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Can we successfully predict the next pandemic?

American Centers for Disease Control and Prevention (CDC) estimates that more than 60% of known infectious human diseases originate in animals.

Medical terminology like “lipid envelope” and “coronavirus” might have just become household terms for most of the world, but for scientists like Kevin Olival, viruses are a more normal part of the workday than an 8 AM coffee. In a typical workweek, Dr. Olival might spend a couple weeks in a country that is a potential virus hotspot, taking samples from animals, which will later be analyzed in a lab. Dr. Olival is partnering with an organization called USAID PREDICT, a nonprofit dedicated to tracking potential sources of zoonotic illness and preventing pandemic outbreaks.

Zoonotic illnesses are diseases spread from animals to humans. Animal-borne diseases have been behind some of the world’s worst pandemics, from the bubonic plague, which originated in rats, to the Spanish influenza, which originated in birds. A zoonotic illness is even the source of COVID-19, the novel coronavirus which has spread from Wuhan, China into over 150 countries. Ultimately, the American Centers for Disease Control and Prevention (CDC) estimates that more than 60% of known infectious human diseases originate in animals.

By tracking potential sources of zoonotic illness, organizations like PREDICT are hoping to keep disease from jumping from animals to humans. Virus hunters have a variety of methods for identifying animal diseases which might someday infect human populations. Some researchers have used a database of emerging infectious diseases to map the global hotspots where pandemic outbreaks are likely to originate. The PREDICT project utilizes this method, identifying central Africa, South and Southeast Asia, and Latin America as “hotspots” for zoonotic illness. Similarly, the Cary Institute’s Dr. Han collected data regarding the geographic distribution of disease-carrying mammals and named South Africa, Eastern Africa, certain parts of Europe, and the subarctic as potential virus hotspots.

After identifying these “hotspots,” researchers can begin investigating species which have the potential to harbor zoonoses. Dr. Han’s research led her to wonder whether artic carnivores, species which already harbor that carried higher numbers of disease than expected. Other organizations are tracking more concrete results. Since the PREDICT project began taking samples from various species to help identify areas where viruses are likely to emerge, the organization has identified over 1,000 new viruses in 20 different countries.

However, whether scientists can actually predict pandemic outbreaks remains the subject of intense scientific debate. According to Dr. Robert B. Tesh, a virologist at the University of Texas Medical Branch, science doesn’t yet have enough of a handle on zoonotic illnesses to make effective predictive models. Even the Cary Institute’s Dr. Han notes that the data that would allow her and her colleagues to predict the next zoonotic illness is especially lacking, and that when it came to animal-borne illness, “there was no baseline of where these things lived [or] which species carried what.”

Further, even after researchers successfully identify zoonotic illness, myriad of other complications remain. Dr. Tesh argues that certain viruses, like Zika or West Nile weren’t “new” when they led to infectious outbreaks; rather, they were unpredictably transported to new areas before infecting thousands. Viruses can also mutate quickly and unpredictably, dying out or infecting new hosts in a manner that “no amount of discovery can prepare for.” Even after a virus is identified in animals, there is not guarantee that the particular illness will infect humans. This fact has led evolutionary biologist Dr. Stephen Holmes to argue that there are not enough generalities to predict which illnesses will leap into humans, making the mere idea of predicting pandemic illness “foolish.”

And this doesn’t even cover the known zoonoses for which we still cannot accurately identify an animal host. Six years after the West African Ebola outbreak, which claimed over 11,000 lives, researchers still cannot definitely claim bats as the source of the infection. Researchers have thought that the two-year old patient zero had contracted the illness from playing with bats but couldn’t be certain.

The whereabouts of the animal which has caused the current coronavirus pandemic are similarly ambiguous. Some researchers at the South China Agricultural University in Guangzhou used genetic analysis to trace the coronavirus to a similar illness found in smuggled pangolins that was a 99% genetic match to the virus that has infected thousands of people. Other researchers suggest that bats, operating through an intermediate species, were the ultimate source of the disease. If Ebola is any lesson, we might be debating the question—as well as other questions related to the prediction of pandemic illnesses—for years to come.

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