The US is experiencing its largest avian influenza outbreak ever. This is contributing to the rising cost of food and is a reminder that the health of wildlife, domesticated animals and livestock, and humans are deeply intertwined. Scientists call this interconnectedness “One Health”.
Of particular interest this week is the fact that avian influenza, or “bird flu”, is driving up the cost of Thanksgiving turkeys. My forbes.com colleague and fellow scientist, Bruce Y. Lee, reported three days ago that Thanksgiving turkeys are still up about 20% compared with last year, and this is down from a high of 73% a few months ago, at least partly because retailers have chosen to absorb the difference.
Where did avian influenza come from?
Avian influenza is not new. In fact, wild birds are the primary reservoir of most influenza viruses. Over the last century, new human influenza viruses have emerged on four separate occasions — in 1918, 1957, 1966, and 2009 — when avian influenza viruses “reassorted” with human ones.
Because novel human influenza viruses arise relatively rarely, one might think that bird flu itself is rare. But, this is not the case. Avian influenza affects a wide range of wild bird species, from ducks and geese to gulls and waders.
One study found that the prevalence of influenza antibodies — a measurement of past infections — in laughing gulls (Leucophaeus atricilla) ranged from 25%–72%. In some places, the prevalence of influenza in wild birds has been known to approach 50%.
Most of this influenza is known as Low Pathogenic Avian Influenza (LPAI). LPAI rarely causes symptomatic disease, in contrast to Highly Pathogenic Avian Influenza (HPAI). While LPAI is around nearly all the time, HPAI tends to be more episodic and prone to dramatic outbreaks.
Like LPAI, HPAI viruses are carried by wild birds. But, unlike LPAI, when HPAI gets into poultry it spreads rapidly from bird to bird causing outbreaks that can be devastating to commercial flocks.
Outbreaks of Highly Pathogenic Avian Influenza
North America is currently in the middle of its largest outbreak of HPAI since 2014-2015, when approximately 7 million turkeys and 43 million chickens were lost through disease or “depopulation”, a USDA policy and containment strategy that requires culling all birds on affected premises. The 2014-2015 outbreak is estimated to have cost taxpayers $879m in public expenditures, a figure that does not include uncompensated costs to producers, making the 2014-2015 HPAI outbreak the most costly animal health incident in US history.
Now, the current outbreak appears poised to surpass these figures. According to the CDC, as of November 22, 2022, a total of 50,461,200 birds have been affected — more or less tied with the 2014-2015 total. Although the outbreak is slowing down (it appears to have peaked in September and October), additional infected flocks are being detected almost every day.
Counties reporting avian influenza criss-cross the US ranging from Florida to Washington and California to Maine. Only the states of Alabama, Hawaii, Louisiana, and West Virginia have not reported infections. The places where infected birds have been found include backyards, petting zoos, production facilities for game birds, and the farms of commercial breeders of turkeys, ducks, and chickens.
So far, only one case has been reported in a human. This was in a person who was treating birds that were believed at the time to be infected. Even though the CDC considers the threat to the general public to be low, government officials nonetheless urge people raising chickens in their backyards to take precautions such as using gloves and face masks or respirators when handling birds, washing their hands after touching birds, and avoiding direct contact with clothing or other materials that may have become contaminated with animal saliva, mucous, of feces.
A one health approach to influenza
All of this is a reminder that human health and animal health are linked. Zoonoses are pathogens of animals transmitted to people and there is evidence that zoonoses are increasing in frequency. In 2020, The United Nations Environment Programme issued a report warning that more events like the Covid-19 pandemic are to be expected unless actions are taken soon to mitigate the spillover of animal pathogens into people. This is the idea of One Health, about which I have written before. Our human population and that of the other species with which we share the planet are deeply connected. Our fates rise and fall together. The high price of holiday turkeys right now is a reminder of that fact.