Explained: What is culling and how India is taking care of bird flu?

New Delhi, Jan 11: Days after culling of chickens and ducks in Kerala, the Haryana government has decided to cull poultry birds in Barwala after some of them tested positive for the avian influenza.

Bird flu, also called avian influenza, is a viral infection that can infect not only birds, but also humans and other animals. Most forms of the virus are restricted to birds. It can be seen that H5N1 is the most common form of bird flu.

What is culling?

Reduction of a wild animal population by selective slaughter of domestic poultry birds, such as chickens and ducks, to contain the spread of bird flu is called culling. During culling operations, all domestic birds in an infected area are slaughtered and their remains buried.

However, in India, culling is done in a radius one kilometre from the site of infection. This radius is called as infected zone. All domestic birds present in commercial farms, backyard farms or live bird markets in the infected zone are culled.

In India, and also in other countries, culling operations have been carried out at least since the second half of the 20th century with the advent of large commercial poultry farms where a viral disease can spread quickly.

This period also saw frequent outbreaks of the avian influenza all around the world, and the diversification of the rapidly-mutating virus into a large number of strains.

Earlier, culling took place only to stop the viral disease from spreading to birds in other farms outside the infected zone. However, it is now aimed at protecting humans, ever since the first transmission to humans in 1997.

Will the wild birds be culled?

Though wild birds may carry the bird flu, only domestic poultry birds are culled since they are present in close proximity with people, raising the chances of transmission of the virus to humans, according to the central government's bird flu action plan.

In India, culling takes place by wringing their necks. "The birds should be culled by a quick twisting of the neck (cervical dislocation), taking care that the process is humane," states the Action Plan for Prevention, Control and Containment of Avian Influenza.

In the previous bird flu outbreaks in the country, the birds were killed directly using this method, but following the recent outbreak, the plan has been revised, and now requires the cullers to first administer an oral anaesthesia to birds weighing above three kilograms.

After culling, the bird carcasses are either burnt/incinerated or buried in deep pits which are then covered with layers of lime.