Almost a year ago, a devastating report was published warning that there are one million endangered species in the world and that rates of disappearance are accelerating at an unprecedented rate as a result of human activities. Now, a study published in the magazine Proceedings of the Royal Society B. highlights the relationship between these processes and the spread of infectious diseases such as COVID-19.
According to the results, the mechanisms that lead to the decline of wild species populations also allow a greater transmission of animal viruses to humans, a process known as zoonosis. “The spread of animal viruses is a direct result of our actions on wildlife and its habitat,” explains lead author Christine Kreuder Johnson of the University of California, Davis (USA). "As a consequence, animals are sharing their viruses with us, and these actions simultaneously threaten the survival of species and on the other hand increase the risk of contagion. The disaster in which we are currently immersed has been caused by an unfortunate convergence of many factors, including this."
In order to obtain these results, scientists analysed the information of the 142 viruses in which zoonosis are known to have occurred, as well as of all the species involved in the process as possible intermediate hosts. Using information from the International Union for the Conservation of Nature’s Red List of Threatened Species, they examined species abundance patterns, extinction risks and underlying causes in the decline of their populations.
Three groups of species involved in zoonosis processes can be identified: firstly, domestic animals, which, because of their proximity to humans, are the vectors of the greatest number of viruses. Second would be those species well adapted to the more humanized environments, such as some rodents and bats, and that are also very common vectors. And finally, the threat species: those endangered by trade, hunting, habitat degradation and excessive urbanization are twice as likely to be vectors of zoonotic viruses as those threatened by other causes. The conclusion is logical, as they are species that would also have closer contact with man.
Biodiversity protects us from emerging diseases
In recent years, it has already been demonstrated that the loss of biodiversity modifies and increases the transmission of diseases through various mechanisms that generally have to do with the modification of abundances or behaviours of hosts and vectors. For example, in the case of tick-borne Lyme disease, it is thought that the increase in its incidence in the USA would have to do with the decrease of some populations of birds that under normal conditions served as a natural reservoir of the bacterium and contained the transmission. By increasing at the same time the populations of rodents, which are also transmitters, it would have favoured the jump to the human species.
We need nature to protect our health
Fernando Valladares, a researcher at the National Museum of Natural Science (CSIC), also warns of the consequences of environmental degradation, "The fault of this crisis is not for bats or pangolins, but for our new global habits in the midst of a simplified and impoverished nature that does not fulfil its protective effect, now that we need it so much," explains the scientist. "We are ignoring nature, but our health depends on it much more than we think. More viruses will come, as indicated by the World Health Organization, and some will be more lethal and dangerous than the coronavirus itself. There will be no health system that can contain them. Only a rich and functional natural system, with the appropriate levels of biodiversity, will be able to cushion the impacts of future zoonosis on human health", he concludes.
Foto: Macacos rhesus en Katmandú. Los primates se encuentran entre los taxones de animales con mayor probabilidad de albergar virus que podrían extenderse a los humanos. Los macacos rhesus son altamente adaptables a los paisajes urbanos, lo que los hace más propensos a transmitir virus a los humanos.