Worst of Both Worlds

Evolutionary jackpot

Increasing outbreaks among chickens over the past decade have seemed to go hand-in-hand with increasing human transmissibility in both high- and low-grade bird flu viruses. A decade ago, human infection with bird flu was almost unheard of. Now, H5N1 is just one of five chicken viruses that have jumped the species barrier to people. H9N2 infected children in China in 1999 and 2003; H7N2 was found infecting persons in New York and Virginia in 2002 and 2003; and H7N3 infected poultry workers in Canada in 2004.³⁰²² After H5N1, though, the largest outbreak of bird flu in history was the 2003 disaster in the Netherlands.

One of the most densely populated countries in the world, the Netherlands squeezes 16 million people, 11 million pigs, and more than 90 million poultry³⁰²³ into a country no more than twice the size of New Jersey.³⁰²⁴ Little surprise, then, that such conditions fostered the bird flu epidemic that led to the deaths of an unprecedented (at the time) 30 million birds.³⁰²⁵

A shocking government report released the following year revealed that the outbreak of H7N7 in the Netherlands had not only infected more than 1,000 people,³⁰²⁶ but the virus had passed from human to human. Symptomatic poultry workers passed the virus to a “whopping” 59% of their household family members.³⁰²⁷ Fortunately, only one person died—a veterinarian involved in the cull.³⁰²⁸ It was a relatively wimpy virus, typically causing, at most, mild flu symptoms. Dutch experts realize, though, how close their poultry industry came to potentially preempting H5N1 by sparking the next human pandemic. According to experts from the country’s National Institute of Public Health,

Although we launched a large and costly outbreak investigation (using a combination of pandemic and bioterrorism preparedness protocols), and despite decisions being made very quickly, a sobering conclusion is that by the time full prophylactic measures were reinforced…more than 1,000 people from all over the Netherlands and from abroad had been exposed. Therefore if a variant with more effective spreading capabilities had arisen, containment would have been very difficult.³⁰²⁹

Bird flu viruses previously required freak lab accidents to directly infect people; now this occurs with frightening and increasing regularity. There was an almost 80-year lag between the time when a wholly avian flu virus seemed to grow fatal in 1918 and when a bird flu virus acquired enough virulence to kill again in Hong Kong in 1997. Although industrial poultry production was invented in the 1950s, only within the last few decades has intensive production truly gone global. Shortridge concluded in the academic text Avian Influenza: Prevention and Control: “The intensification of the poultry industry worldwide seems to be a key element in causing influenza viruses of aquatic origin to undergo ‘more rapid’ adaptation to land-based poultry….”³⁰³⁰ We have dug WWI-type trenches for billions of birds all around the world.

With unprecedented numbers of chickens intensively confined at record density,³⁰³¹ we are seeing bird flu viruses adapt to humans in ways we’ve never seen before. The reason the 1918 virus killed fewer than 5% of its victims may have been because it was essentially restricted to the lungs. The spitting of blood and blackening of limbs was a result of the slow-motion drowning the virus triggered by choking the lungs with fluid. For H5N1, “It’s worse than that,” says Osterholm. “[I]t it also goes in and begins to shut down all your vital organs. It’s a domino effect. Your kidneys go down, then your liver goes down, you have all this destruction through necrosis of your lungs and your internal organs. Everything goes.”³⁰³² Never before has a bird flu virus learned to activate itself throughout the human body until H5N1.³⁰³³

By adapting to chickens, bird flu viruses hit an evolutionary jackpot. And by adapting to chickens, the viruses may be adapting to the human race—another multibillion-host bonanza for the virus.³⁰³⁴ But there need not be billions of chickens. We don’t need to keep restocking broiler and layer sheds. No scientist is naïve enough to think that humans will stop eating poultry or eggs in the near term—even if the worst-case scenario is one day realized, KFCs may very well be rebuilt with the rest of human civilization. Until, perhaps, the day chicken flesh can be safely grown economically in a lab,³⁰³⁵ humanity may continue to face influenza pandemics. Ending chicken consumption may be little more than a hypothetical, but ending the riskiest practices, the most intensive forms of industrial poultry production, seems an attainable goal.

With the emergence of H5N1, the fate and future of chickens is inexorably tied up with our own. The disease resistance of chickens may need to be considered a critical public health issue. No longer may chicken breeding remain a simple business decision of counting carcasses and seeing if the per-bird profits of the survivors compensate for the mortality. It may be a matter of global health how the industry breeds birds, or whether they should be breeding them at all.

Humanity may decide that eating chicken is worth weathering the occasional pandemic, but is cheaper chicken worth risking viruses like H5N1? The best that free-range poultry seem able to pull off appears to be the 1918 2.5% mortality, and it may have needed World War I as an accomplice to do it. As hard as it is to imagine a virus more ominous than H5N1, intensive poultry production on a global scale is a relatively new phenomenon. As poultry consumption continues to soar in the developing world, there is no biological reason that bird flu could not evolve and mutate into an even deadlier niche.

All pandemic precursor strains continue to exist in the natural waterfowl reservoir, lying in wait for an opportunity to break out.³⁰³⁶ As the New York Times put it, “Somewhere, in skies or fields or kitchens, the molecules of the next pandemic wait.”³⁰³⁷ H5N1 showed that chickens can breed a flu virus of unparalleled human lethality, and the Dutch H7N7 outbreak showed that chickens can produce a virus that directly jumps from human to human.³⁰³⁸ Even if H5N1 never develops the capacity to go pandemic, it may only be a matter of time before the new poultry factories of the world breed the deadliest of combinations.