Deaths from a handful of viruses that spill over from animals to humans are set to increase 12-fold by 2050 due to climate change and habitat encroachment, according to a new study published in the British Medical Journal.
Three of the four—filoviruses like Ebola and Marburg, SARS, and Nipah virus—are on the World Health Organization’s list of priority pathogens, noted for their potential to cause the next pandemic.
But the Ebola-like Machupo virus is also a contender, the authors of the new study argue. And regardless of which pathogen ends up fueling the next global health crisis, they’re all worthy of attention, the authors maintain.
The reason: Epidemics of the viruses they focused on are set to cause a combined death toll of more than 15,000 annually by 2050, even if they don’t make an evolutionary leap that allows them to ravage the globe.
Researchers at Boston-based biotech firm Ginkgo Bioworks honed in on four viruses likely to pose a significant public health risk and endanger economic or political stability. Called zoonotic viruses, they spill over from animals to humans, who can then transmit them to other humans.
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Filoviruses like Ebola and Marburg
Viruses in this family cause hemorrhagic, or bloody, fevers, which are typically accompanied by bleeding from bodily orifices and/or internal organs. The family consists of five strains of Ebola in addition to Marburg—an extremely similar virus that made headlines during an outbreak in Equatorial Guinea earlier this year.
On average, Ebola kills about 50% of those it sickens, though case fatality rates have ranged from 25%-90%, according to the WHO. Marburg also kills around 50% of those it infects, though case fatality rates range from around 24% to 88%, experts say. While there are two licensed vaccines for the deadliest strain of Ebola, Zaire, there aren’t any for the four other strains. Nor is there an approved vaccine for Marburg, though some are in development.
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The original SARS
The world’s first confirmed coronavirus pandemic occurred in 2002, when SARS-CoV-1 was reported in China. It spread to more than two dozen countries in North and South America and Europe before being contained seven months later. It is thought to have originated in an animal population, perhaps bats, before being passed to civet cats—a tropical animal that looks like a mix of a dog and an ocelot—then to people. A spill-over could happen again.
Symptoms include headache, body aches, mild respiratory symptoms, possible diarrhea, an eventual dry cough, and pneumonia in most. SARS sickened nearly 8,100 people and killed just under 10% of them from 2002 to 2003. There is no licensed vaccine for SARS, though researchers are working on universal coronavirus vaccines that could target both SARS and COVID, among other coronaviruses.
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Nipah is a henipavirus, the most lethal of paramyxoviruses. It was first identified in pigs in Malaysia and Singapore in the late 1980s, though its natural reservoir is fruit bats. The other henipavirus known to infect people, Hendra, was first noted in racehorses and humans in Australia in 1994. Both feature respiratory illness and severe flu-like symptoms, and may progress to encephalitis—inflammation of the brain—along with other neurologic symptoms and death.
Nipah kills between 45% and 75% of the people it infects. No licensed vaccines exist, though a vaccine by Moderna, in coordination with the U.S. National Institute of Allergy and Infectious Diseases Vaccine Research Center, is being evaluated.
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Also known as “black typhus” and Bolivian hemorrhagic fever, Machupo was first isolated in Bolivia in 1959. The Calomys callosus field mouse is a natural carrier of the virus, the symptoms of which are Ebola-like and include bleeding, high fever, pain, and rapid death.
Machupo kills between a quarter and a third of those it infects. Though there are no licensed vaccines for it, a vaccine for Argentinean hemorrhagic fever—caused by the similar Junin virus—may also offer protection against Machupo, according to Stanford University.
Researchers only looked at outbreaks that killed 50 or more people between 1963 and 2019. They didn’t take into account the following viruses, which may have otherwise met their criteria:
• SARS-CoV-2: The virus behind the recent COVID pandemic may have been caused by a lab leak instead of spill-over from an animal like a raccoon dog or pangolin. Thus, it’s not certain that the virus is zoonotic. What’s more, including this disease could skew the study’s numbers, making projected deaths look higher than they potentially should be. Regardless, the COVID pandemic occurred just after the study’s 2019 cut-off. COVID is, however, on the WHO’s list of priority pathogens.
• Hantaviruses and Lassa virus: Both rodent-spread viruses were eliminated from consideration because surveillance has increased over time, potentially causing the growth of studied viruses to appear greater than it should be.
• Flu and vector-borne pathogens: Flu viruses like 2009’s H1N1 and vector-borne diseases like Crimean-Congo haemorrhagic fever and Zika virus were excluded—the former due to surveillance programs that have grown with time, with the potential to skew predictions on the high end, and the later due to eradication programs that have the potential to skew predictions on the low end.
Bloody fevers lead outbreaks, deaths
When crunching numbers on outbreaks, researchers looked at the number of dead, not the number infected. That’s because the number of fatalities is typically more accurate, given that people can contract a disease and show few or no signs of it.
