why In wild birds, epidemics spread through water

The H1N1 virus currently threatening the planet with pandemic influenza A. But what about his notorious cousin, H5N1 and other avian influenza viruses? Researchers at the Institute of Development Research has studied bird populations in the Camargue and discovered that the virus could persist in the water.

Vol de flamands roses en Camargue dans le sud de la France, le 22 avril 2009.

Theft of flamingos in the Camargue in southern France, April 22, 2009.
(c) AFP
Les virus bird flu not present little risk of contamination for humans. Indeed, it is not transmissible from human to human. These do not contract the disease through close contact, prolonged and repeated with infected animals.

However, while H1N1 is not highly virulent, some viruses such as H5N1, can cause severe disease, whose outcome can be fatal. In birds, the situation is more complex: the symptoms are variable, a benign disease in wild birds to a rapidly fatal infection in domestic poultry.

How an epidemic says it? Until now, developing countries were stigmatized, including H5N1, accused of contaminating the North via migratory birds. An explanation a bit faster by IRD researchers who show that outbreaks and migration are not synchronous.

To understand how outbreaks occur, the researchers compiled data on demographic and epidemiological circulating in wild birds in the Camargue from September 2005 to July 2006. For some 250 bird species, the Camargue is a vital staging area in autumn and early spring on their journey between Europe and Africa. A position that makes this wetland in south-eastern France a “hot spot” potential for the introduction and transmission of pathogens from wild birds.

Ducks, sparrows, gulls, herons and flamingos, … over 90 species have been reviewed. The scientists then developed a mathematical model that reproduces the dynamics of virus and host populations – the birds. Result? Migration and outbreaks of influenza did not coincide. The former do not fully explain the dynamics of disease observed.

Epidemics are not necessarily due to the arrival of birds. The virus particles are persistent in the aquatic environment and outbreaks are triggered by one or more other factors. The work by researchers from the IRD shall be published in the newspaper Infection, Genetics and Evolution.