No subject

As the foot and mouth epidemic sweeps the UK and spills into other =
European
countries, the question of whether to vaccinate or not has become =
crucial.
Here, New Scientist unravels the complexities of the arguments. 

Why is vaccination so controversial? The answer has everything to do =
with
economics and very little to do with what's good for the animals. =
Using
vaccination prevents farmers from selling animals and produce to =
countries
free of foot and mouth disease, such as the US, Australia, New =
Zealand and
Japan. Protecting these exports is also why animals with foot and =
mouth
disease, which affects productivity but is not fatal, are always
slaughtered.

But how can a vaccine jeopardize export trade? All it does is protect
animals against the virus? It's not as simple as that, I'm afraid. =
Vaccines
are not 100 per cent effective, so some animals remain vulnerable to =
the
virus. Worse still, even vaccinated animals can still carry the live =
virus.
If your country was free of disease, would you risk importing =
vaccinated
animals? 

What if vaccines were improved to be 100 per cent effective? Even =
then,
there's a problem - it's impossible to tell vaccinated and infected =
animals
apart. Current foot and mouth vaccines are made from killed virus. In =
blood
tests, these dead viruses appear the same as live ones in an infected
animal. The same is true of tests for antibodies that vaccinated =
animals
make to fight the disease - infected animals have them too. 

Isn't there any difference at all? Some researchers think there is. =
They say
that a sufficiently sensitive test could spot fragments unique to the =
live
virus (Annihilate or vaccinate, New Scientist, 31 March 2001). Also, =
new
vaccines under development make this even easier because they're =
based on
special fragments of the virus instead of killed whole versions of it =
(Why
the slaughter? New Scientist, 3 March 2001). 

Wouldn't the need to test all animals deter trade? Very possibly. =
Animals
from a country with guaranteed disease-free livestock would require no
testing, other than occasional spot surveillance. Imports from =
vaccinating
countries would require much tighter surveillance, with frequent =
screening.
Which would you choose to import? 

Any other arguments against vaccination? Indeed there are. Today's =
vaccines
don't protect the animals for very long. They wear off after about six
months so vets would have to revaccinate periodically. Also, vaccines =
seldom
protect against all seven major strains of the foot and mouth virus. 

Does anyone vaccinate? Many countries whose farmers don't depend on =
exports
to disease-free countries choose to vaccinate, e.g. China. Farmers =
who are
too poor to either vaccinate or slaughter infected animals simply =
live with
the disease, but have to accept much reduced productivity from the =
animals.
But vaccination is often used in developing countries to "ring fence"
outbreaks, preventing the virus from reaching neighbouring farms. 

But vaccination is the kiss of death for countries that want to =
export to
"disease-free" nations? Yes. It's taken as a sign that you haven't =
got the
disease totally under control. Faced with these doubts, importers =
generally
take the safe option and buy their goods from other disease-free =
sources. 

So is it totally useless in countries which strive for disease-free =
status?
No, not always. "Emergency" vaccination can be used locally to fight =
the
spread of the virus - if it can be carried out faster than slaughter.

How does emergency vaccination work? The main idea is to buy time for
overstretched slaughter teams. If livestock is condemned because of a =
nearby
outbreak, vaccinating them means that they cannot catch and spread the
disease while they await slaughter. This creates a "firewall" and =
stops the
spread of the epidemic. Another approach is "dampening down". Here, =
infected
animals are vaccinated and rapidly stop exhaling large amounts of the =
virus.
Again this slows spread and again the animals are ultimately killed.
Finally, it could in theory be used to protect rare or valuable =
breeds of
livestock, which would not be later killed but would be quarantined. 

What are the penalties if countries seeking "disease-free" status use
vaccination? Countries using only slaughter are allowed to resume =
exports
three months after the last reported case. The embargo automatically =
lasts
nine months longer if countries have used emergency vaccination and
slaughtered all the vaccinated animals. If countries allow any =
vaccinated
animals to live on, they face at least two years of purdah after the =
last
case. Britain's agriculture ministry says that this last scenario =
would cost
the country up to =A3570 million per year in lost export markets. So =
again, it
all comes down to economics. 

So how do you decide whether to vaccinate or not? You have to weigh =
up the
cost of the exports you lose if you do, against the compensation =
costs for
the extra animals you are likely to have to kill if you don't. =
Professor
David Harvey, of Newcastle University's Centre for Rural Economy, =
calculated
recently that the UK could "afford" to slaughter every 10 years and =
it would
still be cheaper than using vaccination. But not everyone agrees and =
the
picture is also complicated by the general election that the =
government is
widely believed to have planned for 3 May. 


Sam Bennett
Films Process Technician
HP Corvallis
Telnet 541-715-5142 
Pager 967-6363