Spotlight: Dr. Michele Miller on TB in Wildlife – Part One

dr michele miller
Dr. Michele Miller, Chief Veterinary Officer and Director of the Center for Conservation Medicine at the Palm Beach Zoo

When we think of infectious diseases, such as HIV or Tuberculosis, we usually consider them to be a human problem – there are rarely reports of disease in animals, unless it impacts people directly. The reality, however, is that infection greatly impacts domestic and wild animals, greatly affecting the health of our environment.

One of the leaders in researching tuberculosis in animals is Dr. Michele Miller. She is a Chief Veterinary Officer and Director of the Center for Conservation Medicine at the Palm Beach Zoo.

Dr. Miller holds a B.S. in Physics and Zoology, an M.S. and Ph.D. in Veterinary Science, and a D.V.M., from the University of Wisconsin. For the past eleven years, she has served at Disney’s Animal Programs in Buena Vista, FL, where she was Veterinary Operations Manager and staff veterinarian. Prior to joining Disney, she worked at North Boulder Companion Animal Hospital, Busch Gardens – Tampa, the Los Angeles Zoo, Animal Emergency Clinic of San Diego, and the San Diego Zoo. She was also Program Director and Faculty Veterinarian at San Diego Mesa College.

We recently chatted with Dr. Miller to get a better understanding of tuberculosis in wildlife populations and its potential impact on the environment. We will post excerpts from this interview in several parts. Below please find part one of our interview with Dr. Miller:

Is tuberculosis as prevalent in animals as it is in humans?

Tuberculosis is actually considered a re-emerging disease and it has been problematic for wild animals for a very long time. In fact, it has been recorded in elephants for more than 2,000 years. There are different strains of TB that can infect animals including the micro bacterium tuberculosis, which is the form of TB that we find in humans. Further, there are some strains of the disease that come from domestic animals, particularly cattle, which can spill over into wildlife and cause devastating consequences.

Do elephants, or other wild animals, experience the same symptoms as humans?

It really depends on the species. In elephants, they often will go on for years with an infection and not show clinical signs. Those that do develop clinical disease show similar types of signs as humans – weight loss, for example. They may also have respiratory disease, which would be coming from their trunk. Or, they might have discharge from other places where they are infected.

Some animals, such as white tailed deer, have been infected from domestic cattle. Again, these animals may not show the clinical signs of the disease. Currently, there is a situation in South Africa in which tuberculosis spread from domestic cattle into the African Cape buffalo. Those animals show very similar signs to what you see in domestic cattle, which is a wasting, respiratory disease.

Unfortunately, because many animals feed on Cape buffalo, those different species are now becoming infected and threatened, including the lion population.

Where is the incidence of tuberculosis in wildlife most prevalent?

It is a worldwide disease, just like it is in humans. We have wildlife populations here in the United States, particularly wild deer populations, that are infected with tuberculosis. We see tuberculosis in a whole variety of captive wildlife, especially elephants. Forms of tuberculosis affect birds and amphibians, reptiles and fish as well.

We see a higher incidence in Asia and Africa, and we also see it in Europe and New Zealand. We have not yet closely studies wildlife in Central and South America, but from the preliminary information we have, it does appear that those populations are also affected.

What it is about tuberculosis that makes it so contagious – even among different species?

It’s a pathogen that has been around for a very long time, and that has evolved to infect different hosts. It is also unique because it does not cause acute disease and acute fatalities in most cases – the animal or person can be infected and shedding the bacteria for years before being treated. These animals often live for a very long time and the disease is unlike other viral diseases where wildlife become infected, show clinical symptoms and then, in a short as a few days or weeks, recover or die. The fact that this is a smoldering, quiet disease makes it more contagious and an extremely difficult pathogen to fight.

Has there been any evidence of transmission between humans and animals?

There are some published reports of transmission between people and animals, particularly pet animals. We suspect that the tuberculosis in our captive elephant population initially came from people, as opposed to the animals infecting humans. In this instance, we have a very long-lived species that is in close contact with humans – if the humans are shedding the bacteria, then it is possible the animals contracted the disease that way.

Unfortunately, it is hard to track. Wild animals are very good at hiding signs of disease and infection. We do not have many validated diagnostic tests for many of these species, so it is often very difficult to know if an animal is infected until they are in the late stages of the disease. Sometimes, it can actually linger for years before we can detect clinical signs.

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Stay tuned to hear more from Dr. Michele Miller on the incidence of tuberculosis in wildlife and its impact on the environment…

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