By Mariana Castro Azpíroz
In this 2020 alone: wildfires in Australia that lasted 79 days, the highest deforestation rate recorded for the Amazon, deadly floods in Africa and the imminent attack of the killer wasps. It looks like the trailer for a post-apocalyptic movie; unfortunately, they are the headlines that have filled the news in what is not even the first half of the year. Now, Immersed in a pandemic caused by the new coronavirus (SARS-CoV-2), we wonder how we arrived at this scenario that seems like the end of the world. If all these events have something in common, it is that they narrate an ecological catastrophe, the consequences of which we have not given the importance they deserve.
In search of the culprit
At the start of the health emergency, it was rumored that someone ate a bat sopita in China and thus the disease began to spread. Bats have a very curious immune system. They need to produce a lot of energy to fly, which generates an excess of the so-called reactive oxygen species that, among other things, produce inflammation. Therefore, the inflammatory response of these animals is remarkably low. The interesting thing is that many of the symptoms that appear in a viral disease are not caused directly by the virus, but by the inflammation that occurs when the immune system fights the attack; for example, the pneumonia that some patients with COVID-19 suffer from.
This means that bats, having a reduced inflammatory response, can have viruses replicating within them and never present a disease as such, which makes them an excellent center of diversification for viruses.. In addition, they have very powerful mechanisms to end a viral infection before it grows. If viruses that adapt to survive in these conditions become transmitted to another species, they are now more powerful and more likely to cause more aggressive disease. The key point here is that humans have fostered additional inter-species contacts, due to their illegal trade, introduction of non-native species, and habitat destruction. This makes it much easier for diseases to be transmitted from one species to another (zoonosis).
Bat: the hero the world does not deserve, but needs now
Painting the bat as the villain of the story generated a lot of misinformation and led to actions as drastic as Peruvian residents trying to burn these animals, for fear that they would spread the new coronavirus. But, for starters, bats are unlikely to have spread directly to humans. In past epidemics, we have seen that the virus must first pass through an intermediary, as was the civet in the case of SARS; and the camel, in MERS.
In reality, attacking bats is counterproductive because they play a crucial role in maintaining the ecological balance. Help fertilize the land and reforest. They are pest controllers. 70% of bat species feed on insects, including many that damage agriculture or spread diseases, such as the dengue mosquito. And those who eat fruit are pollinators: we owe them not only seeds and fruits that we consume, but other products derived from plants, such as fibers, woods, oils and medicines. Without bats we wouldn’t have bananas or tequila!
Pangolin: the new suspect
It has recently been speculated that the intermediate species in this pandemic was the pangolin: a small mammal that looks like an anteater with armadillo scales, and is in danger of extinction. How did you transmit this virus to humans? The answer is the trade and consumption of exotic species. Pangolins are considered the most trafficked animal in the world: 100,000 specimens a year are extracted from their natural habitat. Later, they are transported in overcrowded and poor hygiene conditions to be sold in Asia for the consumption of their meat as gourmet food and their scales for traditional Chinese medicine. So it wasn’t a bat soup, it was a pangolin soup.
The loss of species is very worrying and also generates other problems whose consequences we do not always have in mind. Viruses adapt to replicate in a specific species. If they infect a different species, they often do not survive. But if we give them enough opportunities to try again, they mutate into an infectious new host. If they are found in an ecosystem where there is great biodiversity, it will be more difficult for them to jump to the same species enough times to adapt. This is known as the dilution effect. However, the reduction in biological diversity makes zoonosis more likely to occur.
More aggravating factors
All of the above combined with the fragmentation and loss of habitats promotes the selection of invasive species that tolerate the urban environment, which means more contagions in cities. In fact, deforestation is the leading cause of emerging diseases. And to make matters worse, air pollution encourages health complications considered risk factors for coronavirus. The toxic particles we breathe weaken the immune system; in addition, they promote inflammation of the respiratory system; equally, make one more prone to both contracting the disease and escalation and severe symptoms.
In short, we have left our planet in unsanitary conditions, both for ourselves and for other species. Through changes in land use, destruction of ecosystems and mismanagement of species, humans promote a biological imbalance that results in, among many things, pandemics like the one we are experiencing today. The current situation is a wake-up call to take forceful actions; both at a societal and personal level, there is an urgent need to adopt a much more environmentally friendly lifestyle.
Mariana Castro Azpíroz studied molecular biology at UAM Cuajimalpa.
The Coronavirus entry: messenger of ecological disaster? It was first published on Sopitas.com.