Anyone who has been on the planet for the last four years will know how viruses that evolve to jump across species, given the right conditions, can rapidly become a serious global crisis. While COVID-19 was a rare ‘perfect storm’ for a zoonotic virus to get out of control, international researchers believe we’re now in an alarming new age of vertebrate animal-to-human infections.
A comprehensive study of epidemiological data dating back 60 years has turned up a worrying trend in zoonotic infections in humans, with prevalence and morbidity increasing at an “exponential rate,” according to the researchers.
“Emerging zoonotic viruses that subsequently spread from human to human are the focus of this analysis because they were the cause of most 20th century pandemics, and account for 60% of all emerging human diseases,” the researchers from US biotechnology organization Gingko Bioworks noted.
Drawing on a range of datasets, the researchers analyzed 3,150 zoonotic outbreaks and epidemics between 1963 and 2019, looking for trends in infections and mortality. They were particularly interested in the viruses that had the COVID-19-style ‘perfect storm’ potential for exponential spread – the ones posing the biggest risk to public health, economic and political stability.
They zeroed in on 75 spillover events in 24 countries, which resulted in 17,232 human deaths. Incidentally, 15,771 of those deaths, in 40 outbreaks, were caused by Filoviruses. Filoviruses, which include Ebola and Marbug, were among the four ‘bad news’ pathogens identified. The other three of interest were SARS Coronavirus 1, Nipah virus and Machupo virus.
“If these annual rates of increase continue, we would expect the analyzed pathogens to cause four times the number of spillover events and 12 times the number of deaths in 2050 than in 2020,” they estimated.
While COVID-19 is a zoonotic outlier and as such was excluded from the data, the number of spillover events and reported deaths from the four groups of viruses has increased by 4.98% and 8.7%, respectively, every year from 1963 to 2019.
“Our evaluation of the historical evidence suggests that the series of recent epidemics sparked by zoonotic spillover are not an aberration or random cluster, but follow a multi-decade trend in which spillover-driven epidemics have become both larger and more frequent,” they wrote.
Nipah virus (NiV), which has a reservoir in fruit bats or flying foxes, results in encephalitis and can cause everything from mild illness to death. Similarly, flying foxes are thought to be the natural reservoir for Ebolaviruses.
The Severe Acute Respirator Syndrome (SARS) coronavirus is also thought to have crossed over into human populations from bats.
Machupo virus, a highly infectious hemorrhaging infection, is considered the Bolivian cousin of Ebolaviruses and jumped to humans in the 1950s due to increased interaction with the Calomys field rodent.
But while zoonotic virus outbreaks have been isolated and largely contained in the past, with a few very obvious exceptions, their increased frequency and severity now has scientists very concerned.
Adding to the worry is lax and fragmented historical data detailing viral outbreaks, which makes modeling for future epidemics or, worse, pandemics, difficult.
“The ultimate package of measures to support global prevention, preparedness, and resilience is not yet clear,” they note. “What is clear, however, from the historical trends, is that urgent action is needed to address a large and growing risk to global health.”
This comes as scientists are learning more about the extent and evolution of mpox, or MPXV (formerly monkeypox, since it likely spread from rodents, not monkeys), and as avian influenza H5N1 threatens to swap favored host from bird to mammal.
Zoonotic pathogens can be bacterial, viral or parasitic, and can spread to humans through direct contact or via food, water or the environment. According to the World Health Organization, there are now more than 200 known zoonoses, or diseases that can be transmitted to humans from animals.
“What is clear, however, from the historical trends, is that urgent action is needed to address a large and growing risk to global health,” the researchers said.
The study was published in the journal BMJ Global Health.
Source: Ginkgo Bioworks