Transcript of Get Ready Report podcast Episode 8:
“Zoonotic Diseases, Part 1“
Interview with Lonnie King, DVM, director of the National Center for Zoonotic, Vector-Borne and Enteric Diseases at the Centers for Disease Control and Prevention
The word zoo makes most of us think of the zoo, but of course it means something else. What are zoonotic diseases?
“Zoonotic” is not a bad thing to think about because it does mean animals, but the rest of the term, “-nosis” is actually Greek term, it means disease, So if you put them together, it is “animal diseases,” but it has, over time, really meant those diseases that are naturally occurring, that can be transmitted from or through animals to people.
How far back in recorded history can zoonotic diseases be traced?
They could be traced a long way back. Perhaps the first major group of zoonotic diseases probably occurred 8 to 10 thousand years ago and that was during the time of the advent of agriculture where communities were built because populations were stabilized and diseases were more easily spread. It was also at that time that animals were domesticated and for the first time in history that animals and people were brought together in close quarters and that was the first group of zoonoses, or zoonotic diseases. We also see references from ancient civilizations and their recordings from Babylon to the Nile Valley, China, even in the old testament. And writings of Hypocrites and Virgil, who wrote centuries ago, actually had references to this group of diseases.
What about in medieval times?
In medieval times, there are a lot of references and that was of course mainly because of the disease “plague,” which was a very significant event in history in terms of perhaps 25 percent of the world's population being wiped out by a zoonotic disease called “plague.” It is transmitted by an organism named “Yesinia pestis,” and it is actually transmitted through a vector or a carrier, which is the flea, and it resides mostly on rats. So as commerce picked up especially along the silk route, it went from Asia into the populations of Europe, and rats actually hitchhiked along the way. We actually transmitted that disease into huge urban populations in Europe. It was a very significant time in history, but it was definitely a zoonoses or zoonotic disease that came from animals to people.
Is it true that appproximately 70 percent of human infectious diseases are animal related?
In the last 20 or 25 years, we term this as the age of emerging infectious diseases. During that 2 to 2.5 decades, approximately 75 percent of the new human diseases that emerged are zoonotic. We look back and, of the 1,461 human pathogens that we know about today, about 60 percent or what we would term multi-host pathogens – in other words (pathogens that) don’t reside just in people by themselves. There is actually contacts through animal or animal products or even plants that actually are responsible for what we call multi-host diseases. But in the last 2 to 3 decades these emerging or reemerging diseases are primarily zoonotic and we estimate it’s about 75 percent of those.
What are some common zoonotic diseases?
The common ones that people probably think about are, of course, rabies, which we see worldwide, and a disease called “brucellosis,” that we just are in the process of eliminating from the United States, found in cattle and goats. One of the forms of tuberculosis in cattle in particular, called “mycobacterium bovis” was probably responsible for 25 to 30 percent of all the tuberculosis cases in the United states prior to pasteurization. Pasteurization will kill this organism, but in other parts of the world mycobacterium bovis is actually seen as one of the forms of tuberculosis. I think people understand Lyme disease and what’s happening in the northeast part of the United States and how that is spreading. Other diseases are leptospirosis, tularemia tularemia, west Nile virus and a lot of the food borne diseases which are kind of indirect ways of transmitting these diseases, salmonella and E coli 15787, campylobacter and listeria are examples of zoonotic diseases not directly (coming) from animals to people, but from animal products to people.
What animals would most commonly play a role in these infectious diseases that would spread to humans?
A lot of it depends on the contacts of people and animals. Our pets that we have can be responsible for some of these. Certainly the transmission from livestock and poultry, especially through indirect methods, through food and potential waterborne contaminants and also wildlife, tends to be [from] a group of animals that are more important in the spread of these diseases. West Nile actually resides in birds and mosquito cycles and Lyme disease is a kind of a complex-like cycle with ticks that involves white tail deer and rodents as well.
What simple measures can we take to reduce the risk of zoonotic disease transmission?
I think a lot of it is common sense. You need to avoid inappropriate contact when you’re out walking around and in the summer or warm months when there’s mosquitoes and you worry about west Nile virus or other mosquito-transmitted diseases. You need to use repellants and be careful at dusk and the kinds of things you wear. For ticks, it’s frequent checks when you’re outside in potential tick infested areas. Wear tight clothing and check and make sure that ticks aren’t on you. For pets, they should be treated for fleas and ticks. By taking them off of our pets we actually eliminate that transmission potentially to us. Vaccinating our pets. We no longer have canine rabies in the United States because of a good vaccine. We have rabies in bats, foxes and raccoons, but we don’t have them in dogs anymore. But vaccinations for things like leptospirosis is another way of reducing the risk. Taking your pets to the veterinarian to make sure they are free of pests. Getting dewormed, roundworms and hookworms and tape worms are potentially transmitted from our pets. Handling foods properly where you don’t cross contaminate in the kitchen. And you wash your hands frequently. And you cook foods to the proper temperatures like 165 degrees for meats and hamburgers . I think the last thing is just “handwashing,” “handwashing,” “handwashing.” It’s good hygiene, and that is probably the single best deterrent for transmission of many of these diseases.
Interview conducted July 2008 by Teddi Dineley Johnson, The Nation’s Health, APHA
"Zoonotic diseases: Part 2"
Part 2 of this interview is available as a Get Ready podcast.
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