“The sense that a pandemic is impending is really growing,” Sonia Shah said on Wednesday morning, kicking off IdeaFestival 2016 in Louisville, Kentucky.

Shah, an investigative journalist and the author of Pandemic, explored the root causes of the spread of disease, tracing the origins back hundreds of years.

The question is: Which pathogen will cause the destruction? A million kinds of viruses can infect mammals, said Shah, so determining which one it could be is “a lost cause.” Still, she said, there are very few pathogens that cause a pandemic.

Vibrio cholerae, or cholera, is the one that interests Shah most. It’s highly deadly, killing half of the people it infects. And it’s one of the most “successful pandemic-causing pathogens,” with a record of causing seven pandemics.

Shah explored the circumstances around the rise of cholera, which hit New York in 1832. While we often think of pandemics affecting the poor, back then, it struck cities like London, Paris, New Orleans, and New York.

“It was not just deadly,” Shah said, “it was disruptive.”

How a microbes emerge and diseases spread

It begins in the environment, Shah said. In a marine environment, such as coastal estuaries, bacteria in the water helps recycle nutrients. The problem arises, however, when humans begin to intervene.

“For most of human history,” said Shah, “humans had nothing to do with cholera.” That’s because people didn’t want to live in areas near crocodiles and other dangerous wildlife. But when the British colonized the land in Southeast Asia where rivers were flowing, turning the land into rice farms, people suddenly came into contact with bacteria-rich water. The bacteria then took on a new function–in humans, it began extracting fluids, and expelling them from the body. “A person with cholera can lose 15 liters of fluid,” said Shah. “That’s what kills you.”

Cholera can spread easily, simply by sharing the same water. And when new modes of transportation, like ships, came onto the scene, the disease could cross the Atlantic, and could quickly penetrate a continent, Shah said.

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In the 19th century, rapid urbanization, and the rise of factory jobs, were major factors in the spread of disease. Without buses and trains, people needed to live close to where they worked. In the most crowded parts of New York City, for example, there were 77,000 people per square mile–that’s 1000 times more crowded than anywhere had been in history, and six times more crowded than modern-day Tokyo. This created a sanitary crisis, said Shah. There was no plumbing system, and waste spilled into the streets.

A typical New Yorker at the time ingested two teaspoons of fecal matter a day from the water supply.

Private interests

So why was it so hard to stem the spread of cholera? It was a time of robber barons and big business, Shah said. The disease was clearly coming down the Hudson and Eerie River to the city. So why did the government fail to quarantine the rivers?

Companies were making money selling cholera-contaminated water. A group of people wanted to save money, so they collected water that was nearby to transport to New Yorkers. They wanted the money to start up a bank. The bank they founded is now the largest in the country: JPMorgan Chase.

So: Could something like this happen again?

Yes, Shah said. In fact, the potential for the spread of pandemics is growing. “A lot of drivers that allowed cholera to become a pandemic are here today,” she said, “on a global scale.”

We are invading wild habitats,” said Shah, “on a scale never seen before.” The new interactions with the animals, she said, means that microbes in their bodies can spill into our bodies. In fact, 60% of pathogens today come from animals.

A big factor in this is deforestation. In Africa, in Guinea, Sierra Leone, and Liberia, the steady chopping down of trees has led to the destruction of one of the most bio-diverse forests in the world.

It’s where fruit bats live. So now, Shah said, they roost in farms and gardens and backyards, where their microbes can spread.

Remember Ebola? It came from a fruit bat. In 2013, a two year old boy was playing near a tree. He picked up an infected fruit, which set off a chain of infections–to parents, then health care workers, then other families. That led to the biggest outbreak in history. Eleven-thousand people died.

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We’re driving pathogens into human populations, said Shah. And at our current rate of urbanization, more than half of the world’s population will live in cities by 2030–2 billion of them in slums.

Another major factor is the over-crowding of animal populations. There are more domesticated animals today than in 10,000 years of domestication–combined. This leads to the “animal equivalent of a slum,” said Shah, “a factory farm.” These conditions then lead to increased contact, and a faster spread of diseases, like H5N1, that can then infect humans.

The crowding also leads to a sanitary crisis, Shah said. Currently, there are 2.6 billion people without access to modern sanitation. Much of this is because of livestock waste–there’s 7 billion tons of excreta across the globe right now, she said. These manure lagoons, open cesspools, mean that any time it rains, pathogens can spread.

What we can do

Misunderstanding where pandemics come from often lead us to misplace blame. “In a vacuum of understanding,” Shah said, “people blame others.” Cholera, for example, was first pinned on Irish immigrants; then Muslims; then Eastern Europeans.

But it’s not just “verbal scapegoating,” Shah said, “It became violent.” Mass graves have been discovered, Shah said, around sites of outbreaks.

Today, we need to overcome xenophobia and scapegoating, she said. We are over-fixating on outbreaks, treating them as biomedical problems and targeting them with pinpoint accuracy, and “military might,” but ignoring the socio-political factors involved.

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Public health has been trying to address issues that could stem the spread of disease, such as the overuse of antibiotics for commercial purposes. But lobbyists often block these causes, such as farming groups who profit from the sales of cattle, fattened up with antibiotics.

“We know the biomedical approach has failed,” Shah said.

Early detection, she said, is key. “Since we know how it happens, we can figure out where it happens.” And modern tools allow us to use data to map hotspots of disease, which we can use to actively look for microbes before they turn into pathogens.

We should be sampling miners, farm workers, wild animals, and livestock, she said. Now, it happens in an ad hoc way with NGOs and some government agencies taking on the job.

We must “reimagine our relationship to the microbial world,” said Shah.

The health of people is connected to health of animals, and the health of ecosystems. It will require political will, she said.

“We will never get rid of infectious diseases,” said Shah, “but we can prevent pandemics.”

And, data will be one of the key enablers.