What is the connection between Covid-19, monkeypox and Ebola? All are outbreaks of emerging viruses linked to “zoonoses”. More or less ancient, with or without cure and more or less dangerous for humans, these diseases and infections have exploded in the 21st century. And everything suggests that things are not about to improve. 20 minutes tells you all about this large family of viruses.
What are zoonoses?
We call “zoonoses” all diseases transmitted to humans by animals. In the list, we therefore include Sras, Mers, Ebola and avian flu, as well as zika, Covid-19, HIV and even monkeypox. For the “monkeypox” virus, infected animals, most often rodents, transmit it. Regarding MERS, it comes from camels in Saudi Arabia where it was detected for the first time in 2012.
The natural host of Ebola, first identified in 1976 in the Democratic Republic of Congo, is bats. Marburg disease, which causes severe hemorrhagic fever, was identified in 1967 in Germany and Yugoslavia following work on green monkeys. Finally Zika, chikungunya and dengue fever are all transmitted by mosquitoes and exploded in Latin America in 2015.
These are therefore originally infectious diseases that vertebrate animals can transmit to humans, but some even end up becoming specifically human, like Covid-19 which is transmitted between humans. According to the World Organization for Animal Health, about 60% of emerging diseases are of zoonotic origin.
Why are there more and more?
If it is the animals that transmit zoonoses to humans, it is however not their fault, but rather that of humans and more precisely their way of life. Appeared thousands of years ago, since man intensified his interactions with animals by domesticating them, they have seen their frequency greatly increase over the past twenty or thirty years. “The interface between humans and animals has become quite unstable,” says Dr Mike Ryan, emergency manager at the World Health Organization (WHO). “Disease emergence and amplification factors have increased,” he said.
In question, “the intensification of travel, which allows them to spread more quickly and in an uncontrolled manner”, underlines Marc Eloit, head of the Discovery of pathogens laboratory at the Institut Pasteur. But also the intensification of factory farming which increases the risk of the spread of pathogens between animals. Trade in wild animals also increases human exposure to the microbes they may carry.
Deforestation increases the risk of contact between wildlife, domestic animals and human populations. “When we deforest, we reduce biodiversity; we are losing animals that naturally regulate viruses, which allows them to spread more easily,” explains Benjamin Roche, biologist at the Research Institute for Development (IRD), specialist in zoonoses.
Climate change will also push many animals to flee their ecosystems for more livable lands, a study published in Nature warned at the end of April. However, by mixing, the species will transmit more of their viruses, which will promote the emergence of new diseases potentially transmissible to humans.
What are the risks for humanity?
“Today we have easy and rapid means of investigation which allow us to react quickly in the event of the appearance of new viruses”, reassures Marc Eloit, of the Pasteur Institute. “We are also able to develop vaccines very quickly”, as we have seen with the Covid-19.
But “a whole line of new diseases is likely to emerge, potentially dangerous. We will have to be ready,” warns Eric Fèvre, professor specializing in veterinary infectious diseases at the University of Liverpool (United Kingdom) and at the International Livestock Research Institute (Kenya). This means, according to him, “focusing on the public health of populations” in the most remote environments and “better studying the ecology of these natural areas to understand how different species interact”.
Since the early 2000s, the “One Health” concept has been put forward: it promotes a multidisciplinary and global approach to health issues with close links between human health, animal health and global ecological state. In 2021, France also launched the international “Prezode” initiative, which aims to prevent the risks of zoonotic emergences and pandemics by strengthening cooperation with the most affected regions of the world.