Most modern epidemics have been caused by pathogens that spread from animals to humans. These zoonotic diseases have been predicted to increase with climate change.
Four types of animal-to-human infections are increasing at an “exponential rate” and could kill 12 times more people in 2050 than in 2020, according to a new study.
Researchers found a pattern of more frequent “spillover” epidemics after analysing nearly 60 years of epidemiological data.
The findings were published in the journal BMJ Global Health.
Most modern epidemics have been caused by pathogens that spread from animals to humans, also known as zoonotic diseases.
They can spread to humans via direct contact with animals, vectors such as ticks or mosquitoes, contact with an area where animals live, or consuming contaminated food or water.
The virus that causes COVID-19 is also known as zoonotic because it can transfer between animals and people. Scientists consider that transmission from animals to humans is the most likely explanation of the pandemic’s origins.
In the study published by researchers from the US biotech company Ginkgo Bioworks, they analysed historical trends in zoonotic spillover events from a wide range of sources.
Human-driven climate change has been expected to lead to an increase in zoonotic diseases, but its impact on global health is “difficult to characterise,” they explained.
Their new analysis determined that the number of spillover epidemics has been increasing by nearly 5 per cent annually, while the number of reported deaths has increased by 8.7 per cent annually.
“If the trend observed in this study continues, we would expect these pathogens to cause four times the number of spillover events and 12 times the number of deaths in 2050, compared with 2020,” the researchers said.
Estimates are ‘likely conservative’
They studied a database of more than 3,000 outbreaks and epidemics and focused on the period between 1963 and 2019.
They analysed four types of zoonotic pathogens: Filoviruses (such as Ebola and Marburg), SARS Coronavirus 1 (which causes SARS), Nipah virus (associated with swelling of the brain), and Machupo virus (which causes Bolivian haemorrhagic fever).
The researchers identified 75 spillover events in 24 countries which caused more than 17,000 deaths, with most of the deaths caused by filoviruses in Africa.
Their estimates are likely “conservative,” the researchers said, due to the specific inclusion criteria for the pathogens and the omission of the COVID-19 pandemic which is “several orders of magnitude larger than other events”.
“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.
They said that if this trend continues it would cause a large increase in global infectious disease risk.
While many surveillance programmes and pandemic risk proposals have been made, the researchers say that the “ultimate package of measures” to support pandemic preparedness is not clear.
“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 study authors added.