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Why Are Infectious Diseases Emerging Faster Than Ever?

“The laws of biology haven’t changed, but the playing field has change dramatically.”

- William Karesh, DVM, Executive Vice President for Health and Policy, EcoHealth Alliance


“We’ve seen the difficulties we faced in this pandemic—we may face a more severe pandemic in the future and we need to be a hell of lot better prepared than we are now.”

- Dr. Michael Ryan, Irish epidemiologist, Executive Director, World Health Organization Health Emergencies Programme


In the book Microbial Threats to Health in the United States, Dr. Joshua Lederberg, an American molecular biologist and Nobel laureate, and his colleagues used the term “emerging infectious diseases” referring to “new infectious diseases appearing in the last 20 years, including those caused by newly identified species of pathogens or pathogens affecting a new population, as well as reemerging infections.” At the time of the book’s publication in 1992, emerging infections were occurring at an alarming rate. That rate is even more alarming now.

Since the beginning of the 21st century, we have witnessed the spread of chikungunya (2004) and Zika (2015) viruses, H1N1 swine flu pandemic (2009), a string of notorious coronaviruses—SARS (2003), MERS (2012), SARS-CoV-2 (2019), and now monkeypox. Why are these infections emerging faster than ever? In this Germ Gem’s post, I proffer an explanation.


Why do infections emerge? A large majority of infections categorized as “emerging” erupted because of three interacting factors: travel; zoonoses, that is spillover of pathogens from animals to humans; and disruptive changes in the environment.

The “sweet spot” of the diagram is “Human Behavior and Misbehavior.” That is, we humans play a central role in the development of emerging infections. Some of our behaviors, like travel or shipping things around the world, have fueled human progress. But sometimes, germs come along for the ride. From the perspective of the microbes, this an ingenious method to facilitate their spread around the world.


Microbes that “jump” from animals to humans, either directly, or indirectly via insect vectors (ticks and mosquitoes, in particular), are responsible for at least 60% of the estimated 140 emerging infections. As discussed in an October 6, 2021 Science article, “’Spillover’ diseases are emerging faster than ever before—thanks to humans,” zoonoses just keep on emerging. Because of this, over the past three years, I have devoted a number of Germ Gems posts to zoonoses.


Infections that spread across international borders are called pandemics. The two emerging infection pandemics that currently are capturing most of the global attention are: COVID-19, declared by the World Health Organization (WHO) a “Public Health Emergency of International Concern” (PHEIC) on January 30, 2020, and monkeypox which the WHO designated a PHEIC on July 16, 2022. (Both COVID-19 and monkeypox are zoonotic infections and have been subjects of previous Germ Gems posts.)


Changes in the environment, in particular alterations precipitated by climate change that resulted in destruction of the natural habitat of wild animals, is a third factor often underlying the emergence of infections.


Interconnectedness. In 1911, Scottish-American naturalist and ecologist John Muir wrote: “When we try to pick out anything by itself, we find it hitched to everything else in the Universe.” Emerging infections provide us with an excellent example of the interconnectedness of human, animal, and environmental health.


Yet, it took some time for those in the field of health care to recognize this interconnectedness. In fact, when I decided to pursue a career in the field of Infectious Diseases in the early 1970s, ecology, ecosystems biology, and climate change, were not even on my radar screen and were a void in medical training. Fortunately, this is no longer the case.

Future pandemics are inevitable. A new paradigm is needed to combat and prevent them. Talented scientists and professionals, from relevant disciplines (including human and veterinary medicine and public health), as well as from government organizations, like the Centers for Disease Control and Prevention (CDC), National Institutes of Health, and WHO, and businesses, including the pharmaceutical industry, will need to work together more creatively to ensure success in warding off the next pandemic.


There is some evidence that we are progressing on the right path. On July 20, 2022, the Biden administration announced that it is creating a new division within the Department of Health and Human Services to coordinate the nation’s response to pandemic threats. The new federal agency will be on a par with the CDC and the Food and Drug Administration. The creation of this new division which elevates the importance of a roughly 1,000-person team—known as the Office of the Assistant Secretary for Preparedness and Response (ASPR)—could mean that emerging infections finally get the attention and funding they deserve. I certainly hope so.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

 

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