MASS slaughter of millions of cattle and sheep. Vast funeral pyres trailing
smoke across the land. As the authorities raced to stamp out the raging epidemic
of foot and mouth disease (FMD) this year, the British countryside resembled
Hieronymus Bosch鈥檚 vision of hell. Every animal on every infected farm was
killed, quickly followed by those on neighbouring farms. There was, the
authorities said, no other way of stopping the disease.
Some people thought otherwise. Appalled by the medieval carnage, organic
campaigners such as the Soil Association, along with some small farmers and
vets, clamoured for a more modern response鈥攁 vaccine against foot and
mouth that government officials had in hand but refused to use. The controversy
continues to this day, with the government鈥檚 chief scientific adviser, David
King, continuing to insist the government was right not to vaccinate.
This month, vaccination policy will get another airing when scientists and
policy makers gather in Brussels for a conference on FMD convened by the
European Union in response to the British outbreak. But don鈥檛 expect them to
come up with simple answers. The benefits of vaccinating against foot and mouth
are not clear-cut. Once an outbreak starts it鈥檚 vital to halt the epidemic as
quickly as possible while minimising the number of dead animals. It鈥檚 not clear
that vaccination helps do that鈥攊t can even make the slaughter
worse鈥攁nd the prevailing opinion within agriculture is that it isn鈥檛 worth
it. Yet there is a very good argument in its favour. Vaccination can help reduce
the disease鈥檚 cost to society as a whole. For that reason alone, British
authorities were probably wrong not to vaccinate last spring.
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It鈥檚 easy to see why the idea of vaccination is so popular鈥攊t has
worked well in eradicating or limiting human diseases, such as polio, smallpox
and diphtheria. But vaccination against FMD isn鈥檛 so straightforward. To begin
with, vaccination can mean two very different practices: the routine vaccination
of all animals before any disease occurs鈥攋ust as vaccination is used in
people鈥攐r a more targeted emergency response to a disease outbreak.
The first option is easy to dismiss. FMD vaccines only protect an animal for
about six months, so routine mass vaccination is too cumbersome and expensive
unless the disease occurs so frequently that new cases are always popping up.
That is still true in some parts of the world鈥擲outh America and the Middle
East, for example鈥攁nd routine vaccination is the norm there. But in Europe
FMD is so rare that routine vaccination doesn鈥檛 make sense.
So the debate about vaccination centres on its use as an emergency response.
The idea is to contain the disease by surrounding the site of an outbreak with
vaccinated animals that are immune to the virus. One way to do this is for vets
to vaccinate all animals in the region of an outbreak as quickly as possible.
Once enough animals have been immunised, infected animals are unlikely to
encounter susceptible animals they can pass the virus on to, and the outbreak
dies out. Another, more focused option is 鈥渞ing vaccination鈥�: starting at the
edge of a circle several kilometres in radius and working inwards, vets immunise
all livestock encircling the outbreak. The British government keeps a stockpile
of FMD vaccine for emergency use, though it chose not to use it this year
because it decided the disadvantages of vaccination outweighed its benefits.
Ring-fencing an outbreak sounds straightforward, but in reality it鈥檚
difficult to pull off. The virus always has a head start of nearly a
week鈥攊nfected animals may become contagious about two days before they
develop the characteristic blisters that allow vets to recognise the disease and
start vaccinating. And then animals take four or five days after vaccination to
develop immunity. What鈥檚 more, vaccinating enough animals to complete the circle
can take several days. That gives the virus a good chance of breaking through
the cordon. 鈥淔MD moves extremely fast. You just don鈥檛 have a few days to wait
for the vaccine to take hold,鈥� says Mark Woolhouse, a veterinary epidemiologist
at the University of Edinburgh.
