What are zoonotic diseases and what does the destruction of rain forest have to do with it?

Image credit: David DennisFlickr: Bat in a Cave. CC BY-SA 2.0.

Ebola, HIV, rabies and the Corona virus. They all are caused by germs that can spread between animals and humans, also called zoonotic diseases.

HIV most likely originated from chimpanzees that were hunted and eaten for meat.  Similarly, Ebola is linked to the consumption of bush meat, especially bats.

The infamous Corona virus is thought to have jumped species first at a ”wet market” in Wuhan, China. Wet markets are traditional places that sell dead and live animals out in the open. These markets pose a good opportunity for a virus to jump species because hygiene standards are low and they are densely packed with people. However, the exact animal source of the Corona virus is still unknown. But bats are suspected to be involved here as well by infecting chicken, which was then consumed by humans. These winged mammals are often a source of zoonotic diseases because they live in large groups and travel far distances.

Normally, it is not that easy for a virus to jump from one species to another. When an organism gets infected a virus hijacks its cells to make copies of itself. To enter a cell, the virus has a key-like structure on its surface that will only let it into the cells of one single species. However, during the copying process mistakes are made and mutations occur in the key-like structures. With some luck for the virus one of these mutations will enable it to enter the cells of another species, for example humans. The virus has jumped species. This process is easier if hygiene standards are low and places are densely packed.

Research by scientists from the universities of Bonn and Ulm (Germany) also suggests that the destruction of ecosystems like rain forests may enable infections to jump species more easily. The researchers looked at ecosystems in Panama comparing undisturbed rain forest, smaller rain forest islands in the Panama Canal and small islands of rain forest within in an agricultural landscape.

Biodiversity is reduced in these small rain forest islands compared to intact rainforests. For example, there are fewer species of bats and rats. Therefore, individuals of the same species live closer together and are less dispersed. The results of the German research team showed that this also made it easier for different kinds of virus to spread within the populations of the remaining rats and bats giving these germs larger reservoirs. This could in turn make it easier for a virus to jump species and infect humans.

It is quite astonishing that the destruction of ecosystems could indeed influence our health by increasing the risk of zoonotic diseases like Ebola, HIV and the Corona virus.



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