Disease Outbreak, Infectious Diseases

Infectious Diseases Come from Animals? - Zoonotic Transmission

~Written by Theresa Majeski (Contact: theresa.majeski@gmail.com)

For those people who have been following the Ebola outbreak relatively closely or who have been doing their own research into Ebola, you may have heard that scientists think Ebola is introduced into the human population through fruit bats and/or the butchering of bush meat. 

This concept of infectious diseases passing between animals and humans is not new and is called zoonotic transmission. Now Ebola is a virus, but other disease causing agents such as bacteria, parasites and fungi can also be spread between animals and humans. While you may not have heard of zoonotic transmission before, I bet you’ve heard of some zoonotic diseases. Examples include anthrax, Lyme disease, Avian influenza, plague, malaria, dengue, West Nile virus infection, and rabies. The WHO says there are over 200 zoonotic diseases known to us thus far. I also bet you didn’t know that about 75% of recently emerging infectious diseases affecting humans are of animal origin and approximately 60% of all human pathogens are zoonotic. (I just learned these facts as well and am sufficiently surprised the numbers are that high). 

So how in the world does someone get a zoonotic disease? Well, for instance, anything transmitted by mosquitos or ticks are zoonotic diseases, so take proper precautions to prevent being bitten by all ticks and mosquitos. You can also come into contact with zoonotic diseases through petting zoos, pet stores, nature parks, farms, etc. Our beloved pets can also transmit diseases like salmonella, hookworm, and roundworm. The moral of the story is to make sure you’re washing your hands after handling animals and to be careful about petting every fluffy creature you come across. 

Now I would be missing a big part of the picture if I didn’t investigate some of the human-induced reasons why more and more of the population is in danger of being directly impacted by these “remote” zoonotic diseases. Zoonotic diseases transmitted by mosquitos for example, generally only impact people living in areas where those mosquito species are found. Climate change is allowing for some of these mosquitos to expand their territory, thereby bringing zoonotic diseases to new areas of the world. For example, two mosquito species known to carry malaria are now found at the US-Mexican border. Additionally, our expanding population and changes in how humans are migrating are causing interactions with species we’ve never encountered before through practices such as forest clear-cutting and wetland draining. 

I have no easy solutions to these problems as they stem from much larger human population growth issues. But the good news is that we, as humans, have noticed that zoonotic diseases are a growing issue and have stepped up efforts to stay on top of things. The European Union has passed legislation requiring member states to increase their monitoring of zoonotic diseases and has specific guidelines on how to do that. Self-proclaimed “Virus Hunter” Nathan Wolfe did a TED Talk on how his team and he are working on the frontlines of novel virus detection by using innovative ways to collect specimens, detect, and track previously unknown viruses in humans. (I highly recommend watching the talk even if you’re not really interested in emerging infectious diseases as it provides a practical look into the challenges of doing fieldwork in remote areas where these diseases are coming from.)

The important thing to take away from all this information is that zoonotic diseases are almost unavoidable as we humans are interacting with our world, and that world includes all sorts of known and unknown pathogens. By prioritizing innovative ways for early detection we can hopefully learn about potential diseases and create possible remedies before they become global pandemics