Even as the COVID-19 pandemic rages on, experts are warning that the next pandemic could arrive at any moment, and again, it could come from animals. To prevent history from repeating itself, experts say governments need to start investing heavily in pandemic prevention efforts.
That means deploying teams of biologists, zoologists and veterinarians to begin monitoring animals and the people who interact with them -- an army of scientists tasked with stamping out the next deadly virus before an animal disease balloons into a global pandemic.
According to the World Health Organization, approximately 1 billion cases and millions of deaths each year can be traced back to diseases originating from animal populations.
In the past three decades, researchers have found more than 30 bacteria or viruses that are capable of infecting humans. Over three quarters of those are believed to have come from animal populations.
And while the current pandemic may feel like a very rare happening, scientists say the pace of these pandemics is accelerating dramatically thanks to humans' ever-encroaching proximity to wildlife.
Beginning with SARS almost two decades ago and followed by West Nile, Ebola, Zika and currently, COVID-19, many of these pandemics originated with species of bats, and can be spread between people through coughing and sneezing or through insects such as mosquitoes.
"The time between these outbreaks is getting shorter and shorter," said Dr. Tracey McNamara, a professor of pathology at Western University of Health Sciences College of Veterinary Medicine.
And it's becoming increasingly clear that these viruses aren't just a threat to our health -- they're also a threat to the global economy.
"We are only able to sustain an outbreak maybe once every decade," said Dr. Peter Daszak, president of EcoHealth Alliance. "The rate we are going is not sustainable."
The COVID-19 pandemic did not surprise McNamara and Daszak. For decades, they, and other scientists, have been warning politicians and the public that wild and domestic animals -- and the viruses they carry -- pose a threat to humanity.
Without proper monitoring and surveillance of these creatures, they warned, we would be ill-prepared to stop a virus from spreading across the globe. McNamara was part of the "Red Dawn" group, a now-infamous email chain of top scientists that asked powerful U.S. government officials to mount a more vigorous domestic defense back when coronavirus was still considered a problem confined to China's borders.
And Daszak, who has spent much of his career hunting for the next pandemic-causing virus in bat caves in Asia, saw U.S. government funding for his science slashed back in April.
Perhaps most ominously, a U.S.-funded early-warning system called PREDICT, which was launched in 2009 in response to the H5N1 bird flu outbreak, saw its funding quietly lapse in late 2019. Daszak, whose group EcoHealth Alliance received some funding from PREDICT, lamented its loss at the time, arguing it's much cheaper for governments to stamp out small outbreaks than try to control a massive pandemic.
But there are some signs now, with the coronavirus pandemic in full swing, that funding to these crucial programs is coming back. PREDICT was granted an emergency six-month extension, and a new program, called Stop Spillover, is slated to launch in October.
And while it may be too late to stop this coronavirus in its tracks, scientists say the threat of the spillover event grows more imminent each year. As our population continues to expand, the interactions between humans and wildlife grow closer and closer. Cutting down forests and altering habitats push animals out of their own homes and deeper into human communities.
Poorly developed hygiene and sanitation systems can make it more likely for germs to build up. With humans and animals living in such close proximity, bacteria and viruses can easily jump from one species to another.
Once people become infected, the increasing interconnectedness of our world makes the spread of the disease easier. People and domestic animals are able to traverse the globe in a matter of hours. Illegal trade of exotic animals can move across borders undetected, carrying with them deadly bacteria and viruses.
"Several epidemiological drivers have been identified that make bacteria and viruses from animal populations suitable to emerge in a susceptible population. These drivers include climate change, industrial development, ecosystem change and social inequality," said Dr. John Brownstein, an epidemiologist, chief innovation officer at Boston Children's Hospital and contributor to ABC News.
So how do bacteria or viruses go from infecting animals to infecting humans?
One of the most common ways is coming into direct contact with the bodily fluids of an infected animal, such as a bat. This includes saliva, blood, urine and feces. Indirectly, people can come into contact with these through soil, plants, in animal habitats or by eating or drinking something that is contaminated.
Mosquitoes and ticks are two animals that are known to easily spread bacteria and viruses, including West Nile and Zika virus. After biting an infected person, mosquitoes and ticks are able to spread the virus to every subsequent person they bite.
According to McNamara, rabies and plant diseases that can damage crops are the two diseases under surveillance in the United States.
"We don't think about it in the United States as much," said Dr. Christine Johnson, a professor of epidemiology and ecosystem health at the University of California--Davis School of Veterinary Medicine and director of the EpiCenter for Disease Dynamics. "There is a lot of active work to maintain vigilance for diseases. There is currently an outbreak of Ebola going on right now in the Democratic Republic of the Congo."
In Southeast Asia, efforts at identifying emerging diseases are focused on testing for viruses in both animals and people, especially in places where viruses can spill over, or find a new host, such as in humans, explained Daszak.
"We only know how to look for known diseases," said McNamara. Her vision is for a disease surveillance system to focus syndromes, a group of symptoms that are known to occur together.
By empowering veterinarians to share their findings with each other, McNamara hopes that this can help experts quickly identify the source of an outbreak before it spreads.
"Future efforts in zoonotic disease surveillance should include strong integration of animal and human agencies of health, including wildlife, agriculture and public health," added Brownstein.
Jonathan Chan, M.D., is an emergency medicine resident at St. John's Riverside Hospital and a contributor to the ABC News Medical Unit. Sony Salzman is the unit's coordinating producer.