Still, emergency vaccination does appear to have worked in some cases. In the
Netherlands this summer, in Algeria in 1999, and in Albania and Macedonia in
1996, for example, nascent outbreaks fizzled to a halt after vaccination
programmes reached critical mass. 鈥淔ield evidence is if you get over 80 per cent
[vaccinated], then your epidemic just stops,鈥� says Keith Sumption, a veterinary
virologist at the University of Edinburgh.
But sceptics dispute whether vaccination can really take the credit for these
successes. In the heat of an FMD outbreak, no one would attempt a controlled
experiment鈥攙accinating in the north of the country, for example, and
leaving the south unvaccinated鈥攕o there鈥檚 always an alternative
explanation. The Dutch not only vaccinated, they also slaughtered a huge number
of animals. Algeria鈥檚 hot, dry climate would have killed the virus and kept it
from spreading. And perhaps the epidemic in Albania and Macedonia would have
fizzled out by itself.
Vaccine sceptics also point to two recent computer simulations that modelled
Britain鈥檚 epidemic, tracking the spread of the disease farm by farm across the
country (The Veterinary Record, vol 149, p 137; Science, vol
294, p 813). Neither found that adding vaccination to the slaughter procedure
would have made a big difference to the total number of infected farms or the
duration of the epidemic. 鈥淣one of our simulations showed it shutting down the
infection,鈥� says Matt Keeling, a zoologist at Cambridge University and lead
author of the Science study.
Discouraging as they appear at first glance, however, neither model really
settles the vaccine question because they only simulated a small number of
strategies. Keeling, for instance, simulated vaccination within a 3-kilometre
radius of infected farms, but did not test larger rings. The other simulation
modelled vaccination of cattle only, rather than both cattle and sheep.
Clearly, scientists still have much to learn about whether, and in what
circumstances, emergency vaccination can be helpful in bringing an epidemic to
heel. But one thing seems certain: vaccination can鈥檛 do the job alone. Whether
or not vaccination is part of the strategy, it鈥檚 imperative that the authorities
ban the movement of animals between farms in regions infected with the virus.
Farmers hate such movement controls, because they restrict sales and force
animals to stay on depleted pastures. But without them, the virus is almost
certain to spread out of control.
Vaccination also does not eliminate the need for large-scale slaughter,
because killing is the quickest and most reliable way to stop infected animals
from spreading the virus. So whenever the disease appears, every animal on the
infected farm and all neighbouring farms鈥攅ven if they have been
immunised鈥攎ust still be slaughtered and disposed of as rapidly and
ruthlessly as possible. There is no other effective way of stamping out the
infection once it has taken hold.
A second reason for extermination has to do with international trade. Foreign
buyers are extremely reluctant to import livestock from anywhere that has used
emergency vaccination. That鈥檚 because it鈥檚 hard to tell the difference between a
vaccinated animal and one infected with live virus. Buyers routinely test for
FMD by looking for antibodies in the animals鈥� blood, but a vaccinated animal
also carries such antibodies, so the test can鈥檛 discriminate between the
two.
Moreover, the vaccine cannot prevent immunised animals from becoming infected
with minuscule amounts of live virus in the lining of their throat, out of reach
of the antibodies in their bloodstream. There鈥檚 no good evidence such 鈥渃arrier鈥�
animals can spark an outbreak鈥攎any experts say there鈥檚 far too little
virus present to do that鈥攁nd the antibodies keep the virus from spreading
to the rest of the animal and escalating into full-blown foot and mouth disease.
But still, why should FMD-free countries take the risk?
Total shutdown
For these reasons, international regulations ban exports from countries that
have used emergency vaccination until 12 months after the last diseased animal
or the last vaccination, whichever is later. So vaccinating shuts down export
markets for a long, long time. There is a way to reduce the 12-month wait down
to 3 months鈥攕laughter all the vaccinated livestock. The Dutch followed
that route in their outbreak last spring and were able to resume exports
quickly. But the strategy has a terrible cost鈥攜ou can end up killing more
animals than if you hadn鈥檛 vaccinated.
