Navigating Zoonotic Diseases and Their Role in Human Health
Zoonotic diseases are shrouded in mystery—which means it’s an active branch of science where more researchers are needed in order to determine the origins of these diseases and to look at other factors such as how they spread, how to prevent the spread, and how to treat these diseases in both animals and humans.
Working in this field can be incredibly rewarding. It’s a career that is beneficial not only in terms of personal and professional satisfaction but also fulfilling in a global sense.
“People in this field are helping humans and animals alike as they uncover more information about these diseases—and they’re working for the betterment of ecosystems around the world.” – Dr. Robert Adamski, Associate Professor of Captive Care at Unity College
Below, you’ll find more information about zoonotic diseases and how to start down a career path in this field.
What is a Zoonotic Disease?
Zoonotic diseases are a complex beast—but their definition is pretty simple. These are diseases that have their origins in animals but are able to pass on to humans. They’re actually quite common throughout the world, present in viral, bacterial and fungal forms. Many of them can cause mild illness, but some can be severe and even cause death.
Just how many diseases are zoonotic in origin? About 60% of infectious disease worldwide are zoonotic, with three out of every four new diseases in people originating with animals.
How Do Germs Spread from Animals to People?
In many cases, zoonotic disease, whether bacterial, viral or fungal in nature, spreads to people through contact with animals carrying the disease. It can happen when handling, petting or even getting bitten or scratched by an animal. Because of this, people who are exposed to animals a lot—such as those working in animal care or in livestock—tend to be more susceptible to these diseases simply because they’re so often in contact with animals. Food can be a source of zoonotic disease, as well, which is why it’s advisable to cook eggs and meat to proper temperatures and only use pasteurized milk. Contaminated food can result in an infection.
Other sources of these diseases can be pets and contact with wild animals via hunting. Sometimes even spending time in areas with wild animals can result in the jump between animals and humans. This can happen when a person comes into contact with water or surfaces where infected animals may have left behind germs. In the case of hantaviruses, these can be spread through the air through aerosolized fecal matter produced by infected rodents. One vector for hantaviruses is something as simple as sweeping up dirt in an area where infected rodents have left droppings.
Sometimes there is also a third party in the transmission of zoonotic diseases. Lyme disease is a good example of this. Ticks pick up the disease from infected animals and then transfer it to humans when they bite. Fleas and mosquitos also commonly transfer disease in this way.
Examples of Common Zoonotic Diseases
Because zoonotic diseases are so common, the zoonotic disease list is long. Here, you’ll find examples of a few of the more common zoonotic diseases:
- Salmonellosis: This comes from the salmonella bacteria that is sometimes found in contaminated food. In these cases, food is contaminated when it comes into contact with infected feces. It’s one of the most common bacterial infections in the United States, though symptoms are typically mild with people recovering in two to seven days.
- Type A Influenza: There are four types of influenza, with type A influenza coming from horses, ducks, chickens, pigs, cats and even whales and seals. This is the only type of influenza known to cause flu pandemics. Type A and type B influenzas both can cause seasonal epidemics—although type B is not zoonotic because it only circulates among humans.
- Coronaviruses: These are the viruses on everyone’s mind right now with the COVID-19 pandemic. This virus family originates in birds and mammals, and they’ve been responsible for several different outbreaks throughout history. The SARS pandemic of 2002 and 2003 is one example, and today’s COVID-19 comes from the SARS-CoV-2 virus, which is another member of the coronavirus family that may have come originally from bats.
- Lyme Disease: This is typically passed from animals to ticks and then on to humans. In the United States, it’s the most common vector-borne disease, usually transmitted by deer ticks who picked up the Borrelia bacteria from animals like mice and deer.
- Rabies: This one comes from mammals like bats, raccoons, fox and skunks—though unvaccinated dogs can carry it, as well. It spreads from the bite or scratch of an infected animal. As diseases go, it’s a particularly severe one that causes brain inflammation which can result in death if not treated early, which is why it’s recommended to visit a doctor immediately after a scratch or bite.
- West Nile Virus: This is a mosquito-borne disease found in the United States. In most people, it doesn’t cause symptoms, but about one in five will develop a fever or other mild symptoms. One in 150 can develop serious illness. Using insect repellent and wearing long clothes are key methods for preventing this virus.
Risk Factors for Zoonotic Disease
Between salmonella sometimes infecting food and day-to-day contact with animals and their habitat, anyone can be at risk for zoonotic diseases. However, some people in certain environments or lines of work are at a higher risk. Livestock handling or working in markets where wild animals are sold are two examples of groups at higher risk for catching zoonotic diseases.
Zoonotic Disease is a Growing Concern
One of the biggest reasons why these diseases are a growing concern? Because they’re growing in frequency. No one is sure yet why these diseases are on the rise—but one theory is that humans are coming into contact with animals and their habitats more, which increases the chances of zoonotic disease making the jump from animal to human. Cultural and societal practices may play a role, too. More people hunting, developing uninhabited areas or logging drives animals to go farther in search of food and habitat. This results in stress for the animals, which makes them more susceptible to disease—and some of those diseases can then be transferred to humans.
This is paired with the fact that it is challenging to predict where these diseases will appear. All told, zoonotic disease is causing a lot of uncertainty.
How to Prevent Zoonotic Disease Transmission?
It’s easy to get scared by the idea of zoonotic diseases—and this can drive people to curtail their contact with animals or limit their involvement with the natural environment. But the reality is, the risk of zoonotic disease transmission is relatively low in most areas.
That said, there are ways to prevent transmission. Awareness is key: Learning about what zoonotic diseases may be prevalent in your area and how they are transmitted can help limit their influence. Lyme disease, for example, comes from deer ticks, so when hiking in an area where deer ticks live, it’s wise to take precautions like wearing long pants and checking to make sure you didn’t pick up any ticks.
Hygiene is also important. Wash your hands with soap and clean water after spending time with animals. Where pets are concerned, make sure to get them vaccinated to reduce the chances of them picking up a disease that can be transmitted to you.
Pursuing a Career in Zoonotic Disease
The field of zoonotic disease offers a chance to make a real difference in the world. These diseases crop up all the time, some of them affecting large swathes of the population—something we saw first-hand with COVID-19.
In this field you’ll be helping not only humanity as a whole, but wildlife and domestic animals, as well as the environment, since all of these things are inextricably intertwined. There is even some research suggesting that climate change is causing an upswing in zoonotic disease, and that means research in this field not only benefits society and ecology, but could possibly place you in a position to work toward finding solutions to the largest challenges the world faces today.
Working in the field of zoonotic epidemiology will require a solid foundation in animal science, biology and chemistry. These types of jobs often call for a master’s degree in epidemiology, but the path to a master’s degree can be paved with a bachelor’s degree in animal science or in animal health and behavior. Search among programs that offer a background in science, biology and animal science to pursue a career in zoonotic epidemiology.