Science - December 22, 2009

Migrating birds spread bird flu

The highly pathogenic avian influenza virus H5N1 has probably been spread by birds migrating from Southeast Asia to other continents five years ago. This suggestion is propounded by Herbert Prins, professor of Resource Ecology, together with researchers of the ITC in the journal Geospatial Health.

The researchers analyzed the spread of virus type H5N1 from Asia between 2003 and 2006. The spread appeared to show a seasonal pattern. The epidemic developed in three phases, in which the outbreaks took place mainly in winter and early spring. The researchers combined the outbreak chart of the virus through time with important bird migration routes in the area.
A statistical analysis shows that the virus had spread along bird migratory routes. During the first two phases of the epidemic, birds on the migratory route from East Asia to Australia were infected. In the third phase, the avian flu virus showed up along four other migratory routes: the Central-Asia flyway, the route across the Black Sea to the Mediterranean Sea, the migratory route from western Asia to eastern Africa and that in West Europe along the Atlantic Ocean. The researchers found six 'disease clusters' along these flyways and encountered disease clusters in sites where the migratory birds were known to overwinter.
There is no direct evidence yet that migratory birds have spread the avian flu virus, says Prins. 'We have carried out a statistical analysis. This makes it more plausible that migratory birds have spread the H5Ni virus. Besides the birds, animal transportation poses just as dangerous a threat in spreading bird flu.'
Prins conducted the research together with the GIS Group of the ITC in Twente and researchers from China and South Africa.