Why are so many viruses popping up again?


Jay K. Varma is an internal medicine physician, epidemiologist and professor of population health sciences at Weill Cornell Medicine.

Q: It feels like viruses are all over the news, whether it’s monkeypox, Ebola, polio or the coronavirus. Are there more outbreaks now than usual?

A: Several factors help explain why we’re hearing so much about viral outbreaks. Shifts in migration and travel patterns, global eating habits and the effects of climate change have created new opportunities for microbes to spread. Better testing and monitoring methods also mean we’re detecting these outbreaks sooner than in the past.

What we’re experiencing right now is likely to become the new way we live, forcing us to adapt to a riskier world, much like we did after 9/11. We’ve accepted that we have new rules around air travel, security and identification to prevent terrorism. We’re also going to have to accept changes in how we live and cope in this era of emerging infectious diseases.

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Most infectious diseases that we consider “new” already exist in animals. Some animals don’t get sick from them but host them in their bodies. For example, the HIV epidemic started when humans came into contact with an animal (in this case, chimpanzees). The virus spilled over from chimpanzees into humans and began spreading from human to human. With HIV, that spillover likely occurred in the early 1900s, but it took decades until scientists realized it was killing people.

Our ability to detect new diseases through laboratory testing is getting better every day, so public health agencies are detecting new threats faster. But this doesn’t completely explain why so many new infections have emerged or why so many old infections, such as polio, have returned.

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What does explain it? One way to think about this is like a sports competition: The bacteria, viruses and other microscopic threats are playing offense, and the systems we’ve created to detect and respond to infectious diseases are playing defense. Over the past 20 years, the offense has gotten stronger, but our defense simply has not kept up.

Here are five reasons the microbes appear to be winning now.

Humans are encroaching into animal environments, such as forests and jungles, at a greater frequency. Research has shown that the highest-risk place for new diseases to emerge is at the edge of forests and jungles. The animals that survive and thrive there are also those most likely to carry infectious diseases that are dangerous to humans: rats and bats. (The coronavirus is an example of a virus that most likely originated in a bat.) Sometimes, the spillover is not direct but goes through an insect. For example, a tick or a mosquito bites an animal that picks up the infection, then it bites a human and passes the infection onto them, as with Lyme disease.

Covid, monkeypox, polio: Summer of viruses reflects travel, warming trends

Humans are growing, trading and consuming animals in greater numbers. As economies grow and lift people out of poverty, people want to eat more protein, which means a greater need to grow animals in large numbers and sell and ship them around the world. The more animals are concentrated together, the more likely a new disease is to spread among them, then spillover into humans, including through contamination of food or water. New drug-resistant “superbugs,” such as strains of salmonella, often arise this way.

Humans are concentrating in cities more than ever before. If you want a disease to spread person-to-person, there’s no better place than one in which lots of people are packed into small homes, living next to other families in small homes and rubbing up against each other every day. In fact, most major cities around the world have been shaped in one way or another by previous epidemics.

Humans are moving more. This includes people migrating across borders and flying around the world for business or pleasure. It’s no surprise that, in the United States, the city with the most international connections — New York — is always the first or hardest city to be hit by new infectious diseases, such as Zika, covid-19 and monkeypox.

Climate change has supercharged all of these factors. Extreme weather events, droughts and changes in temperature are leading humans to migrate to cities, cross borders and chop down forests and jungles to look for new land for growing crops or finding food. Those changes are not unique to humans. Animals, mosquitoes and ticks are also finding new places to settle, leading to “tropical” diseases now occurring in places no one ever thought of before as tropical.

So what can we do to stay safer? Make sure you and your family members are all up-to-date on vaccinations. You need to also make sure you stay as healthy as possible, including from chronic diseases such as diabetes and heart disease. Keeping good sleep habits, exercising regularly, eating a healthy diet, taking your medications as prescribed and seeing your doctor can keep you safer.

Stay aware of the news so you know what threats are on the horizon and take some time to think about what you would do if there is another respiratory virus pandemic or a massive contamination of the water supply: It turns out that thinking about these scenarios deeply for even a brief period can reduce anxiety and help you prepare if those events happen, like a fire drill.

You can also contact elected officials and ask them to support measures that strengthen public health and mitigate climate change. No matter how scary the world may seem right now, you do have the ability to do something about it.

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