Pathogens once contained in isolated animal populations have sparked deadly epidemics at an exponential rate over the past half a century, according to a new study, setting a trend that is likely to only worsen in coming years.

According to an analysis of historical data by biotech company Ginkgo Bioworks, outbreaks reported from a selection of four devastating viruses with animal hosts rose by nearly 5 percent a year between 1963 and 2019, with deaths jumping annually by an astonishing 8.7 percent.

At that rate, the researchers predict, we could expect the total number of fatalities from these four diseases alone to be at least 12 times greater in 2050 than records showed for 2020.

Most modern viral epidemics have their origins in populations of wild or domestic animals that harbor pathogens with little to no ill effect themselves, passing them on silently from generation to generation.

Should the virus evolve a talent for breaking into a human body, any chance meeting between us and the animal host presents an opportunity for a zoonotic spillover event – an invasion of pathogenic pioneers wreaking havoc as they launch themselves into our population.

Human activity has dramatically increased the likelihood of those initial encounters, such as by pushing deeper into wild habitats or by forcing relocation of populations through widespread habitat loss and climate change. While this much is understood, little is known about the actual frequency of zoonotic spillovers over time, making long-term assessments a challenge.

With access to an extensive database on infectious disease outbreaks, Ginkgo Bioworks was in a prime position to examine the number and severity of zoonotic outbreaks reported by the World Health Organization in recent history.

Excluding the recent COVID-19 pandemic (on account of its blinding devastation) as well as potentially endemic diseases that may have established themselves in human populations, the researchers settled on a handful of animal-borne viruses; – SARS coronavirus 1, filoviruses such as Ebola, Machupo virus (which causes Bolivian hemorrhagic fever), and Nipah virus.

The researchers were left with 75 events that spilled over into human populations from wild hosts in 24 countries. Tracking their emergence and using death count as a guide to each outbreak's severity, filoviruses were by far the deadliest, with more than 15,700 deaths in the 40 outbreaks reported over the period studied.

By comparison, SARS-CoV-1 claimed just 922 lives, though this was amid just two outbreaks between 2002 and 2004. Machupo and Nipah viruses together accounted for 529 deaths in 33 outbreaks.

Though the events appear to be fragmented and spread across the decades, the researchers say the epidemics aren't the result of random activities, carrying signs of a trend that appears to be rising.

"If the trend we observe in this study continues, we would expect to see these pathogens cause four times the number of spillover events and 12 times the number of deaths in 2050, compared with 2020," the team writes in their report.

This figure doesn't even take into account monolithic examples like COVID-19, putting such estimates on the conservative side.

If a deadly pandemic has shown us anything, it's that governments are capable of funding surveillance and monitoring programs when met with a rising death count.

Knowing those statistics could be set to rise for a whole swathe of epidemics in the future, it might be time to expand infrastructure and technology to keep a better watch on the wild frontiers of animal viruses.

This research was published in BMJ Global Health.