Time to wake up to the threat of Zoonotic diseases | Daily News


Predicting pandemics:

Time to wake up to the threat of Zoonotic diseases

Dennis Carroll doesn’t mean to sound callous when he says the Coronavirus outbreak was predictable. And he doesn’t. He sounds sympathetic to people frightened by the outbreak. He has been an eyewitness to people around the world suffering from similar viruses. Most of all, Carroll sounds authoritative.

For decades, Carroll has been a leading voice about the threat of Zoonotic spillover, the transmission of pathogens from nonhuman animals to us. Scientists are confident the current outbreak, which began in Wuhan, China, stemmed from a virus inherent in bats. In 2009, after years of studying infectious diseases at the Centers for Disease Control and Prevention, and the United States Agency for International Development (USAID), Carroll formed a USAID programme called PREDICT, where he guided trailblazing research into viruses hiding, and waiting to emerge, in animals around the world.

In conversation, scientific insights, based on his experience, emerge from Carroll with a sting, whether he’s talking about the biology of viruses or the stagnant response to the outbreak from the White House.

How did the current Coronavirus pass from a bat to humans?

We don’t know specifically, but presumably the virus was being shed by the animal in the market, and humans were proximal. Or it could have been that people were directly handling the animal. There may have been a secondary source. In the 2002 SARS outbreak in China, we didn’t see people’s direct exposure to bats as the source of infection. There was a secondary source, a wildlife animal, the civet cat.

Could the transmission have resulted from people eating the wildlife?

Typically the preparation of the animal is where you have exposure. By the time it’s cooked and prepared, the virus would have been dead. It’s more common that transmission is through the animal shedding or people slaughtering the animal, when they’re exposed to bodily fluids, blood, and secretions. With the avian influenza from poultry, a lot of the exposure and infections go back to the preparation of chicken for cooking.

In 2018, you and colleagues wrote in Science, “Our ability to mitigate disease emergence is undermined by our poor understanding of the diversity and ecology of viral threats.” What do we need to understand about the diversity and ecology of viral threats?

The first thing to understand is that whatever future threats we’re going to face already exist; they are currently circulating in wildlife. Think of it as viral dark matter. A large pool of viruses is circulating and we don’t become familiar with them until we see a spillover event and people getting ill.

Do bats have a particularly high potential for spillover?

Certainly. We’ve been able to identify bats as reservoirs for Coronaviruses and documented specific bat populations as reservoirs for Ebola virus. We want to understand how each of these bats operate within an ecosystem. Do they have certain behaviours and practices that either keep them remote from or proximal to human populations? The bat population in which we isolated the Ebola virus in West Africa was a species of bat that also tends to co-roost within human housing, so it elevates the opportunity for spillover.

Have there been disturbances in their environments that have brought bats closer to us?

The disturbances in their environments are us. We’ve penetrated deeper into ecozones we’ve not occupied before.

What’s a telling example of our incursion?

In Africa, we see a lot of incursion driven by oil or mineral extraction in areas that typically had few human populations. The problem is not only moving workers and establishing camps in these domains, but building roads that allow for even more movement of populations. Roads also allow for the movement of wildlife animals, which may be part of a food trade, to make their way into urban settlements. All these dramatic changes increase the potential spread of infection.

Are spillover events more common now than 50 years ago?

Yes. EcoHealth Alliance, an NGO, and others, looked at all reported outbreaks since 1940. They came to a fairly solid conclusion that we’re looking at an elevation of spillover events two to three times more than what we saw 40 years earlier. That continues to increase, driven by the huge increase in the human population and our expansion into wildlife areas. The single biggest predictor of spillover events is land-use change—more land going to agriculture and more specifically to livestock production. I’m stunned by the absolute absence of global dialogue for what is a global event.

Is there something specific about a virus that makes it zoonotic?

You can argue viruses aren’t living organisms. They’re sheets of proteins encapsulating some DNA or RNA. Beyond that, they have no machinery to be able to live on their own. They’re looking for an ecosystem that has all of the other cellular machinery essential for replication. They can’t live outside another animal population. They need that animal to replicate. And we’re just one more animal. We think of ourselves as something special. But viruses are infecting us with exactly the same purpose they infect a bat or a civet cat.

Viruses live on a delicate balance, don’t they? They have to be able to thrive without killing their host.

Right. The ones that kill off their host quickly will disappear. With the SARS virus, it’s no surprise that killing 10 percent of its host, it wasn’t able to establish itself as a pandemic virus on this planet.

