The Taming of Influenza

Darwin and the domestication of germs

Published on February 26, 2013by Lauren Weisenfluh

As far as influenza outbreaks go, experts agree: The current influenza outbreak is not bringing its A game. It is not particularly virulent—capable of causing disease. It doesn’t even hold a candle to the 1918 Spanish influenza, known as the mother of all pandemics, which killed 50 million people.

Yet, it is still making headlines for surpassing epidemic levels in 47 states, overwhelming our healthcare system and shutting down hospitals.

We are losing the never-ending influenza arms race. Less than half of all Americans are vaccinated against the flu every year. Influenza strains are evolving resistance to antiviral treatment. And even so, antivirals are increasingly used to prevent the spread of influenza outbreaks without understanding their consequences.

It is time for a new management approach—an evolutionary approach.

Since the discovery of antivirals and antibiotics, our focus has shifted dramatically away from disease prevention and towards treatment. Rather than pre-emptively getting the flu vaccine every year, many risk the flu gamble, treating the flu with antivirals if ensnared. As a result, levels of antiviral resistance have increased, launching an arms race between pathogens and people, as pathogens become increasingly virulent.

It doesn’t have to be this way. In fact, Darwinian theory suggests that a focus on simple preventative public health barriers—such as condoms, clean water, and infection-blocking vaccines—rather than treatment, can domesticate pathogens towards milder virulence.

We can domesticate influenza, much as we have domesticated cats, dogs, and sheep for centuries. We just need to select for the traits that we want by understanding and incorporating the evolutionary trade-off between virulence and transmission.

The idea marries the fields of evolutionary ecology and epidemiology, and was first presented by Dr. Paul Ewald, director of the Evolutionary Medicine department at the Biology Department of University of Louisville, in 1995.

Evolution clearly has a bad rap in the media. We are told that because of our actions, because we don’t finish our antibiotics or take antibiotics when we don’t need them, germs are evolving towards unconquerable levels and becoming superbugs: the ultimate microbial foes.

But manipulation goes both ways. We can wield our power for good.

That is what Dr. Ewald found when he visited South America in 1991 during a cholera outbreak. A highly virulent form of cholera was spreading through the water, making its victims very sick.

But when people sanitized their water, cholera evolved towards mild virulence.

The explanation becomes clearer from the bug’s point of view. It faced a challenge: When water is sanitized, it can no longer jump to its next victim using water as its microbial trampoline. It has to use human hosts. And because rendering its human host bed-ridden decreases its opportunities to jump to another human, cholera rapidly evolved towards mild virulence.

Without the water, it was forced to co-exist with its human host.

We see a similar pattern that could explain the extreme virulence of the 1918 influenza pandemic. Trench warfare in World War I put sick soldiers into close quarters. Even when soldiers’ influenza laid them up, cramped field hospitals and tents became the close-quartered trenches of sick soldiers. This allowed the highly virulent influenza to travel through air droplets from human to human, even without a moving host.

This would suggest that without immobile hosts, it is highly unlikely that influenza would evolve towards virulence levels reminiscent of the 1918 influenza.

While this idea in itself is indeed a simplification of the complex dynamics affecting natural selection, it does pose some interesting ideas. For example, the investment in public health interventions vis-à-vis environmental control, rather than flu antivirals, would be a better management approach of influenza.

This idea is not new, nor is debate surrounding it. Scientists have long quarreled over the roots of successful disease management. In the 1950s-1970s, a demographer named Thomas McKeown stirred up controversy, suggesting that food supply, population growth, and economic advances—not advances in public health sanitation—were responsible for the demographic transition from infectious to chronic disease.

While the hypothesis was eventually debunked, it remains a reminder that disease management is a controversial subject, even when simple, economical, and effective public health measures are involved.

Meanwhile, our treatment arms race with influenza continues. It is a race that we are losing, and a battle that is all too familiar in this day and age.

But we haven’t lost the battle yet. We still can take the evolutionary approach, even if it will evoke historical debates. But if Darwin was even remotely correct, and if simple public health preventive measures can tame influenza—it means that we need a dramatic change in disease management, shying away from treatment and towards prevention.

It is Darwinian change we can believe in, for the sake of the public’s health.

Edited by Dana March. Additional research by Joshua Brooks.