Introduction To Zoonotic Disease

By Kristi Ontiveros

It is important for anyone who deals with wildlife, in any capacity, to have a solid foundation of knowledge regarding species specifics. This includes their natural habitat, diet, socialization and health related issues of the particular animal.

One very important topic for animal caregivers is that of zoonotic disease. Knowledge of this issue is critical, not only to aid in the proper care of the animal, but also for the safety and protection of the caregiver.

What Exactly Are Zoonotic Diseases?

Zoonotic diseases are infectious diseases transmitted from animals to humans through various modes of transmission.  Infection can occur via a bite, scratch, inhalation of spores, or contact with infected animal tissues.  Though these are not the only routes of illness, they are the most common.

The actual number of catalogued zoonoses is unknown in part due to the fact that the classification of the pathogens (i.e. viral, bacterial, parasitic etc.) is extensive as well as is the rapid increase of newly discovered diseases referred to as “emerging infectious diseases or EIDs .

In this discussion we will look at a brief history of these illnesses, some of the most familiar zoonoses, some EIDs, as well as prevention measures.

For the Love of Dog... (and Chicken and Cow)

The relationship between human and animal can be traced back to the dawn of man. Not only did we live, hunt and eat with dogs we also came to share our homes with them. That’s not all.  Paleopathologists believe that the domestication of animals as well as the development of farming and agriculture gave rise to the emergence of zoonoses.  Living in close proximity to animals as well as consuming their meat exposed humans to a host of new pathogens to which they had no immunity. With each new species bred or domesticated, the exposure to new pathogens increased.

The EIDs of today can be attributed to several factors, including, extremely high exposure to viruses in close living proximity, the routes of migratory birds (Bird Flu), illegal exotic pet trade or animal movement (SARS), and even air travel (West Nile Virus).

You Know More Than You Think, But Did You Know...

The word zoonoses originated from the Greek words ZOION meaning animal and NOSOS meaning illness.

Zoonoses are classified by their causative agents and fall into one of several categories. Most of the diseases we are familiar with fall into one of the following:

Not all zoonotic disease comes from wildlife.  Some we can get from our pets, like mange, toxoplasmosis, cat scratch fever and leptospirosis. However, if a pet is healthy and kept safe these should be of minimal concern. Some, like toxoplasmosis from cats, should only be a concern during pregnancy, since it can be harmful to a developing fetus.

From There to Here - The Transmission Cycle

Some pathogens that cause disease in humans exist naturally in an animal host (the reservoir) without causing any illness to the animal. The germ may be shed in the urine, feces or tissue of the animal, then ingested by another animal (the vector), and transmitted to another species (the secondary or dead-end host).

In the case of a viral zoonosis, such as West Nile, the host is a bird, the vector is the mosquito. Mosquitoes are sometimes referred to as arthropod vectors, and the virus’ they carry are called arboviruses.  When the mosquito feeds on the blood of an infected bird, the virus settles and replicates in the salivary glands. It is then transmitted to a human host when the mosquito injects salivary fluid to take another blood meal. Humans are considered dead-end hosts since we cannot transmit the virus.

In contrast, a bacterial infection such as leptospirosis requires only direct contact with contaminated water, food or soil that is contaminated with bodily fluids of infected animals. Fungal infections include ringworm, which again requires simple contact with the animal. Yet another likely mode of transmission is through inhalation of spores such as Hantavirus.

What's Old is New

Emerging infectious diseases are always in the news it seems. West Nile Virus, SARS, and Bird Flu (H5N1) to name a few. However disconcerting as they seem, it is believed these germs have had a hold in nature for quite some time.  The emergence of these diseases can be attributed to the fact that our world is getting smaller and we are living in what some refer to as a collapsible society.  The interweaving of once separate cultures and the ease with which we now travel has opened up more avenues for these pathogens. Science has yet to identify all pathogens, however, emphasis must be placed not only on identification but also on containment. The ability to disseminate information faster has proven successful in this area and has kept emerging epidemics from becoming pandemics.

It is believed that Alexander the Great died from complications caused by West Nile Virus. He died in Babylon in 323 B.C.!

Prevention

Although these and many other illnesses are treatable with antibiotics, or antiviral medications, some can be quite serious especially to the very young, elderly or those with compromised immune systems. The best prevention is not to become infected in the first place. This includes the following tips:

WASH, WASH, WASH YOUR HANDS WITH SOAP AND HOT WATER!
IF YOU MUST HANDLE AN INJURED ANIMAL ALWAYS WEAR PROTECTIVE GLOVES AND EYE WEAR
WASH YOUR HANDS AGAIN
KEEP YOUR PETS VACCINATIONS UP TO DATE
IF YOU HAVE RESCUED A WILD ANIMAL DON’T ALLOW IT TO ROAM YOUR HOUSE OR PLAY WITH YOUR PETS OR CHILDREN BEFORE SURRENDERING IT TO A PERMITTED REHABILITATOR
WASH YOUR HANDS ONE MORE TIME
DON’T KISS REPTILES, CUTE AS THEY ARE –THEY CAN CARRY SALMONELLA
WASH YOUR HANDS ONE LAST TIME WHILE SINGING “HAPPY BIRTHDAY” TWICE (THAT’S LONG ENOUGH TO KILL MOST BACTERIA PLUS IT’S FUN!)

Since most symptoms of zoonotic infections are flu-like in nature, you should see your doctor if you fall ill with symptoms within 2 weeks of coming into contact with wildlife.

Some diseases are considered reportable to the CDC. Your health care provider should be informed if you have been camping, swimming in lakes or rivers, have travelled internationally, or have had contact with wildlife in any capacity.

Conclusion

This information is meant to inform, not alarm, as well as to illustrate the fact that germs have been around since the beginning of time and are not about to loosen their hold on nature. We cannot eradicate all of them, therefore, we must arm ourselves with a great deal of knowledge so that we can protect ourselves and the wildlife we have pledged to help.

For more information on zoonotic diseases please visit the following sites:

Centers for Disease Control

Texas Department of State Health Services

National Wildlife Rehabilitators Association

American Veterinary Medical Association

World Health Organization