‘Spillover events’ from zoonotic diseases threaten surge in deaths, research warns

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Five animal-to-human diseases threaten to cause the deaths of 12 times as many people in 2050 as in 2020, according to research that calls for “urgent action” to tackle the growing health threat posed by zoonotic infections. 

Concerns over zoonotic diseases have greatly increased since the Sars-Cov-2 coronavirus emerged in China in late 2019 and spread swiftly across the globe. A study published by BMJ Global Health on Thursday found that environmental and population changes over the past six decades were driving growing numbers of such “spillover events” such as that which caused the coronavirus pandemic.

“It’s not just that we are seeing more of these events but they are persisting longer and generating more fatalities,” said Ben Oppenheim, co-author of the BMJ paper and senior director of US company Concentric by Ginkgo, which works with governments on early warning monitoring of pandemics. “It points not just to the risk, but to the magnitude of the work needed to mitigate it.” 

Efforts have already been stepped up to detect disease outbreaks in areas of high population density, but the researchers recommended other measures such as increased assessment of pandemic risks driven by climate change and deforestation.

A separate study published by Science on Thursday found the mpox virus that triggered an international health emergency last year has been transmitted between people for much longer than thought.

The Concentric researchers focused on a group of “high consequence” pathogens: the Ebola and Marburg filoviruses that cause haemorrhagic fevers, Nipah, Machupo and Sars-CoV-1 — a genetic forebear of Sars-CoV-2. They used a database of more than 3,150 outbreaks and epidemics from 1963 to 2019.

The viruses caused a total of 17,232 recorded deaths in 75 spillover events across 24 countries in Africa, Asia and South America. Outbreak and death numbers increased at an “exponential rate” over the 56-year period of the analysis up to 2019, the researchers found. 

If those trends continued, then spillover events from the group would be four times higher and deaths 12 times higher in 2050 than in 2020, they concluded — a forecast they characterised as “conservative”. The rise reflects how environmental changes and growing population density are increasing inter-species contact and human-to-human infections.

The separate new research on mpox, the disease formerly known as monkeypox, found mutations that suggest it has been circulating in humans and interacting with their immune systems since 2016. This contradicts assumptions previous to the 2022 emergency that mpox cases were mostly independent spillover events from rodents to humans, with only limited cross-infections between people.

Efforts to monitor and suppress mpox, which was first identified in captive monkeys, will need to be stepped up to control its spread, the international team of researchers concluded. “Surveillance needs to be global if [the virus] is to be eliminated from the human population and then prevented from re-emerging,” they wrote. 

The World Health Organization, which stopped classifying mpox as a global health emergency in May, has proposed a global accord on pandemic preparedness and is working with other agencies on early warning, prevention and control of zoonotic disease threats.

The research suggested more attention should be paid to preventing pandemics than responding to them, said Professor James Wood, an infectious diseases expert at the Cambridge university.

“Our global human impacts [such as] how we grow our food and exploit natural resources . . . are progressively increasing the risk of future Covid-19-type pandemics,” he said. “Such considerations are politically and economically complex, but we are ignoring them at our peril.”