Masks, Hand Sanitizer, Quarantines Protect Wild Chimps From Human Viruses, Too

TUCSON, Ariz. — The deadliest threat to wild chimpanzees could be the scientists trying to save them. A new international study shows that researchers were inadvertently spreading diseases to the apes they study, diseases that are minor annoyances to humans but can be fatal to our closest living relatives.

After 25 chimpanzees died from a respiratory virus that researchers unknowingly carried into Ugandan forests, the team took action. When researchers started wearing masks and using hand sanitizer around wild chimpanzees, the animals got sick 80% less often. Add a week-long quarantine, and illness dropped by 95%.

This research, published in Biological Conservation, took place in Uganda’s Kibale National Park. It shows us that basic health protocols can be powerful conservation tools, especially with how vulnerable endangered wildlife is to the diseases we carry, often without even feeling sick ourselves.

What Happened?

Between December 2016 and February 2017, researchers at the Ngogo Chimpanzee Project watched helplessly as a devastating respiratory outbreak swept through their study population. Twenty-five chimpanzees died in just two months. Scientists later identified the killer: human metapneumovirus, a virus that typically causes nothing more than cold symptoms in people.

Human-transmitted diseases rank among the top causes of sickness and death for wild chimpanzees. Unfortunately, the very people dedicating their lives to understanding and protecting these animals might be their biggest threat.

The researchers realized they needed to act fast. Starting in February 2017, they implemented strict health protocols that conservation groups had recommended for years but rarely tested scientifically. Researchers had to wear face masks around chimpanzees, sanitize their hands every 30 minutes, maintain greater distances from the animals, and follow strict clothing protocols.

When COVID-19 arrived in 2020, they added a mandatory seven-day quarantine for anyone entering the research site.

Counting Every Cough

Between 2015 and 2023, the team collected 45,167 health observations from 139 adult and adolescent chimpanzees. Every single day, team members noted whether each identified chimpanzee showed signs of respiratory illness, focusing primarily on persistent coughing.

Before the new protocols took effect, chimpanzees coughed in 1.73% of all health observations. After researchers started wearing masks and using hand sanitizer, that number plummeted to 0.356%. When the quarantine requirement was added, coughing occurred in just 0.075% of observations, a 95% reduction from the original baseline.

The team also analyzed 69 fecal samples to look for viral genetic material beyond what human observers could see. While they didn’t find clearly human-origin viruses in healthy chimpanzees, they discovered that the overall amount of viral genetic material in chimp feces decreased significantly after the health protocols began.

Why These Protocols Work

Wild chimpanzees share about 98% of our DNA, making them susceptible to many human diseases, but often with devastating consequences. Respiratory viruses that cause minor sniffles in humans can trigger fatal pneumonia in chimpanzees. With only around 300,000 chimpanzees left in the wild, every death matters for the species’ survival.

Researchers tracked the same population of chimpanzees across multiple years, creating what scientists call a “natural experiment.” They compared three distinct time periods: before additional health protocols (2015-early 2017), after basic measures like masking (2017-2019), and after quarantine was added (2022-2023).

The Ngogo site provided an ideal testing ground because it’s completely isolated from human settlements. The only people these chimpanzees encounter are researchers and park rangers, meaning the team could directly link changes in chimp health to changes in researcher behavior.

Invisible Spread

The study shows that humans can spread diseases to animals even when we feel perfectly healthy. Many of the protocols specifically targeted asymptomatic transmission, the same invisible spread that made COVID-19 so challenging to control in human populations. Combined approaches proved more effective against COVID-19 in humans than any single measure alone, suggesting the same principle likely applies to wildlife protection.

Research teams already follow strict protocols to minimize their impact on animal behavior, but disease transmission had received less scientific attention until recent deadly outbreaks exposed the risks.

“We have really good reasons to think that chimpanzees that are visited regularly by tourists are at even greater risk of this sort of transmission because they’re exposed to a wider range of people on a daily basis,” says lead author Jacob Negrey from the University of Arizona, in a statement. “The kind of trends we’re documenting here are really relevant to all of these human-chimpanzee interactions, not just ones related to research.”

Researchers work with endangered species worldwide, from mountain gorillas in Rwanda to orangutans in Borneo. Simple, relatively inexpensive measures can dramatically reduce disease transmission between humans and wildlife.

Working with wild chimpanzees isn’t for everyone. It isn’t the most glamorous experience, and you are met with a lot of the unexpected. Despite the challenges, Negrey and his team are passionate about their work.

“You can be wandering through the forest and then there’s rustling and you realize you’ve almost walked into a herd of elephants,” says Negrey, who is co-director of the Ngogo Chimpanzee Project, the nonprofit organization that runs the research site in western Uganda. “You have to really love the chimps and love the work that you’re doing because there’s a good chance you’re going to be peed on.

Twenty-five chimpanzee deaths exposed an invisible threat that likely exists wherever humans study wildlife. But those lives weren’t lost in vain if their story prevents future outbreaks and saves other endangered species from the diseases we carry without even knowing it.

“They’re so special, they’re so weird, and they’re really unlike anything else on the planet,” adds Negrey. “It’s to our great benefit to protect them for future generations so we can continue to be awed by them and continue to learn from them.”