Wednesday, November 09, 2022

USDA/APHIS Snapshot: HPAI H5N1 In The United States


#17,113

Over the past 10 days, Iowa - which had already lost more than 6 million birds in 2022  due to avian flu - has reported new outbreaks of H5N1 in poultry farms which will require the culling of more than 2 million additional birds. 



The avian epizootic of 2022 either has, or shortly will, eclipse the record setting outbreak of 2014-15, but in many ways, is already more impactful.  The previous outbreak only involved 15 states, saw relatively few wild birds affected, and ended abruptly once summer arrived. 

The 2022 outbreak has affected nearly the entire continental United States (and Alaska), has killed millions of wild birds, persisted throughout the summer, and has spilled over into a number of mammalian species (including at least 1 human). 

While the number of wild birds lost to HPAI will never be known, already the USDA/APHIS has confirmed more than 3,375 outbreaks across 46 states. 


Aside from its enhanced carriage by migratory birds, and an extended avian-host range (see DEFRA: The Unprecedented `Order Shift' In Wild Bird H5N1 Positives In Europe & The UK), the past two years has seen a steep increase in the number of `spillover events' to mammals by H5N1. 

A few examples include:


New this month, the USDA has added a dashboard tracking mammalian infections with HPAI H5, which already includes 78 events in the United States.

2022 Detections of Highly Pathogenic Avian Influenza in Mammals
Last Modified: Nov 2, 2022
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Learn more about 2022 detections of HPAI in Commercial and Backyard Flocks and HPAI in Wild Birds


There are many species that are potentially susceptible to HPAI. In addition to birds and poultry, H5N1 viruses have been detected in some mammals (see list below). Infection may cause illness, including severe disease and death in some cases.

Avian influenza is caused by influenza Type A virus (influenza A). Avian-origin influenza viruses are broadly categorized based on a combination of two groups of proteins on the surface of the influenza A virus: hemagglutinin or “H” proteins, of which there are 16 (H1-H16), and neuraminidase or “N” proteins, of which there are 9 (N1-N9). Many different combinations of “H” and “N” proteins are possible. Each combination is considered a different subtype, and related viruses within a subtype may be referred to as a lineage. Avian influenza viruses are classified as either “low pathogenic” or “highly pathogenic” based on their genetic features and the severity of the disease they cause in poultry. Most viruses are of low pathogenicity, meaning they causes no signs or only minor clinical signs of inflection in poultry.



HPAI H5 Clade 2.3.4.4b continues to evolve and spread globally. It has become better adapted to year-round persistence (see Study: Global Dissemination of Avian H5N1 Clade 2.3.4.4b Viruses and Biologic Analysis Of Chinese Variants), and has shown an increasing ability to spillover into mammalian species.

Despite 4 known (mild) human infections, the health threat to the general public from these viruses remains very low, and it is mainly of concern to those who work closely with poultry. 

Low doesn't mean zero, however.  Which is why the CDC has issued guidance for the public On Preventive Measures to Protect Against Bird Flu Viruses. 

But even if HPAI H5 remains only a threat to poultry and wild birds (and the occasional fox, or seal), it could still have a big impact on the cost of poultry and eggs this winter, and large culling operations could put thousands of farmers (and their employees) into financial jeopardy.

Stay tuned. The traditional `high season' for avian flu is just getting underway.
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