Skip to main content

Experts Discuss Ways to Prevent Animal to Human Disease Outbreaks

A group of pigs stand grouped tightly together. Pig livestock are a major carrier for several zoonotic diseases.
Livestock can be significant carriers of zoonotic diseases.
Photo credit: ArtbyPixel/Shutterstock

Understanding disease spread from humans to animals could help mitigate the emergence, re-emergence and spread of these zoonotic diseases, said Andrew Peter Dobson, Xiang-Jin Meng and James A. Roth in a recent discussion on preventing future pandemics.  

The three scientists spoke during the 2021 Charles Valentine Riley Memorial Lecture on Sept. 30, addressing their work on zoonotic diseases and the role of agricultural research in preventing future pandemics. All three speakers emphasized the importance of prevention when looking to the future of zoonotic disease, offering insight on where to focus future research efforts and political action.

The talk comes during the second year of a global pandemic likely linked to zoonotic disease spread. The Centers for Disease Control and Prevention estimate that six out of every 10 known infectious diseases in people can be spread from animals. Three out of every four new emerging infectious diseases in people come from animals. “I can think of no challenge for which the benefits of science and innovation are more urgently needed,” AAAS CEO Sudip Parikh noted in his opening remarks.

The annual Charles Valentine Riley Memorial Lecture is a collaboration between AAAS, the Charles Valentine Riley Memorial Foundation and the World Food Prize Foundation held since 2008.

Calculating Costs

During his presentation, Dobson, professor of ecology and evolutionary biology at Princeton University, illustrated the increase in zoonotic outbreaks throughout recent history, mapping the global scale of pandemics over the course of the last 100 years. “To a good approximation, we get two new viruses every year trying to establish in human populations,” said Dobson. As the global human population increases, though, “more and more of these pathogens are able to establish and take off.” Through time, there are fewer years without a major epidemic outbreak, and the size of outbreaks are increasing due to population size.

Dobson also tracked an increase in the economic cost of each outbreak and encouraged a model that focuses on saving costs through rigorous prevention efforts instead of retroactive disaster relief. The total cost of the COVID-19 pandemic lays somewhere between $13 and $14 trillion dollars, Dobson reported in a paper currently under review, while the estimated cost of preventing a pandemic for another 10 years is $260 billion. The cost of preventing the next pandemic, concluded Dobson, is just 2% of the COVID-19 bill.

Emerging diseases are also threatening livestock species and food security, Roth said in his presentation. Roth is a Distinguished Professor in the College of Veterinary Medicine at Iowa State University. He noted that, along with an increase in human population, there has been a major expansion in food animal populations, allowing “more and more opportunity for infectious agents to evolve and mutate and spread.”

He cited several case studies, including highly pathogenic avian influenza and African swine fever, both of which have threatened food security across entire countries. Other diseases, like Nipah virus in swine, spread easily between animals with occasional transmission to humans. Roth noted that prevention is equally as important in these examples, and that the emphasis should lay on controlling animal to animal transmission.

Addressing Root Causes

To prevent the emergence and spread of zoonotic disease, all three scientists agreed on the importance of tackling root causes of spread. They cited environmental changes like deforestation and climate change as major mechanisms behind the interspecies transfer of pathogens. Increased intensification of global agricultural practices was also raised several times by the speakers, who emphasized that disease spillover from livestock plays a major role in zoonotic emergence and spread.

As part of his economic analysis, Dobson proposed a series of investments needed to successfully prevent future zoonotic disease outbreaks. He noted the importance of limiting tropical deforestation, reducing pathogen spread from livestock and monitoring global wildlife trade. These areas, said Dobson, are not currently receiving enough funding to help prevent a future pandemic.

Dobson also called veterinarians and wildlife disease biologists the “first line of defense” in zoonotic disease outbreaks. While the U.S. has an average relative abundance of veterinary staff, Dobson said, many African countries as well as parts of South Asia and South America are “woefully and inadequately” lacking these “front line defenders.” He suggested a significant global increase in veterinary staff and wildlife disease biologists to identify zoonotic diseases before they spread to the human population.

Meng, a University Distinguished Professor at Virginia Tech, shared similar prevention points, emphasizing the importance of a One Health approach that encourages an interdisciplinary perspective. One Health, said Meng, refers to the concept that humans, animals and the environment are inseparably linked together. “In order to have healthy humans, we must also have healthy animals and a healthy environment.”

Meng said that deforestation, wildlife wet markets, intensive farming practice and climate change all bring animal pathogens closer to human habitat, leading to spillover and cross-species infection. These places are the interfaces of human, animal and environmental contact, places where prevention is most important.

Dobson, Meng and Roth all agreed that the COVID-19 pandemic provided an example of how zoonotic diseases may become larger outbreaks in the future, emphasizing the need for more rigorous preventative practices. Meng said, “The COVID-19 pandemic really provides a sobering reminder that we will have to take a long and deep look at the root cause of all this emerging infection and invest the resources to address them.”