Bird flu vaccination could lead to new strains (NEW SCIENTIST)

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Note the 5 Feb 2004 link below; could it be that " NEW SCIENTIST " (one of top

real science publications) is deserting party line?

Take care, " Shaaag "

 

Bird flu vaccination could lead to new strains

19:00 24 March 2004

Exclusive from New Scientist Print Edition

Debora MacKenzie

 

 

 

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Avian influenza, WHO

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Vaccinating chickens may be the only way out of the bird flu nightmare in

Asia. But it could also lead to the evolution of new strains, the latest

research shows, increasing the risk of a human pandemic.

Only intensive surveillance can stop this happening, but experts say the

countries affected do not have the necessary systems in place.

Last week China declared its bird flu outbreaks had ended. Health officials

are vaccinating millions of the birds that escaped slaughter. Indonesia is also

vaccinating, and other Asian countries hit by the H5N1 bird flu are considering

the same strategy.

But the H5N1 virus is almost certainly still circulating among the vaccinated

birds, and the fear is that in this abnormal setting it may evolve into a form

that is not only fatal to people, like the current one, but can also spread from

person to person.

Research in Mexico has shown for the first time that under these conditions

bird flu evolves at an unprecedented rate, with unpredictable consequences.

Silent epidemics Veterinary scientists usually prefer to control livestock

epidemics by destroying sick and exposed animals, instead of vaccinating.

The reason is that vaccines, especially flu ones, are not 100 per cent

effective. While they prevent animals falling ill, low numbers of viruses can

still replicate inside their bodies and spread from animal to animal. Such

" silent epidemics " are very hard to spot, but can cause new outbreaks if

unvaccinated animals are exposed or if vaccination ends.

But with H5N1 bird flu now affecting a huge area of Asia, vaccination could

help end the outbreaks more quickly. Fewer flocks destroyed would leave fewer

small-scale poultry farmers destitute. " They really have few choices now, " says

Ilaria Capua of the World Organisation for Animal Health reference lab for bird

flu in Legnaro in Italy.

There is a precedent & shy; but it is a worrying one. In 1995 Mexico stopped an

outbreak of severe H5N2 flu by vaccinating chickens. But the virus is still

circulating silently, and Mexico is still vaccinating.

Normally the bird flu virus changes little in chickens, because it rarely

persists long enough, says David Suarez of the US Department of Agriculture's

poultry research lab in Georgia. But in Mexico the virus has been exposed to

vaccinated chickens for years and this has encouraged new forms to evolve.

Major differences In a report that will appear in the Journal of Virology,

Suarez's team reveals that " major antigenic differences " have been found in the

bird flu viruses isolated from vaccinated chickens in Mexico since 1995. It is

increasingly different to the vaccine strain, which means that infected birds

will shed more of the virus and spread the infection more readily.

The H5N1 virus circulating in vaccinated chickens in Asia is likely to evolve

the same way. There has already been speculation that vaccination programmes in

China may have led to greater genetic diversity in the virus over the past two

years, and perhaps even contributed to the emergence of the current strain ( New

Scientist, 28 January).

It is possible, however, to eradicate wild virus like H5N1 from vaccinated

flocks. The key is to detect and destroy silent infections. The low-tech way of

doing this is to place unvaccinated birds next to vaccinated flocks.

If any flu is circulating, these " sentinel " birds will develop obvious

symptoms. The weakness of this system, says Capua, is that farmers who want to

save their flocks from destruction can cheat by replacing any sick birds.

Marker vaccine The high-tech method is to use a marker vaccine that elicits

the production of a different set of antibodies to the wild virus. Antibody

tests can then distinguish between infected birds and those that have simply

been vaccinated. In 2002 Italy became the first country to eradicate bird flu

using a marker vaccine and regular testing.

The surveillance part is vital, Capua says. " The vaccine used without this

monitoring can have a boomerang effect, and become a tool to spread the virus,

not control it. "

Richard Webby, a leading flu expert at St Jude Children's Research Hospital in

Memphis, Tennessee, agrees. " The key to using vaccination successfully is strong

surveillance, with a vaccination versus infection marker, " he says.

China does at least have the right vaccines. Its agriculture ministry

announced last week that it is launching two marker vaccines. But thousands of

vaccinated chickens must still be tested, and infected flocks destroyed, to

eliminate the virus.

Yet such surveillance systems will be a tall order for the Asian countries

that are vaccinating or plan to. Joseph Domenech, head of animal health at the

UN Food and Agriculture Organization, says that Indonesia, which is vaccinating

chickens, does not have adequate controls. " In China, we just do not know, " he

says, while Vietnam has not revealed its plans.

 

 

 

 

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