Many institutions attempted to link the current health crisis to environmental degradation. What are the links between pandemics and the environment?

This is what the book by Sonia Shah, a renowned science journalist, entitled Pandemic*, explains through evidence. The author goes back to history, those of medical science and human societies, to explain how past epidemics appeared and how human activities on the environment played a decisive role, although often poorly recognized. 

To start, over the past 50 years, more than three hundred infectious diseases have emerged or re-emerged in places where they had not existed before. Years before the first cases of COVID-19 in Wuhan, 90% of epidemiologists predicted the inevitability of a new pandemic, caused by a known virus or a brand new one such as the current coronavirus.

Then we all carry a lot of microbes in us, so do all the other species. When these microbes remain in the body in which they evolved, they do not cause disease. Thus, neither Ebola nor coronavirus make bats sick. By contrast, they cause diseases in our bodies because they are new to us – they exploit a new habitat. The exchange of pathogens goes both ways – from animals to men and vice versa. According to Shah, our environmental policies have built shorter roads between us and wild animals. By cutting down forests to build our cities, factories, or mines, we have destroyed the habitat of other species, sometimes even caused their extinction. Species that survive human action must be content with the remaining fragments of natural habitat or invade that of humans.

The first case of Ebola in 2014 was that of a two-year-old child in West Africa, who was playing near a tree where bats lived. These bats normally lived in the forest, but by escaping fire and saw, they came to perch in the trees near human dwellings…

The author also took the example of West Nile virus, a virus that comes from migratory birds in Africa. Ornithologists had known for centuries that these birds landed seasonally in North America, but the first case of fever did not appear there until 1999. For a long time, the species of domestic birds that met these migratory birds were diverse enough, including healthy populations of green woodpeckers and rattles, which are poor carriers of the virus. With urbanization, the diversity of birds has decreased, green woodpeckers and rattles have become increasingly rare and have been gradually replaced by crows and robins, which are generalist species capable to live in any type of degraded environment, and which are good carriers of the virus. That' is how a mosquito could have bitten an infected bird and then a human being, and thousands of people are sick every year in North America...

The case of Lyme disease, an infectious disease that is transmitted by ticks, is another clear evidence. This disease first appeared centuries ago. The author links the spread of the disease in the United States to the creation of suburbs and the resulting forest retreat over the past fifty years. This forest retreat disrupted the balance of species composition, and possums and chipmunks that inhabited the forest were replaced by mice and deer. It turns out that a normal mouse destroys 50 ticks a week against a possum that destroys hundreds and hundreds a week simply by grooming. Ticks had to find a new habitat and the disease spread across the United States...

According to experts, the current coronavirus came from bats and contaminated humans through an intermediate host that has not yet been identified but is suspected to have been found in the Wuhan live animal market...

To all this, we can add the impacts of climate change that, by disrupting the seasons and ranges of species, causing human migrations, may promote the emergence of new diseases or their reappearance in new and unprepared places. All this is made easier by the expansion of the global air network, the promiscuity of cities, the lack of sanitation in some cities, and so on.

Today our top and common priority is to defeat COVID-19, and I acknowledge the efforts made by the State, communities, the private sector, the civil society, citizens. Now we must get ready for the post-COVID-19. We need to understand that pandemics, like climate disasters, are linked to our huge ecological footprint on the planet. We have made extensive use of our natural resources and COVID-19 shows us today what the price is. For the future, we must renew our link with nature, respect the needs of other species, stop all illegal trade in species, preserve and restore natural ecosystems, preserve biodiversity.  By protecting nature, we protect ourselves.  

(*) SHAH, Sonia. Pandemic: Tracking Contagions from Cholera to Ebola and Beyond. Ed. S. Crichton. 2016. 288 p.