 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.
Infected or vaccinated?
The
key problem is that conventional vaccines consist of inactivated copies of the
foot and mouth disease virus. The antibodies produced against this are identical
to those produced in an animal harbouring the live virus, making it difficult
to tell one animal from the other.
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. The adenoviruses themselves
cannot 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.
Ring
vaccination
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.
Other researchers
are working on similar new vaccines, such as those at the Institute for Animal
Science and Health in Lelystad, The Netherlands, but the vaccines will not 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. | | |
