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鈥檚 a catch鈥攁nimals 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鈥檛 be able to export animals or animal products for at least this long.
鈥淭hat鈥檚 a very considerable disadvantage,鈥� Donaldson says.
And that鈥檚 not the only problem. The vaccines don鈥檛 give long-term protection
and have to be given up to twice a year. That is expensive. What鈥檚 more,
different vaccines are needed to protect against different strains of the
virus.
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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鈥檚 called 鈥渞ing vaccination鈥�, all the animals within 16
kilometres of a suspected outbreak are vaccinated.
A vaccination programme wouldn鈥檛 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鈥檚
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鈥檛 replicate.
Initial tests show that this vaccine works as well as conventional vaccines,
Grubman says. 鈥淥ne shot confers protection after seven days.鈥� 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 鈥渕arker vaccine鈥� 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.
鈥淚t should be considerably cheaper than paying farmers for the cost of
slaughter,鈥� Grubman says. And because the vaccine contains live rather than
attenuated viruses, its effect may be longer-lasting.
But such vaccines won鈥檛 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.