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Update: Outbreaks of Avian Influenza A H5 in U.S. Wild and Domestic Birds: Human Health Implications

March 20, 2015 -- Ongoing outbreaks of highly pathogenic avian influenza (HPAI) H5 viruses in U.S. domestic and wild birds have the potential to cause human infections, according to the Centers for Disease Control and Prevention (CDC). While no human infections with these particular viruses have been reported at this time and CDC believes the risk of human infection is low, similar H5 viruses have infected people in other parts of the world and it’s possible that human infections associated with these viruses may occur in the United States. Most human infections with similar HPAI viruses in other countries have occurred after prolonged and close contact with infected birds. CDC has issued public health guidance for HPAI H5 testing and preventive medication of people exposed to these viruses and recommends general precautions for the public.

In December 2014, the United States Department of Agriculture (USDA) first detected HPAI H5 avian viruses in wild birds in Washington state. Additional infections with HPAI H5N2, H5N8 and a newly identified reassortant H5N1 virus were reported in domestic and wild birds in western states in the so-called Pacific flyway. There are four U.S. migratory bird pathways in the United States [327 KB, 6 pages]: the Pacific, Central, Mississippi and Atlantic. In March 2015, USDA confirmed HPAI H5 viruses in commercial turkey flocks in the “Mississippi” flyway (Minnesota, Missouri and Arkansas) and in a backyard flock in the “Central” flyway (Kansas).

Avian influenza (bird flu) is a viral disease of birds. Migratory waterfowl and shore birds are the animal hosts of these viruses and can carry avian influenza viruses without showing any signs of disease. Avian influenza viruses are further classified as either “low pathogenic” or “highly pathogenic” based on molecular virus characteristics and the severity of disease they cause in chickens in a laboratory setting. HPAI viruses may cause severe illness and death in poultry. While rare, human infections with both LPAI and HPAI viruses have occurred with symptoms ranging from mild (for example, conjunctivitis or mild influenza-like-illness) to severe (for example, pneumonia, multi-organ failure and even death).

CDC Risk Assessment

Most human infections with avian influenza viruses (including Asian HPAI H5 viruses and LPAI H7N9 in China) have occurred in people with direct or close contact with infected birds. Limited transmission from person-to-person has been documented rarely, after very close and prolonged contact with someone who is sick. Sustained human-to-human transmission with avian influenza has not been documented.

CDC considers the risk to people from these HPAI H5 infections in U.S. birds and poultry to be low at this time because infections with avian influenza viruses are rare and – when they occur – these viruses have not spread easily to other people. However it’s possible that human infections with HPAI viruses associated with these outbreaks in birds may occur at some time.

The U.S. Department of Interior and the USDA are the lead federal departments for outbreak investigation and control in wild birds and the USDA’s Animal and Plant Health Inspection Service (APHIS) is the lead agency for such activities in domestic birds. 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.

CDC Recommendations

As a general precaution people should avoid wild birds and potentially infected domestic poultry; observe wild birds only from a distance; avoid contact with domestic birds (poultry) that appear ill or have died; and avoid contact with surfaces that appear to be contaminated with feces from wild or domestic birds.

CDC recommends that people who have had contact with infected bird(s) monitor their own health for possible symptoms. People who have had contact with infected birds may also be given influenza antiviral drugs preventatively. The domestic HPAI H5 viruses that have been tested at CDC are susceptible to the recommended antiviral drugs oseltamivir, zanamivir and peramivir. While antiviral drugs are most often used to treat flu, they also can be used to prevent infection in someone who has been exposed to influenza viruses. When used to prevent seasonal influenza, antiviral drugs are 70% to 90% effective. Health care providers evaluating patients with possible HPAI H5 infection should notify their local or state health departments which in turn should notify CDC. The agency is providing case-by-case guidance at this time.

There is no evidence that any human cases of avian influenza have ever been acquired by eating properly cooked poultry products. The U.S. poultry industry maintains rigorous health and safety standards, including routine monitoring for avian influenza. It is safe to eat properly handled and cooked poultry. (For guidance on handling and cooking poultry and game birds, please visit the USDA Food Safety and Inspection Service website.)

Because of the possibility that avian influenza A viruses could change and gain the ability to spread among people, monitoring for human infection and person-to-person transmission is extremely important for public health. The U.S. Government supports international surveillance for influenza viruses with pandemic potential. CDC is following the domestic HPAI H5 situation closely and coordinating with partners.

Routine Preparedness Measures

CDC takes routine preparedness actions whenever a new virus with pandemic potential is identified. CDC has received two domestic HPAI H5 virus samples (e.g., H5N8 and H5N2) and is studying these viruses. In addition to antiviral susceptibility, the agency is conducting genetic analysis to look for genetic markers that might be associated with greater disease severity, transmissibility or other characteristics. Studies in mice and ferrets also are being conducted to evaluate transmissibility and disease severity of these viruses in animal models. In addition, the agency will study whether existing H5N1 vaccines in the Strategic National Stockpile might protect against any of the HPAI H5 viruses that have been detected in the United States as well as creating candidate vaccine viruses that are specific to the new domestic H5 viruses which could be used to make vaccine if one were needed. Information from these studies will further inform the agency’s risk assessment.

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Background on Recently Detected HPAI H5N8, H5N2 and H5N1 Viruses

The HPAI H5N8 viruses detected in the United States are similar to viruses that were first reported on duck farms in China in 2009-2010. During 2014, similar HPAI H5N8 viruses were found in wild birds and poultry in Korea and Japan. In November 2014, HPAI H5N8 in poultry and wild birds was reported in England, the Netherlands, Germany and Italy. No human cases have been associated with these HPAI H5N8 viruses.

The HPAI H5N2 viruses detected in the United States are similar to HPAI H5N2 viruses first detected in early December 2014 on poultry farms in British Columbia province, Canada. This is a reassortant virus that combines genes from Eurasian H5 viruses and North American N2 viruses. No human cases have been associated with either the North American or the Eurasian lineages of HPAI H5N2 viruses.

The HPAI H5N1 virus detected in the United States is a reassortant virus with genes from HPAI H5 Asian viruses and low pathogenic North American viruses.

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.