Credit USDA
#16.561
The HPAI H5 virus that sparked the avian epizootic across much of Canada and the United States in 2015 was a less-evolved ancestor of today's HPAI H5N1 virus; one that is severely impacting poultry interests in Europe and has recently arrived in North America.
Following the 2015 epizootic all traces of that H5Nx virus vanished in American birds within a few months (see PNAS: The Enigma Of Disappearing HPAI H5 In North American Migratory Waterfowl).
Over the past 6 years, however, we've seen a steady increase in H5Nx clade 2.3.4.4b's host range, and pathogenicity, following a reassortment event in either Russia or China over the summer of 2016 (see EID Journal: Multiple Reassorted Avian H5N8 Viruses In The Netherlands, 2016).
While it kills many wild bird species, it can now also be carried asymptomatically by others.
Still, this Eurasian H5Nx (H5N1, H5N6, H5N8, etc.) is considered to pose far less of a threat to human health than the Asian H5N1 and H5N6 viruses, which have caused hundreds of deaths over the past couple of decades.
That said, all of these viruses share a common ancestor, and all viruses continue to evolve. So we can't rule out the possibility that this EA H5N1 virus might someday pose a bigger threat.
And its recently acquired ability to persist in some migratory bird species suggests we may see this virus return to North America on a more regular basis in the future.
While the threat to human health today is admittedly very low, the CDC has issued the following statement that outlines the potential risks - both now - and in the future.
Recent Bird Flu Infections in U.S. Wild Birds and One Poultry Facility Pose a Low Risk to the Public
This is a picture of an American widgeon in flight. In mid-January, USDA first announced finding highly pathogenic avian influenza (HPAI) A(H5) bird flu virus in wild birds, marking the first detection of this virus in wild birds in the United States since 2016. This was followed by an announcement of an outbreak of HPAI in commercial poultry on February 9, 2022.
February 9, 2022—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 pdf icon[532 KB, 2 Pages], 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 2.3.4.4b. 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.
For more background on the evolution of HPAI H5Nx, and its increasing zoonotic threat, you may wish to revisit:
ECDC/EFSA Raised the Zoonotic Risk Potential Of Avian H5Nx