After epidemics were whittled down, the scientists came up with the following calculus:
- The number of viral spill-over events of these four viruses from animals to humans increased by 5% annually from 1963 through 2019.
- Deaths from these four viruses increased by about 9% each year during that period.
- In 2020, the four viruses likely caused about 1,216 deaths combined.
- If the rate of growth continues, four times the number of outbreaks will occur by 2050.
- Those outbreaks will cause 12 times the number of deaths—around 15,000 a year.
The figures are likely an underestimate, the authors cautioned.
Most of the 72 outbreaks they examined were caused by filoviruses in Africa like Marburg and Ebola, which comprised more than half of outbreaks. The duo of viruses caused more than 90% of the 17,000-plus total deaths.
While SARS was the No. 2 leading cause of deaths, at 922, it caused a significantly smaller amount of infections, mainly impacting Asia—as did the Machupo and Nipah viruses, which caused 529 deaths combined, mainly impacting South America and Asia.
‘Urgent action is needed’
The researchers’ findings suggest that spill-over events “are not an aberration or random cluster, but follow a multi-decade trend in which [such] epidemics have become both larger and more frequent,” the authors wrote, adding, “urgent action is needed.”
“One of the most important things we can continue to do is early detection and intervention, which has been shown time and time again through research to be one of the most effective ways to limit the start of an outbreak,” Amanda Meadows, a data scientists at Ginkgo and lead author of the paper, told Fortune.
During the pandemic, collective gains were made in wastewater surveillance. COVID is now widely monitored in wastewater, as are other diseases like flu, RSV, and even Mpox (formerly known as monkeypox). An ideal scenario: if pre-existing wastewater surveillance systems are able to screen for potential pandemic pathogens like Ebola, Nipah, and others, giving experts a warning that an outbreak may soon occur, Meadows said.
Even if widespread wastewater surveillance isn’t economically feasible, wastewater programs at major international airports like those stood up during the pandemic could alert public health officials to the arrival of such pathogens from overseas, Nita Madhav, senior director of epidemiology and modeling at Ginkgo, told Fortune. It’s crucial, she added, that the world maintain the surveillance structure built during COVID for use during future pandemics.
Both Meadows and Madhav said they hope researchers and the public alike don’t fall into the classic pandemic panic-neglect cycle that ensures the world is never quite ready for the next global health catastrophe.
Aside from maintaining and even improving on the surveillance network built during the COVID pandemic, Madhav said there’s more that can be done to prevent future pandemics, including small changes made on an individual level.
How consumers can fight climate change
Pandemics and epidemics “are not a foregone conclusion,” Madhav said, “if we can reduce drivers of risk like climate change, and implications of human interaction with land. It’s really powerful that people can make personal choices that directly impact how this plays out over the next decades.”
Some actions consumers can take to reduce climate change, according to the United Nations, Natural Resources Defense Council, and Imperial College London:
- Conserve energy and water. Much of the electricity, heat, and water we use as consumers involves the use of coal, oil, and/or gas. Dress more appropriately for the weather to reduce your heating/cooling needs. Weatherize your home. Take shorter showers. Turn off the water while washing and/or brushing. Switch energy-efficient appliances and WaterSense fixtures and appliances. Unplug items you’re not using like TVs and vacuums, and/or turn on energy-saving mode. Wash your laundry with cold water. And hang your laundry to dry. You can also improve your home’s energy efficiency by replacing oil and gas furnaces with an electric heat pump.
- Switch up your energy sources. See if it’s possible to tap into wind and/or solar power to generate the energy your home needs.
- Rethink transportation. Walking, riding a bike, and driving an electric car can reduce greenhouse gas emissions. So can car-pooling and working at home, when possible, if it means forgoing a commute in your car. Airplanes, like cars, burn fossil fuels. So consider taking a train, making fewer flights, or meeting virtual.
- Shop mindfully. Consumer products like electronics, clothes, and plastics generally generate carbon emissions at multiple points in production. Buy less, buy second-hand, and repair when possible. And remember that when you spend money, you’re voting with it. Support environmentally conscious companies when feasible.
- Give your diet an edit. Shifting to a vegetarian or mixed diet can reduce your carbon footprint. That’s because plant-based foods like fruits, vegetables, whole grains, legumes, nuts, and seeds require less greenhouse gas emissions to produce than do meat and dairy. Keep in mind, too, that when you throw away food, you’re wasting more than just food—you’re wasting the resources used to produce it. Don’t purchase more than you need. Eat what you have at home, and compost leftovers. If you garden even minimally, plant native species, for reasons explained here.
- Use your voice. Petition leaders at all levels to take action to reduce climate change. Vote for candidates who realize the importance of environmental issues. And talk to friends, colleagues, and neighbors about the changes you’re making. Perhaps your actions will inspire them to similar ones.