Overall, then, a decision to vaccinate livestock in the face of an FMD
epidemic won鈥檛 avoid mass slaughter and may exacerbate it. It may not do much to
reduce the duration and size of the epidemic. And it shuts off export markets
even after the epidemic is over. Doesn鈥檛 sound very good, does it? For these
reasons鈥攅specially the last鈥攖he powerful National Farmers Union
(NFU), which largely represents big landowners and the livestock industry,
pressured the government to shun vaccination.
The government did as the NFU wished鈥攂ut in so doing, they ignored a
much larger piece of the picture. Despite its loud lobbying voice,
agriculture鈥攅specially livestock agriculture鈥攊s only a small part of
the rural economy. In Britain, for example, the countryside shut down almost
completely during the FMD epidemic, and for months afterwards rural footpaths
were closed, country dwellers encouraged not to travel, and urbanites urged not
to venture into affected areas. This curfew cost the rural economy an estimated
拢3 billion in lost tourism revenue, which dwarfs the 拢555 million a
year the meat industry earns from exports.
Vaccination would have reduced that cost by allowing rural life to return to
normal much more quickly. People or vehicles moving about the countryside are
much less likely to spread the virus to or from vaccinated farms, says Sumption,
so you don鈥檛 need to close footpaths or discourage movement within the cordon
sanitaire. 鈥淭his is where the politicians come in,鈥� says Gareth Davies, the
former chief veterinary epidemiologist for the EU, now retired. 鈥淭hey have to
balance public opinion and the losses to the tourist trade and the countryside
against the relatively small export loss.鈥� Vaccination would also have helped
farmers rescue rare breeds or valuable breeding stock from slaughter.
All the finger pointing about what should have been done this year is no
longer terribly helpful, however. The crucial question is what the authorities
should do next time FMD breaks out. And whether it鈥檚 this winter, next year or
next decade, it will happen sooner or later because of the increasing global
traffic in livestock and meat products. Right now, before the crisis, is the
time for scientists to get their story straight. So far, they haven鈥檛. Some
experts call for vaccination only when the disease threatens to spread out of
control, while others say it鈥檚 useless in such circumstances and works best
against a single, well-localised site of infection. 鈥淲e have got to work out
what the trigger points are,鈥� says Davies.
This month鈥檚 meeting in Brussels would be a good time to start doing that. If
the experts agree on one thing, it is that speed is of the utmost importance in
responding to an outbreak of FMD. Policy makers desperately need better plans in
place the next time FMD rears its head.
Instead of battling foot and mouth disease every time it flares up, why not
seize the initiative and wipe the disease off the face of the Earth? 鈥淚f I was
in charge, I would set out to free the world from foot and mouth, just like the
World Health Organization did with smallpox,鈥� says Fred Brown, an FMD expert at
the US Department of Agriculture鈥檚 Plum Island Animal Disease Center in
Greenport, New York, and former deputy director of the Institute for Animal
Health in Pirbright, Surrey. To do it, you鈥檇 need the ultimate vaccination
programme鈥攙ets would have to immunise nearly every cow, sheep, goat and
pig in the world.
It sounds like a wonderful goal, but in reality it would have only a slim
chance of succeeding. Vaccinating every herd, even in the remotest areas of
South America, Africa and Asia, would be a huge task by itself, though perhaps
just manageable. But FMD also infects deer and other wild hoofed animals, and
tracking down and vaccinating all of those would be a monumental undertaking.
Brown, however, thinks it would be possible. 鈥淚t would be a massive
thing鈥攐f course it would鈥攂ut you could set your sights on that.鈥�
However, there鈥檚 another problem. Like some vaccines used in
people鈥攏otably the cholera vaccine鈥攖he FMD vaccine does not confer
lasting immunity. That means revaccinating every 6 to 12 months, which sets a
Sisyphean task for any worldwide eradication programme. Smallpox was an easy
target by comparison鈥攙accinated people were immune for a decade or more,
and the virus only infected people.