In a follow-up on the recent bird flu infections in wild and domestic birds in the United States (HERE and HERE), the Centers for Disease Control and Prevention (CDC) released the following statement:
The U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspective Service (APHIS) announced the first detection of highly pathogenic avian influenza (HPAI) viruses in a U.S. commercial poultry flock. This follows detections of HPAI A(H5) viruses in wild birds in the United States in the preceding weeks. The detection of these viruses in poultry does not change the risk to the general public’s health, which CDC considers to be low. However, outbreaks in domestic poultry, in addition to infections in wild birds, may result in increased exposures in some groups of people, particularly poultry workers, for example. There is existing federal guidance around bird flu exposures for different groups of people, including hunters, poultry producers and the general public, as well as health care providers. As a reminder, it is safe to eat properly handled and cooked poultry in the United States. The proper handling and cooking of poultry and eggs to an internal temperature of 165˚F kills bacteria and viruses, including HPAI A(H5) viruses.
Wild birds can carry HPAI A(H5) viruses without showing symptoms, but these viruses can cause illness and death in domestic poultry. Human infections with HPAI A(H5) bird flu viruses are rare but can occur, usually after close contact with infected birds. No human infections with highly pathogenic avian influenza A viruses have been detected to date in the United States. (There have been four human infections with low pathogenic avian influenza A viruses identified in the United States since 2002. The designation of pathogenicity is related to severity of illness in poultry not people.)
On the animal health side, the U.S. Department of Interior and USDA are the lead federal departments for outbreak investigation and control in wild birds, and USDA APHIS is the lead agency for such activities in domestic birds. This situation remains primarily an animal health issue, though CDC will support efforts to conduct surveillance among people with occupational or recreational exposures based on USDA and CDC guidances.
According to USDA APHIS, genetic sequencing and real-time RT-PCR laboratory testing performed on some of the virus samples collected from infected wild birds show the viruses are HPAI A(H5N1) bird flu viruses from clade 18.104.22.168b. CDC has an existing A(H5) candidate vaccine virus (CVV) whose hemagglutinin (HA) is genetically nearly identical to the A(H5) HA of viruses detected in North American wild birds and that could be used to produce vaccine for humans if needed. Sequencing data to date also suggests these viruses would be susceptible to current antiviral medications used to treat influenza. CDC will continue to monitor those viruses and update the vaccine virus if warranted.
Ancestors of these HPAI A(H5N1) viruses first emerged in southern China and led to large poultry outbreaks in Hong Kong in 1997, which resulted in 18 human infections. The outbreak was controlled, but the HPAI A(H5N1) virus was not eradicated in birds and re-surfaced in 2003 to spread widely in birds throughout Asia, and later in Africa, Europe, and the Middle East, causing sporadic human infections. HPAI A(H5) viruses were detected in North America in 2014 causing widespread poultry outbreaks and wild bird mortality events in Canada and the United States before disappearing in 2016.
Since 2003, 19 countries have reported 864 human infections and 456 deaths with HPAI A(H5N1) virus to the World Health Organization (WHO) as of January 21, 2022. The most recent human infection with HPAI A(H5N1) virus was reported in the United Kingdom in January 2022 in association with exposure to domestically kept infected birds.
Infected birds shed avian influenza A viruses in their saliva, mucous and feces. Human infections with bird flu viruses can happen when enough virus gets into a person’s eyes, nose or mouth, or is inhaled. People with close or prolonged unprotected contact with infected birds or contaminated environments may be at greater risk of infection. Illnesses in humans from avian influenza A virus infections have ranged from mild (e.g. eye infection, upper respiratory symptoms) to severe illness (e.g. pneumonia) resulting in death. The spread of avian influenza A viruses from one sick person to another is very rare, and when it has happened, it has not led to sustained spread among people.
While CDC considers the current risk to the general public from these HPAI A(H5) virus detections in U.S. wild birds and poultry to be low, risk depends on exposure, and people with more exposure may have a greater risk of infection. Sporadic human infections with HPAI A(H5) bird flu viruses in the U.S. resulting from close contact with infected birds/poultry would not be surprising given past human infections that have occurred sporadically in other countries and would not significantly change CDC’s risk assessment. However, if human-to-human spread with this virus were to occur, that would raise the public health threat. Note that sustained human-to-human spread is needed for a pandemic to occur.
CDC is working closely with USDA to monitor the current HPAI A(H5) virus situation and review existing guidance to determine if updates are needed. CDC will continue its ongoing assessment of the risk posed by these viruses, including conducting laboratory experiments to further characterize the virus. CDC will provide updates on this situation as needed.
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