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updated 9/4/2012 4:50:42 PM ET 2012-09-04T20:50:42

Game restocking, which involves releasing millions of human-raised animals for hunters to kill, is helping to spread disease through hand-reared populations and possibly wild ones as well, according to a PLoS ONE study.

The study focused on Mallard ducks, but prior research has warned against the restocking of other animals, such as rabbits and partridges.

The life of these animals usually begins with crowded, often unsanitary conditions and ends with death by hunting.

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"Mallards are reared in high densities, share little ponds where influenza viruses can persist and their genetic diversity is very poor," lead author Marion Vittecoq told Discovery News. "These conditions favor influenza virus infections and their spread in the game bird facilities."


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Vittecoq, a researcher of health ecology at the Tour du Valat Research Center, and her colleagues conducted a two-year study in the Camargue region of Southern France to investigate the influence of hand-reared Mallard releases on avian flu virus dynamics in surrounding wildlife. The study was collaboration involving Tour du Valat, CNRS, ONCFS and the Institut Pasteur de Paris.

The scientists sampled Mallards from several game facilities before their release and identified an extremely high infection rate caused by the H10N7 strain of bird flu. Sampled ducks from the wild, before the release of the raised birds, did not have this virus. The same virus has infected humans before in Egypt and Australia.

There is some good news, however. The detected virus is a relatively low pathogenic one, and is not as virulent as strains such as HPAIV H5N1 that is currently circulating in South-East Asia and North Africa, co-author Frédéric Thomas said. So far, the virus does not appear to spread from human to human.

Vittecoq explained, "These viruses were certainly transmitted from birds to humans and (are) unable to achieve transmission from man to man."

Such a transmission would likely require a mutation of the virus, which scientists are carefully monitoring. What does not appear to be monitored well, however, are game restocking operations.

"According to French law, avian influenza surveillance should be implemented in game bird facilities, yet these measures are generally ignored," co-author Michel Gauthier-Clerc told Discovery News.

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He added, "It is important to note that this lack of sanitary control is not a French exception. As an example, this surveillance gap was also recently pointed out in the USA, while studies led in Spain warned about the epidemiological consequences of rabbit and the red-legged partridge releases."

Without dedicated testing, the viruses can be hard to detect. Some infected birds may show now visible symptoms, while others may exhibit respiratory problems and conjunctivitis.

Game restocking holds no conservation role, since "the objective of these releases is to provide lots of birds to be shot on commercial hunting estates," Gauthier-Clerc said. "They have an economic role and allow for the development of this leisure activity."

He further pointed out that hand-reared ducks, with or without the virus, have a very low survival rate if they mix into the wild population. Few of them reproduce.

The researchers do not call for the end of hunting or game restocking.

"We simply urge for the application of the law," he said. "Sanitary control should be regularly implemented in game bird facilities and released birds should be ringed. Such simple measures could permit keeping track of released birds. They could also prevent outbreaks in hand-reared Mallards and surrounding wildlife."

© 2012 Discovery Channel

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