Health Policy

Global Warming and Disease


A study eight years ago, published in Nature, was titled “Study revives bird origin for 1918 flu pandemic.” The study, which analyzed more than 80,000 gene sequences from flu viruses from humans., birds, horses, pigs, and bats, concluded the 1918 pandemic disaster “probably sprang from North American domestic and wild birds, not from the mixing of human and swine viruses.”

The search for origin in pandemics is not simply an esoteric academic exercise. It is practical, pragmatic, and hopefully preventive. The origin of our very own pandemic, now in its third year and claiming more than 1 million American lives, remains up in the air. Whether occurring “naturally” from an animal reservoir, or the progeny of an experimental lab engaged in U.S. funded “gain-of-function” research, we may never know. What we do know is that viruses move at the speed of light, or more accurately, at the speed of birds.

When Tippi Hedren and Rod Taylor headed indoors at Bodega Bay, California in a high-speed attempted escape from sudden violent bird attacks in the Alfred Hitchcock 1963 natural horror-thriller film, The Birds, it was beaks not bugs they were trying to avoid. But sixty years later, we may all soon find ourselves nodding in agreement with the Library of Congress which declared Hitchcock’s work to be “culturally, historically, and aesthetically significant.”

Last month’s Nature publication, written by science journalist Brittney J. Miller, titled “Why unprecedented bird flu outbreaks sweeping the world are concerning scientists,” raised the alarm. As she writes “Mass infections in wild birds pose a significant risk to vulnerable species, are hard to contain and increase the opportunity for the virus to spill over into people.”

In the past 9 months, an H5N1 bird flu strain has ignited 3,000 outbreaks in domestic poultry populations across the globe – from Europe, Asia, Africa, and North America. Local governments have limited the damage by destroying (culling) over 77 million birds. But these chickens and turkeys don’t fly commercial, so how did their virus spread?

The answer lies in the dead bodies of another 400,000 wild birds, mostly water fowl, involved in another 2,600 outbreaks in 2022. So far, the virus doesn’t seem to like humans much. Only two human cases (one in the U.K. and another in the U.S.) have been flagged. But spillover, say experts, is inevitable with spread at this rate. A WHO representative says, “These viruses are like ticking time bombs. Occasional infections are not an issue – it’s the gradual gaining of function of these viruses” that’s makes everyone nervous.

Since 1996, wild birds have been in the cross-hairs. Back then, a pathogenic H5N1 bird flu appeared in geese in Asia. Within 5 years, it was all over Europe and Africa. Five years later, widespread mass deaths of wild birds appeared tracked back to the original geese. Within another 10 years, a worrying trend evolved. A strain throughout North America appeared that infected a range of wild birds but didn’t always kill them. For example, mallard ducks were routinely infected, but only 10% died. While good for the ducks, their survival fueled continued spread and reengineering through mutation of the virus.

As you might imagine, it’s not as easy to track and monitor wild birds as well as cooped up chickens. Nor is killing them in masse once infected a reasonable, or achievable option. From the wild bird’s perspective, these are not the best of times. If you are a ruddy turnstone or a resident duck on the Delaware Bay, things are heating up in more ways than one. 

Global warming is affecting the timing of horseshoe crab spawning season at the Delaware Bay. 

The northern Arctic migration (with a stopover at the Delaware Bay) of the ruddy turnstone (which feeds on the crab) has been prolonged as a result. Many of these birds are bird flu carriers. The longer they hang around, the more they infect the local water fowl residents – especially, ducks, swans, geese, shorebirds, and waders. On top of this, when the ruddy turnstone and other migrators reach the Arctic, they are staying longer thanks to moderating temperatures and ice melting. Scientists have concluded that “these conditions support maximal transmissions (of viruses) across wild water birds.”

Climate change not only leads to northward shifts, but expanded species diversity, accompanied by shorter migratory routes. Both spell greater mixing and exchange of viruses across avian species. Spring migrations are now taking place earlier, with age classes, species and flyways significantly altered. Extreme climatic events, more common in an age of “global weirding” of weather, are also more common. For example, a cold clip near the Caspian Sea in 2006 triggered a mass exodus of swan, which unleashed an H5N1 viral outbreak in domestic birds across Western Europe.

What ecologists are saying is that “A1 viruses have co-evolved with migratory waterfowl over millions of years and have survived and withstood many eras of climatic turbulence… An increase in the proportion and number of birds over-wintering in the subarctic areas may result in very high densities of birds competing for the limited feed resources available. This could potentially enhance interspecies virus transmission, involve a larger spectrum of avian host species or alter the virus transmissibility, both to wild birds and domestic poultry.”

As more and more Canadian geese set up permanent domicile in the grassy wonderlands of suburban America, they and their wild avian friends are increasingly settled in, crowding together in a new world, permanently residing in intimate contact with humans. The shrill alarms set off by environmental scientists have now been joined and reinforced by an increasingly alarmed global infectious disease community.