Spillover: Animal Infections and the Next Human Pandemic

by David Quammen

“It was striking because I couldn’t find any lymphocytes,” she told me. “When I saw the first lymph node, I thought, ‘Hmm, this is weird.’

“We have a problem,” Terio told Lonsdorf. “She doesn’t have any lymphocytes.” “Does that mean what I think it means?” “Yes. The lesions in this animal look like an end-stage AIDS patient.”

The chimp Yolanda, dead at age twenty-four, had been SIV-positive and suffering immune deficiency.

That the AIDS pandemic is traceable to a single contingent event. That this event involved a bloody interaction between one chimpanzee and one human. That it occurred in southeastern Cameroon, around the year 1908, give or take. That it led to the proliferation of one strain of virus, now known as HIV-1 group M. That this virus was probably lethal in chimpanzees before the spillover occurred, and that it was certainly lethal in humans afterward. That from southeastern Cameroon it must have traveled downriver, along the Sangha and then the Congo, to Brazzaville and Léopoldville. That from those entrepôts it spread to the world.

injection campaigns could have played a role later, spreading the virus in Africa once it was established.

Marx’s group even argued that serial passage of HIV through people, by means of such injection campaigns, might have accelerated the evolution of the virus and its adaptation to humans as a host, just as passaging malarial parasites through 170 syphilis patients (remember the crazed Romanian researcher, Mihai Ciuca?) could increase the virulence of Plasmodium knowlesi.

Pepin’s main point was simply that dirty needles, used so widely, must have increased the prevalence of the virus among people in Central Africa.

Their data and analysis indicated that just a single migration of the virus—one infected person or one container of plasma—accounted for bringing AIDS to America. That sorry advent occurred in 1969, give or take about three years.

This virus was patient, unlike Ebola, unlike Marburg. More patient even than rabies, but equally lethal.

Outbreak in the broader sense applies to any vast, sudden population increase by a single species.

What makes a species of insect—or of mammal, or of microbe—capable of the outbreak phenomenon? That’s a complicated question that the experts are still trying to answer.

From the ecological point of view an outbreak can be defined as an explosive increase in the abundance of a particular species that occurs over a relatively short period of time.”

“From this perspective, the most serious outbreak on the planet earth is that of the species Homo sapiens.” Berryman was alluding, of course, to the rate and the magnitude of human population growth, especially within the last couple centuries. He knew he was being provocative.

So we’re unique in the history of mammals. We’re unique in the history of vertebrates. The fossil record shows that no other species of large-bodied beast—above the size of an ant, say, or of an Antarctic krill—has ever achieved anything like such abundance as the abundance of humans on Earth right now.

Like, the virus doesn’t cause the insect to explode,” he insisted. “It causes it to melt.”

The Analogy. As of last week, I said, we’ve got 7 billion humans on this planet. It seems like an outbreak population. We live at high densities.

Okay so far? Having absorbed this simple paragraph, you understand more about influenza than 99.9 percent of the people on Earth. Pat yourself on the back and get a flu shot in November.

Sure, Graeme Laver made the discovery that waterfowl are the reservoirs of influenza, with my help. Laver by now was dead, but fondly remembered by Dr. Webster.

“Are we all gonna die?” I have made it my little policy to say yes. Yes, we are all gonna die. Yes. We are all gonna pay taxes and we are all gonna die. Most of us, though, will probably die of something more mundane than a new virus lately emerged from a duck or a chimpanzee or a bat.

Lol

(1) Will a new disease emerge, in the near future, sufficiently virulent and transmissible to cause a pandemic on the scale of AIDS or the 1918 flu, killing tens of millions of people? and (2) If so, what does it look like and whence does it come?

“The second criterion is proven ability to cause major epidemics in non-human animal populations.” This would again spotlight the orthomyxoviruses, but also the family of paramyxoviruses, such as Hendra and Nipah, and the coronaviruses, such as that virus later known as SARS-CoV.

Burke’s third criterion was “intrinsic evolvability,” meaning readiness to mutate and to recombine (or reassort), which “confers on a virus the potential to emerge into and to cause pandemics in human populations.” As examples he returned to retroviruses, orthomyxoviruses, and coronaviruses.

“Some of these viruses,” he warned, citing coronaviruses in particular, “should be considered as serious threats to human health. These are viruses with high evolvability and proven ability to cause epidemics in animal populations.” It’s interesting in retrospect to n...

By “the scientific basis” he meant the understanding of which virus groups to watch, the field capabilities to detect spillovers in remote places before they become regional outbreaks, the organizational capacities to control outbreaks before they become pandemics, plus the laboratory tools and skills to recognize known viruses speedily, to characterize new viruses almost as fast, and to create vaccines and therapies without much delay.

we can be well-prepared and quick to respond; we can be ingenious and scientifically sophisticated in the forms of our response.

Because of concern over the potential of “bioterrorism,” even the US Department of Homeland Security and the Defense Advanced Research Projects Agency (aka Darkest DARPA, whose motto is “Creating & Preventing Strategic Surprise”) of the US Department of Defense have their hands in the mix.

Private organizations, such as EcoHealth Alliance (led by a former parasitologist named Peter Daszak and now employing Jon Epstein for his Nipah work in Bangladesh and elsewhere,

When the next novel virus makes its way from a chimpanzee, a bat, a mouse, a duck, or a macaque into a human, and maybe from that human into another human, and thereupon begins causing a small cluster of lethal illnesses, they will see it—we hope they will, anyway—and raise the alarm. Whatever happens after that will depend on science, politics, social mores, public opinion, public will, and other forms of human behavior. It will depend on how we citizens respond.

We should appreciate that these recent outbreaks of new zoonotic diseases, as well as the recurrence and spread of old ones, are part of a larger pattern, and that humanity is responsible for generating that pattern.

Ecological circumstance provides opportunity for spillover. Evolution seizes opportunity, explores possibilities, and helps convert spillovers to pandemics.

They remind us, as St. Francis did, that we humans are inseparable from the natural world. In fact, there is no “natural world,” it’s a bad and artificial phrase. There is only the world. Humankind is part of that world, as are the ebolaviruses, as are the influenzas and the HIVs, as are Nipah and Hendra and SARS, as are chimpanzees and bats and palm civets and bar-headed geese, as is the next murderous virus—the one we haven’t yet detected.

How much does it matter that humans are smart? And so, I guess I’m actually going to say that it matters a whole lot. Now that I stop to think about it carefully. I think it will matter a great deal.”