At least 13 species, from bats to gorillas, are hosts to the Ebola virus. Its geographical distribution —and, therefore, the areas of potential risk of contagion— is limited to areas of the western part of central Africa. But spurred on by climate change, they are moving into new territories, taking their pathogens with them. A study published Thursday in Nature It is now estimated that these animals will have up to 3,695 new contacts with other mammals from new regions of the continent. These encounters will cause more than a hundred viral transmission events. The authors of this research have made this same calculation for thousands of mammals that are migrating and believe that the danger of a new pandemic will continue to increase in the coming decades.
Science has been demonstrating a double (and even triple) response of animals to global warming caused by climate change. Many species are migrating to latitudes more in line with their thermal optimum (temperature to which they are accustomed). Others are moving to the higher areas of their environment to escape the heat (or to the deep sea in the case of fish). This geographical reorganization of living beings would be opening new ways for the spread and contagion of viruses. On the one hand, because it brings into contact species that previously did not share space. On the other, because many of them are genetically related, which facilitates the viral jump between them. This increased risk is what a group of scientists have investigated by combining the expected climate scenarios for the remainder of the century, the evolution of temperature ranges and the movements of 3,870 organized mammals classified by their genetic proximity.
Between 96% and 98% of the species will share space with at least one other species with which they did not share before in the next 50 years. This work predicts that there will be up to 316,000 new encounters between mammals that do not coincide now. Up to 15,311 virus transmission events between one species and another could emerge from them.
Biologist Colin Carlson, lead author of the study published in Natureinvestigates the connection between climate change and the emergence of infectious diseases in the georgetown university (USA). He draws a comparison reminiscent of the possible origin of the current coronavirus pandemic: “The closest analogy is with the risks we see in wildlife trafficking,” says Carlson. “We are concerned about these markets [de venta de animales salvajes] because bringing sick animals together in unnatural situations creates opportunities for emergency processes, as happened with SARS, which jumped from bats to civets and then from civets to humans,” he adds, to conclude: “But the markets it is no longer something so special; in a climate change scenario, those processes will be the norm in nature almost everywhere.”
“Species move towards the poles, but they do it together, so they don’t run into new ones”
Colin Carlson, biologist at Georgetown University, United States
Indeed, the increase in interspecies virus transmission events will occur anywhere on the planet. Most of the risk is concentrated in Southeast Asia, sub-Saharan Africa and South America, although events are also expected in Western Europe and North America. The concentration in tropical regions seems to contradict the direction of animal migrations towards higher latitudes attested by other studies. Carlson acknowledges that this result “completely” surprised them, but he sees a certain logic to it: “The species move towards the poles, but they do it together, so they don’t run into new ones”. That is, the movement towards higher latitudes does not imply a greater risk of virus contagion, because the number of new encounters is relatively low, since species that already shared space move in parallel. But the other great movement is altitudinal, that is, more local movements to elevated areas. That is where species from different areas are found. That is why his results indicate that the emergence of new infections is taking place in the highest areas of the tropics. “When they can move horizontally and reach the mountains from different sides, that’s when they may meet for the first time,” he details in an email.
Phylogeny, genetic closeness, is a key factor in a virus’s ability to jump between species. The more similar two animals are in their genes, the more likely the pathogen will find accommodation in new hosts. Greg Albery, organization researcher EcoHealth Alliance and co-author of the work, highlights, however, that most of the risk is contributed by the movement of animals to other areas. “Phylogeny is actually a more important determinant than geography in terms of influence, but it doesn’t change. Species never change their degree of closeness [genética] on the ecological time scale we are interested in [de 2020 a 2070]but they do change in their geographical distributions”, he details in an email.
The authors of the work emphasize that climate change has surpassed other anthropogenic alterations that traditionally affected the risk of contagion between species and, ultimately, to humans. Deforestation, agriculture and the extension of urbanization, in addition to reducing distances, introduce imbalances that facilitate the emergence of viral events. To reduce the danger, they propose matching surveillance systems for diseases in nature with real-time studies of changes in the environment that are taking place.
The problem is that, even by reducing emissions and the rate of climate change, it is still too late to stop changes in geographical range. Albery argues: “The reason is that they are already migrating, and have been doing so for some time. They will continue to do so for a while longer because even our best efforts will only delay the warm-up rather than reverse it, so they will continue to have the motivation to move.”
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