Want to limit the transfer of viruses between animals and humans? A new report gives examples of how to do that by keeping ecosystems intact.
The pandemic prevention road map, published March 26 in Nature Communications, recommends protecting or restoring places where animals forage and rest, and minimizing human-wildlife encounters in more developed areas.
Most outbreaks of previously unknown infectious diseases, like COVID-19 or HIV, are caused when a virus jumps from an animal to a human. That jumping is called zoonotic spillover. Wild animals stressed by food shortages or habitat loss become more susceptible to viral infections and may even shed more viruses.
Protecting forests, rivers and other natural spaces has already been touted as a cost-effective way to prevent pandemics (SN: 7/23/20). The new recommendations for mitigating spillovers — put together by an international team of biologists, ecologists and policy experts — are based on case studies of zoonotic spillover from bats.
After studying Hendra virus (which has killed four of the seven humans infected) in subtropical eastern Australia, researchers in 2022 reported that spillovers occurred when winter food shortages caused fruit bats to seek out flowering plants in urban gardens or agricultural areas. The virus jumped to horses grazing in areas where infected bats excreted urine or feces. Sick horses then infected some humans.
“Once you really understand how spillover happens, the solutions can become evident,” says Raina Plowright, a disease ecologist at Cornell University who coauthored both the 2022 study and the new paper. For instance, to prevent Hendra outbreaks, one strategy now being tested in southeastern Queensland is to replant five species of flowering trees. “Sometimes really small changes in an ecosystem can have really profound effects.”
Another way to “set ourselves up for success” to avert spillover, says road map coauthor Iroro Tanshi, an ecologist at the University of Washington in Seattle, is protecting wild places and “really honing in on breaking contact” with wild animal populations. In Nigeria, where Tanshi studies bats, she engages local communities in preventing human-caused forest fires and in providing people with alternative sources of protein to reduce the need to hunt bats in caves.
Bat species host four of nine diseases that have the greatest potential risk to public health, according to the World Health Organization. However, the road map’s tactics can “apply to other animals that can be viral reservoirs” like rodents, primates or birds, says coauthor Winifred Frick, chief scientist at the nonprofit organization Bat Conservation International based in Austin, Texas.
Ecological countermeasures such as those laid out in the road map may also protect animals from contracting viruses from humans. Viruses are twice as likely to jump from humans to animals than vice versa. After analyzing nearly 59,000 viral gene sequences associated with a variety of vertebrate hosts, researchers found that almost two-thirds jumped from humans while only about one-third jumped to humans, according to a separate study published March 25 in Nature Ecology & Evolution.
“The flow of viruses jumping between different animal species is an endless process,” says Cedric Tan, a microbial genomicist at the University College London Genetics Institute who led the viral sequence study. Tan, who was not involved with the road map, believes that “it is definitely worth exploring these measures,” although he cautions that it’s unclear whether ecological protections would reduce the risk of zoonotic jumps in all cases.
Plowright hopes that, alongside investments in biomedical and epidemiological technology to prevent future pandemics, decision-makers will simultaneously invest in conserving ecosystems to stop spillover from happening in the first place.
Her main recommendation for preventing the next pandemic? Reduce the number of roads into wild places. Roads pave the way for infrastructure development that destroys wildlife habitat, Plowright says. They also allow people to access animals and each other very quickly. Other researchers have demonstrated that higher road density increases the risk of Ebola infection, and that Ebola virus spreads along main roads.
Policy makers and public health officials should prioritize studying zoonotic spillovers before a virus becomes an epidemic or pandemic, rather than as “an afterthought,” Plowright says. “We should take every spillover as an opportunity to learn how it happened, figure out the drivers, and come up with solutions.”
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