Are there any signs that this Coronavirus will kill itself?

This one has a lower pathogenicity. The lower its virulence, the more likely it’ll become part of an endemic, part of a seasonal event. That’s one of the big things that’s going to be a worry. If it does go quiet over the summer months, then the question’s going to be, “Is it still infecting people?” We could be walking around in the middle of summer with influenza viruses, but they’re not active. They’ve just gone quiet. When the right ecology comes into play, it starts getting cold, and damp, then it starts replicating like crazy. If it’s able to park itself, and not kill its host over the summer months, then we’ve got a virus that has all the telltale signatures of establishing itself as part of our normative landscape, much to our detriment.

Do you think the current outbreak was inevitable?

Oh, sure. It was predictable. It’s like if you had no traffic laws and were constantly finding pedestrians getting whacked by cars as they crossed the street. Is that surprising? No. All you need to do is to better manage how we set up crosswalks, how we establish traffic rules and regulations. We’re not doing that. We’re not establishing the kind of safe practices that will minimize the opportunity for spillover. If we better understood where these viruses are circulating and understood that ecology, we would have the potential to disrupt and minimize the risk of spillover.

Why aren’t we—governments and policymakers—doing that?

First, this is an expanding problem driven by unprecedented population change. It’s only in the last 100 years that we’ve begun adding people at a rate that’s causing this incredible disruption of the larger ecosystem. If you and I were having this discussion 100 years ago, there were 6 billion fewer people on this planet. It took us the better part of our total existence of the species, 300,000 years, before we hit the 1 billion mark. But in 100 years we’ve added 6 billion people and we’ll add another 4 to 5 billion before the end of this century.

Second, governments and society by and large are governed by inertia. We don’t change and adapt and evolve very quickly. And we’re barely cognizant as a global society that the world we’re living in today is fundamentally different than the world our species has ever lived in. You know that old saying that if you drop a frog in a pot of boiling water, it will leap out. But if you take that same frog and put it in a pot of ambient water and slowly crank up the temperature, it will stay in that water and boil to death. It loses perspective on the changing environment around it. We’re that frog in the ambient water. We are oblivious to the conditions that have enabled zoonotic viruses to become integrated into us.

What first really opened your eyes to the scale of the spillover problem?

It was avian influenza in the 2000s. What you saw with avian influenza was a direct consequence of how much poultry was being produced to feed people. If you look at China today, it produces something on the order of 15 to 20 billion poultry per year. But if you went back and you looked at the data from the 1960s, you see that, at best, only a few hundred million poultry were under production. When you look in Bangladesh, Vietnam, and elsewhere in Asia and Indonesia, you see that the amount of poultry that was being produced 50 years ago was orders of magnitude less than poultry being produced today. That’s a consequence of more people and more purchasing power. One of the things we know about household purchasing power is that when you have disposable income in your hands, you’re going to move from a root- or grain-based diet and try to get animal protein. And that’s what happened.

One statistic that jumps out of what you wrote in Science is there are 1.67 million viruses on Earth and an estimated 631,000 to 827,000 have the capacity to infect people. That’s pretty frightening, no?

On one level it is pretty frightening. But on another level the potential to infect doesn’t necessarily correlate with illness and death. Some viruses may not have any consequence at all. And some may be involved in enhancing our own biology. They could become part of our microbiome. It’s nothing new in the course of evolution. We have to be open to the idea that viruses aren’t simply our enemies, that they may have an important and positive role to play for us. We found that out about bacteria. At the same time, we have to keep our eyes open and be cautious about the pharmaceuticals we take. If we’re taking broad-spectrum antivirals, they could be opening up other complications.

How would you describe the general attitude of governments toward the threat of zoonotic diseases?

It’s not just the U.S. government but governments at large and the private sector—we don’t invest in risk. Talking about zoonotic diseases is different than talking about tuberculosis or malaria. Those are tangible. They are clear and present problems. Zoonotic diseases are an emerging problem. But we as a society don’t invest in things that are not kicking our door down.

The Coronavirus is kicking our door down now, don’t you think?

Yes, it’s got everyone’s attention. But this Coronavirus will fall off the headlines and when it does, you will see a contraction in the kind of investments that are made in it. We have war budgets and then no monies during peacetime. So part of the challenge—it’s a social engineering exercise—is getting lawmakers and investors to invest in risk. That’s really difficult.



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