Outbreak study: Satellite tracking reveals how wild birds may spread avian flu

US Geological Survey: For the first time, migratory birds marked with satellite transmitters were tracked during an outbreak of highly pathogenic H5N1 avian influenza virus (H5N1) in Asia, providing evidence that wild birds may be partly responsible for the spread of the virus to new areas.

In the study, scientists from the USGS Alaska Science Center and the University of Tokyo attached satellite transmitters to 92 northern pintail ducks several months before the H5N1 virus was discovered in dead and dying whooper swans at wetlands in Japan.

They found that 12 percent of marked pintails used the same wetlands as infected swans and that pintails were present at those sites on dates the virus was discovered in swans. During the first week after they become infected with H5N1, ducks such as pintails can shed the virus orally or in their feces, potentially contributing to the virus’ spread.

Researchers found that some of the marked pintails migrated 700 miles within four days of leaving the outbreak sites; marked pintails ultimately migrated more than 2,000 miles to nesting areas in eastern Russia. The study’s discovery that northern pintails made long-distance migrations during the period when an infected duck would likely shed the virus offers insight on how H5N1 could be spread by wild birds across large areas.

The research, published in the journal Ibis, does not prove the marked pintails were actually infected with the H5N1 virus or that they definitively contributed to its spread. However, it does demonstrate that pintails satisfied two requirements necessary for migratory birds to spread the virus: they used outbreak sites at times when the virus was present and some birds migrated long distances within a week of using the sites.

Jerry Hupp, Ph.D., a U. S. Geological Survey scientist and one of the lead authors of the study, noted that the H5N1 virus has been found in wild birds, including northern pintails, which show no visible signs of illness. Also, laboratory studies have shown that pintails and some other wild birds remain healthy when infected with H5N1….

Colorized transmission electron micrograph of Avian influenza A H5N1 viruses (seen in gold) grown in MDCK cells (seen in green). Avian influenza A viruses do not usually infect humans; however, several instances of human infections and outbreaks have been reported since 1997. When such infections occur, public health authorities monitor these situations closely. From the Centers for Disease Control