Researchers may never discover exactly which animal was the final host before SARS-CoV-2 jumped into humans, but they can say one thing with relatively high certainty: Similar crossover events of zoonotic viruses resulting in outbreaks are going to occur with increasing frequency — and kill more people each year — even if they don’t necessarily result in a global pandemic. Those are the findings of a recent study in BMJ Global Health that analyzed data on a very narrow subset of virus types and found that virus jumps from animals to humans are occurring more often.
Because the subset of viruses researchers investigated is so narrow, the study almost certainly underestimates how much zoonotic crossover events will increase over the years. Zoonotic diseases are transmitted from animals to humans after the pathogen successfully evolves to survive in humans. More than half of all infectious diseases that affect people can be spread from animals; about 75% of new and emerging infectious diseases begin in animals and cross over to human populations.
The new study found that the number of spillover events has been increasing by 5% each year; deaths from those spillover events have been increasing by 8.7% each year, though the higher mortality rate is primarily due to the West Africa Ebola outbreak in 2014-2016. Without that outbreak, the increase in death rates is 5.1% per year.
But even these rates are only tied to a handful of viral classes; they exclude the COVID-19 pandemic, established endemic diseases (such as mpox), vector-borne diseases (such as Zika), and influenza. It’s possible that including those viruses and others, as well as bacteria and fungi, would reveal an even greater increase in spillover events.
Reporting tips
Possible solutions to cover
The news isn’t all bleak, however, and that’s where journalists come in. “This trend can be altered by concerted global efforts to improve our capacity to prevent and contain outbreaks,” study authors note. They include a list of examples of proposals that could reduce risk of outbreaks:
- “Establishing systems for disaster risk financing to fund response measures.”
- “Creating an intergovernmental panel on pandemic risk to quantify, track and assess risk over time.”
- “Addressing the drivers of pandemic risk, including deforestation and climate change.”
- “Advancing the technology and infrastructure needed to detect and respond to public health threats, including surveillance programs” with passive and active surveillance tools.
Some programs, the authors note, have already been implemented as a result of the COVID-19 pandemic, such as increased investment and development of RNA vaccines, improved surveillance at key travel hubs, and increased wastewater and genomic surveillance.
The study method
Researchers analyzed data in a World Health Organization database of 3,150 outbreaks, looking for outbreaks and epidemics caused by viruses that occurred between 1963-2019 and killed at least 50 people. They focused specifically on filoviruses (Ebola virus and Marburg virus), SARS coronavirus 1, Nipah virus and Machupo virus, as these have “the potential to pose a significant risk to public health, economic, or political stability.” They identified 75 spillover events in 24 countries, resulting in 17,232 deaths.
“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,” the authors reported.
Excluded viruses
The authors excluded several groups of viruses to reduce the likelihood of bias, particularly surveillance bias, in their calculations. Knowing the virus categories they excluded and why can help reporters think critically about infectious disease outbreaks and crossover events that they report on.
The authors specifically excluded four categories of viruses:
- Viruses that have caused 100-plus cases a year for at least five consecutive years — such as MERS, Lassa virus, mpox and Hantavirus — were excluded because reporting rates and quality vary widely by country and region, and improved surveillance could result in an apparent increase that isn’t a true increase.
- Viruses that have caused fewer than 50 total reported deaths — such as Hendra virus, Lujo virus and Whitewater Arroyo virus — were excluded because existing testing and surveillance may be insufficient for adequate detection, which means improved testing and surveillance later on could produce an apparent increase that doesn’t represent a true increase.
- Vector-borne viruses — such as Zika, Venezuelan equine encephalitis and Crimean-Congo haemorrhagic fever virus — were excluded because the ways these viruses spillover from animals to humans differs so much from non-vector-borne pathogens, and programs aimed at controlling the vectors (such as spraying insecticide for mosquitoes or ticks) could affect the likelihood of spillover events.
- Influenza spillover events were excluded because existing surveillance programs for flu have expanded and improved over time, potentially confounding how much real rates of spillover have changed.
Story ideas and questions to ask
The study’s findings therefore present journalists with several opportunities for story ideas or questions to investigate:
- What programs exist or need to exist at the local, state, national and international levels to prepare for these inevitable outbreaks?
- How is funding for pathogen surveillance and public health response being allocated in local, state, national and international governments and organizations?
- What projects are occurring at the local, state, national, and international levels to address the underlying factors contributing to zoonotic crossover events?
- Solutions journalism: Are any organizations or local governments taking a proactive approach to public health surveillance or to reducing local contributing factors to zoonotic crossover opportunities? These could involve anything from local food safety protocols to stricter policies governing hunting practices to public school education programs to expansion of school nurses to programs aimed at reducing climate change effects.
- Service journalism: What can individuals do to protect themselves from zoonotic diseases, such as taking reasonable precautions around pets, farm animals and wild animals?
- Solutions journalism: What local or state programs are explicitly trying to reduce the incidence of infectious disease from pets, farm animals or wild animals to human populations?
Resources
- The CDC site on zoonotic diseases is a good place to reference for general information.
- The most comprehensive up-to-date resource for infectious disease outbreaks, including emerging pathogens, is ProMED.
- Zoonotic Diseases: Federal Actions Needed to Improve Surveillance and Better Assess Human Health Risks Posed by Wildlife, from the Government Accountability Office.
- Surveillance and Information Sharing Operational Tool from the World Health Organization.
- Strengthening global health security by improving disease surveillance in remote rural areas of low-income and middle-income countries, from The Lancet Global Health.
- Surveillance and response strategies for zoonotic diseases: A comprehensive review, from Science in One Health.
- Prioritisation of zoonotic diseases for coordinated surveillance systems under the One Health approach for cross‐border pathogens that threaten the Union, from the U.N. Food and Agriculture Organization.
- Surveillance and Information Sharing Operational Tool, from the U.N. Food and Agriculture Organization.
- National surveillance for zoonotic infectious diseases, from the American Veterinary Medical Association.
- Wildlife-borne Disease Surveillance, from the U.S. Department of the Interior.
