Chickens that died from the H5N1 avian influenza in Russia may have caught the disease from migratory birds that traveled from China, hundreds or thousands of miles away, scientists said.
An analysis of viruses isolated from the poultry shows a similarity to those taken from wild geese and ducks known to have caught the disease in a Chinese lake region, researchers led by Aleksandr Lipatov of the US Department of Agriculture said today in a study. More than 1 million Russian chickens and other poultry died of bird flu or were culled to stop the outbreak, which occurred in 2005 and 2006, the researchers said in the April issue of Emerging Infectious Diseases. While more research is needed to prove a link, the study suggests that wild birds may have been the cause. The results „indicate a correlation but do not prove conclusively that wild migrating birds are the primary source of influenza (H5N1) infection of poultry in Russia,” the researchers said in the journal, published by the US Centers for Disease Control and Prevention, based in Atlanta.
While still contagious only in birds, H5N1 is deadly to humans. Scientists are monitoring the virus, which has infected 278 people and killed 168 of them since late 2003, to see if the infection begins spreading quickly in humans. The role of migratory birds in spreading H5N1 is poorly understood, according to the World Health Organization in Geneva. Researchers have debated how much, if any, of the spread of H5N1 from Asia to Africa, the Middle East and Europe has occurred through migratory birds. The virus is more likely to reach new areas through the sale and shipment of poultry.
The virus hasn't been seen in North America. Robert Webster, a virologist at St. Jude Children's Research Hospital in Memphis, Tennessee, has said that smuggled birds or poultry are more likely to bring the virus to that continent than are migratory birds. The US Agriculture Department released a report this week saying that sick birds with H5N1 probably wouldn't be strong enough to migrate to Alaska from Asia. Lipatov and Russian government scientists studied seven flu viruses taken from poultry in western Siberia and other parts of Russia during the outbreak.
There was a close genetic between the viruses and others from the Qinghai Lake region of China, where migratory birds were found infected in 2005. The viruses also showed signs of having undergone reassortment, a genetic process that can help them adapt to new organisms or conditions, the researchers said. „Until other possible routes of viral dissemination are analyzed and excluded, whether wild migratory birds are the primary source of influenza (H5N1) virus transmission and infection of poultry cannot be conclusively determined,” the researchers concluded. (Bloomberg)