What does 11 Billion People Mean for Disease Outbreaks?

The latest population projections from the United Nations, announced in a new report last summer, estimate that the world’s population will reach 9.6 billion people by mid-century, and 11 billion by 2100.

The sheer number of people, their interactions with animals and ecosystems, and the increase in international trade and travel are all factors that will likely change the way humanity deals with preventing and treating epidemics, experts say. In fact, the unprecedented growth of the human population in the second half of the last century — growing from 2.5 billion to 6 billion — may have already started changing how infectious diseases emerge.

“There’s a strong correlation between the risk of pandemic and human population density. We’ve done the math and we’ve proved it,” said Dr. Peter Daszak, a disease ecologist and the president of Eco Health Alliance, who examined the link in a 2008 study published in the journal Nature.

Looking at contemporary outbreaks since the mid-20th century, Daszak and colleagues found that the rate of emergent diseases caused by pathogens new to humans has increased significantly with time, even when controlling for progress in diagnosis techniques and surveillance, which could make it only seem like diseases were on the rise. More than 300 new infectious diseases emerged between 1940 and 2004, the study found.

Some of these diseases were caused by pathogens that have hopped across species and finally into humans — for example, the West Nile virus, the SARS coronavirus and HIV. Others were caused by a new variant of a pathogen that evolved to thwart available drugs, such as drug-resistant tuberculosis and malaria.

Certain pathogens, such as the bacteria that cause Lyme disease, are not new to humans, but their incidence increased dramatically, perhaps due to changes that newly arrived humans made to the environment inhabited by animals carrying these pathogens.

In light of the continuous population growth, health authorities are calling for strengthening public health organizations, and giving more resources to systems that would protect people. Researchers are studying ways to identify viruses faster, so that vaccines could be developed early in the process, and scientists are trying to understand the complicated interactions between humans and the surrounding ecosystem, so that they could identify emerging disease hotspots and find the next emerging virus before it finds humans. All of these are done in an effort to have the new creative solutions that preventing pandemics on a populated planet would require.

“You can predict very confidently as each year moves forward, we’re going to see more and more diseases emerge,” Daszak said. “It’s a little abstract to most people. And to be fair, it’s new for scientists too.”

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