Zoonotic Diseases and How a Bat Causes a Global Pandemic

In the wake of the SARS-CoV-2 pandemic, many questions about disease, sanitation, and vaccinations have emerged. A popular one out of the many is ‘how did bats cause the coronavirus?’ and the answer is that SARS-CoV-2 is a zoonotic disease that was transmitted to humans from bats.

What is a zoonotic disease?

A zoonotic disease is any type of infectious disease that is transmitted between humans and an animal species. These types of diseases are most commonly spread through direct contact with an infected animal, but there are also indirect ways of transmission. The disease can also be passed through contact with an infected animal’s food or water supply or through bugs, such as mosquitoes that may bite a human after coming in contact with the infected animal. Because of these transmission pathways, zoonotic diseases often arise in areas where there is shared land between humans and animals, such as farmlands or near forests. SARS-CoV-2 is just the latest in a list of known zoonotic diseases, including rabies, H1N1, lyme disease, Ebola, the black plague, and more. 

Why are zoonotic diseases so dangerous to humans?

It would be incorrect to claim that zoonotic diseases are always more dangerous than other categories of disease, but there are certain characteristics that zoonotic diseases have that cause severe effects in humans. Although the animal species can often survive a specific disease because of exposure to similar disease, the human immune system has not had exposure to these types of pathogens before. For this reason, the human immune system is not prepared to protect against these bacteria or viruses that originally infect other species. This also makes the emergence of zoonotic diseases very unpredictable. There are plenty of diseases in animals that never transmit to humans, and it is almost impossible to determine when, where, or from what animal these zoonotic diseases will infect humans. This makes it hard to prepare for and prevent. Another challenge that zoonotic diseases have is the possibility of re-emergence. It may be a common misunderstanding that once a vaccine is created against a disease then we should be able to get rid of that disease. However, only one disease has been completely eradicated in all of human history.  For zoonotic diseases, it can be even more difficult to get rid of them because the disease survives in the animal species, or what is called as the reservoir. Even if there hasn’t been a significant number of human cases, the disease can transmit into humans again from the reservoir. For this reason, there has been a recent push to increase surveillance of animal species that commonly transmit zoonotic diseases.

What may the future of zoonotic disease look like?

Of emerging diseases, it has been estimated that three quarters of them have been a type of zoonotic disease. This may be due to the increase of interactions between humans and wildlife particularly from the expansion of human populations into animal habitats. Despite the increasing risk of these diseases, there are no extensive strategies for preventing or controlling the emergence of zoonotic diseases. There has been a push for increased surveillance for early detection, improvement in preparation techniques, and better educational and behavior intervention to limit the transmission and spread of these zoonotic diseases. However, without changes these diseases pose one of the most severe health risks to humans.

For more information, check out these articles:

https://www.contagionlive.com/news/zoonotic-threats-as-unpredictable-as-they-are-dangerous

https://www.ncbi.nlm.nih.gov/books/NBK215320/

http://www.emro.who.int/about-who/rc61/zoonotic-diseases.html

For viruses in general, look into a video series called “this week in virology”

https://www.microbe.tv/twiv/

Published by Alexa Lauinger

I graduated from the California Institute of Technology (Caltech) in 2020 with a major in biology and a minor in environmental science and engineering. I worked in a biochemistry lab for three years. I was president of the Questbridge chapter at Caltech. And I played on the intercollegiate volleyball, basketball, and track team.

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