March 25, 2008

 

Bird flu detection in Asia not highly dependent on the number of chickens raised

 

 

Intensive rice farming and large duck populations, not the number of chickens raised, may be the best predictors of where bird flu might develop in Southeast Asia, according to researchers reviewing outbreaks in Vietnam and Thailand.

 

About 140 million birds in Southeast Asia have been killed in recent years to prevent the bird flu virus from spreading.

 

Researchers are trying to understand what factors have contributed to continued outbreaks despite significant control efforts.

 

By isolating those factors, policymakers can better target efforts to stem or prevent future outbreaks. Specifically, they could limit the movement of ducks into the rice paddies at certain times of the year, which would reduce the prospects of the virus being exchanged between domestic ducks and wild birds.

 

Researchers reviewed three outbreaks in early 2004 through late 2005. They looked at five variables, namely duck abundance, human population, chicken numbers, elevation and rice cropping intensity.

 

The research concluded that monitoring duck populations for bird flu and tracking rice paddies by satellite were the best ways to predict where outbreaks were most likely to occur.

 

The group of researchers said that chickens are no longer a highly significant predictor of the presence of the bird flu virus for Vietnam and Thailand.

 

Marius Gilbert of the Free University of Brussels, Belgium said that essentially, the virus is so pathogenic in chickens that it kills them before they can spread it.

 

The outbreaks were most concentrated in regions where rice is cultivated two or three times a year.

 

The studies note that rice paddy fields are an important habitat of free-ranging ducks, but also for wild waterfowl exploiting the same food resource in the wintering season. Thus, they may form a critical risk factor in virus introduction, persistence and spread.

 

The researchers described the predictive power of their models as moderate. They also said that their work appeared to warrant development of maps in other Southeast Asian countries identifying those areas most susceptible to future bird flu outbreaks.

 

Since 2003, bird flu has killed at least 236 people. Although it has been hard for people to catch, experts worry the virus could mutate into a form that passes easily among humans, sparking a pandemic. So far, most human cases have been linked to contact with infected birds.