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Avian Flu Update: H5 Viruses Detected Among U.S. Domestic and Wild Birds

Recent detections of highly pathogenic avian influenza H5 infections in U.S. domestic and wild birds pose a low risk to human health at this time according to the Centers for Disease Control and Prevention. In December 2014, the United States Department of Agriculture (USDA) first detected H5 avian viruses in wild birds in Washington state. Since that time, additional infections in birds with highly pathogenic avian influenza A H5N2, H5N8 viruses and with a newly identified H5N1 virus have been reported in the western states of California, Idaho, Oregon, Utah, Washington and Nevada. No human infections with these viruses have been reported to date.

Avian influenza (Bird flu) is a viral disease of birds. Migratory waterfowl and shore birds may carry avian influenza viruses that do not usually make them sick. Avian influenza viruses can be classified as either “low pathogenic” avian influenza viruses or “highly pathogenic” avian influenza viruses (HPAI), based on molecular characteristics and the ability of the virus to cause disease in birds. HPAI viruses can cause severe illness and death in birds, particularly in domestic poultry.

In general human infections with avian influenza viruses are rare and most often occur after people are in direct or close contact with an infected bird. Illnesses in humans from avian influenza virus infections have ranged in severity from mild to severe.

While no human infections with these HPAI H5N8, H5N2, or this new H5N1 virus have been reported worldwide, similar viruses (like Asian-origin H5N1, for example) have infected people in the past. The H5N1 virus recently isolated from a U.S. wild bird is a new mixed-origin virus (a reassortant) that is genetically different from the Asian-origin avian H5N1 viruses that have caused human infections with high mortality.

CDC is communicating and coordinating with state health departments on appropriate human health measures and is working with animal health colleagues to evaluate and minimize public health risk. The risk to people from these HPAI H5 infections in U.S. birds and poultry is believed to be low at this time because these viruses do not normally infect humans easily, and even if a person is infected, the viruses do not spread easily to other people. People in contact with known infected or possibly infected birds should take precautions to protect against infection. In addition, CDC has developed testing and influenza antiviral prophylaxis guidance for persons exposed to birds possibly infected with HPAI H5 viruses.

Because avian influenza A viruses have the potential to change and gain the ability to spread easily among people, monitoring for human infection and person-to-person transmission is extremely important for public health.

CDC continues to monitor this situation to minimize the risk to people and will provided updated information as it becomes available.

For more information about avian influenza visit the CDC avian flu web site and the USDA ARS and Animal and Plant Health Inspection Service (APHIS) websites.

The U.S. Department of Interior (DOI) and the USDA are the lead federal agencies for outbreak investigation and control in wild birds and the USDA APHIS is the lead agency for such activities in domestic birds. The latest information on avian influenza findings in the Pacific Flyway is available on USDA’s website.