Is culling only solution for preventing bird flu?
Even as several thousands of chickens are being culled to prevent an outbreak of bird flu, an international report says that culling alone may not stop the spread of H5N1 virus.india Updated: Mar 19, 2006 13:42 IST
Even as several thousands of chickens are being culled to prevent an outbreak of bird flu, an international report says that culling alone may not stop the spread of H5N1 virus.
Instead of culling, the most susceptible birds in the infected areas should be vaccinated before the disease hits. This is particularly useful in the crowded poultry farms. Only this will stop an outbreak from spiralling out of control, says a report published in the March 2006 edition of New Scientist.
When such outbreaks occur, the standard response is to slaughter the infected birds and all other poultry within a certain radius. The tactic appears to have worked in Eastern France where 11000 turkeys at the infected farm were slaughtered, but this part of France was lucky in having relatively few poultry farms.
In high density areas it could be a different story, says Arjan Stegeman of Utrecht University in the Netherlands. When Stegeman and his team analysed what happened during the 2003 Dutch outbreak, they found that such measures were barely able to contain the virus in the areas of high poultry density. The country’s poultry industry was hit hard as a result and is only just recovering now.
“If H5N1 takes hold, an entire livestock industry could face ruin. It woun’t just be the farmers who would have to pay the price,” says the report.
This comes in the backdrop of the European Union’s refusal to use pre-emptive vaccination. The authorities object that this would allow the virus to circulate undetected in the vaccinated animals and they would show no obvious symptoms. The virus circulating in vaccinated chickens can mutate into potentially more dangerous forms. This had happened to H5N2 bird flu in Mexico and may have encouraged the emergence of the lethal ‘ Z genotype’ of H5N1 in China.
The vaccinated chickens should be regularly tested and culled if tested positive. Key to this is the use of a marker vaccine that triggers the production of a slightly different set of antibodies to those induced by the wild virus. Antibody tests can then distinguish between the infected birds and those that have simply been vaccinated.
The scientists cite the experience of intensive poultry rearing region near Verona in northern Italy, which after suffering repeated outbreaks of bird flu has been vaccinating high-risk flocks against H5 and H7 bird flu for more than a year.
The outbreaks have stopped and Italy now exports meat. Animals are routinely tested for signs of infection and are safe to eat.
The birds most in need for vaccination are Turkeys which are particularly sensitive to the virus. Broiler chickens raised indoors have far less contact with the outside world and may not need vaccination.