Domestic ducks may be a silent reservoir for H5N1 avian influenza virus and be playing a greater role in the spread of the disease than previously thought, three international health organizations reported today. A laboratory sudy of domestic ducks infected with several strains of H5N1 virus isolated in 2004, compared with infections caused by viruses from 2003, showed that domestic ducks were shedding the virus for longer periods and without showing signs of illness, the Food and Animal Organization of the United Nations, the World Health Organization and the World Organization for Animal Health (OIE) reported in a joint statement. The study found the quantities of virus shed by healthy-looking ducks appoached thoses shed by visibly diseased chickens. The finding follows previous evidence that the virus has become more virulent in chickens and mice and is now infecting mammals, notably domestic cats and tigers, that had not been previously considered susceptible, the organizations reported. The agencies called for research to determine how widespread avian flu is in ducks and to determine the effectiveness of existing vaccines on duck populations. The agencies also said health officials in affected countries, primarily Asia, should consider exposure to ducks as a possible route of infection. <HOME>
