Facts on upper respiratory tract disease in tortoises and turtles are revealed in this exclusive interview with the world renowned scientist, Professor Mary B. Brown, Ph.D. She was part of a team that worked to identify Mycoplasma as the organism causing URTD in 1992. Professor Brown has continued to address new and difficult questions about the effects of this disease on tortoises and she contributes highly valued expertise to many organizations working to save tortoises. The interview took place in Palmdale on January 25, 2003 when Dr. Brown was visiting California and about to be honored by the Desert Tortoise Preserve Committee with the Golden Tortoise Award.
Stephanie Pappas (SP): Dr. Brown, thank you for interviewing with the Tortuga Gazette. As a scientist and tortoise hobbyist, I have been following your studies on Upper Respiratory Tract Disease (URTD) for several years. I consider you an expert on Mycoplasma, the organism responsible for URTD and have the utmost respect for your colleagues, Dr. Elliot Jacobson, D.V.M., Ph.D, Dr. Paul Klein, Ph.D, and Dr. Dan Brown Ph.D, all of whom have dedicated many years of their careers to studying disease transmission in tortoises. Can you comment on these individuals and where this research work is being done?
Mary Brown (MB): One of the important factors in studying URTD in Gopher tortoises is that this has been a team effort. I happen to be the person that has the Mycoplasma expertise, Elliot Jacobson has the reptile medicine knowledge, Paul Klein has the comparative immunology, and Dan Brown has the molecular biology tools. We accomplished what we have because we worked together, as a team, with each person combining their knowledge. We learned from each other and the team learned more together than we would have as individuals. Primarily, all the individuals I mentioned are currently working at the University of Florida. However, we have trained many individuals over the years that are now at different places doing similar work on the Gopher tortoise.
SP: Dr. Brown, you mentioned that most of your disease work at the University of Florida is being done on the Gopher tortoise, are you currently doing any studies on the desert tortoise (Gopherus agassizii)?
MB: An upper respiratory tract disease in Gopher tortoises is caused by the same organism, Mycoplasma agassizii (M. agassizii) as URTD in the desert tortoises. Many of the things we learn from the Gopher tortoise help the California desert tortoise, and vice versa. In fact, we just received a grant from a special joint program administered by the National Institution of Health and the National Science Foundation called the Ecology of Infectious Diseases. This five-year study will focus on factors that impact the severity of disease transmission in wild populations of the Gopher tortoise. The major factors we will examine will be microbial virulent factors (which means how the bacteria makes the animal sick and how the animal responds) and human impact on the habitats. We think this study on the Gopher tortoise will assist in determining the cause of deaths and decreased reproduction, and tell us how it effects different sexes, males versus females. The study of Gopher tortoise will also give clues as to what is happening with the California desert tortoise.
SP: For many years, I have heard a rumor that URTD originally spread in wild tortoise populations because someone released a captive desert tortoise back into the wild population and that tortoise was carrying a domesticated disease, now known as URTD, caused by M. agassizii. Do you believe this is a true fact?
MB: No, I believe that there is a lot of speculation and no scientific data. Clearly where you have captives released , you originated. We have seenM. agassizii disease in Gopher tortoises, Desert tortoises and Box turtles in wild populations. For the most part,M. agassizii tend to be host specific. That means that a specific Mycoplasma that will infect a cow will not infect a goat. Think of it as having a limited range of animals that a single Mycoplasma species can infect. From that stand point, you would not expect the organism to arise from a pet dog, but most likely evolved to fit inside the host, the tortoise. Mycoplasma lives very close to the host; these organisms do not survive in the environment very well, as a result, they developed a very close attachment to the host nasal surface.
SP: How do scientists know this?
MB: There are ways to test the hypothesis, and the more clinical isolates we have, the more we can determine using molecular tools. Molecular Epidemiology is a fancy way of saying we are going to look at what kind of chromosomes and genes there are to trace the history. The problem is, in evolution terms, that period evolved very quickly. OH, NO, this is going to be too complicated!
SP: Can we simplify this for our readers?
MB: What I mean is, if the disease started five years ago it would be easier to track. The fact that we first saw this disease 20 years ago means that too much time has passed and now it will be very difficult to determine exactly where it originated. The important thing is not where it originated, but how do we contain it and prevent more disturbances in the desert tortoise populations. The best way to contain and prevent the disease from spreading is NOT TO RELEASE CAPTIVE TORTOISES. Captive tortoises that have URTD can survive for a long time, because the owners provide good care of them and get them medication when clinical signs appear. The medication will not cure the disease, but will eliminate the clinical signs. The bottom line is if you have captive tortoises, please do not release them! Another thing, Mycoplasma is only one potential infectious agent causing clinical signs of URTD 's. One we know about! There may be other infectious agents out there that we do not know about yet, therefore, you do not want to risk spreading new disease to native, wild populations of tortoises.
SP: Dr. Brown, obviously tracing the origin and history of the disease is quite complicated! So let 's move onto how the etiology of this disease, M. agassizii, was discovered. Can you explain what etiology means to our readers?
MB: Etiology is a fancy way of saying what it is that makes the animal sick and causes the disease. There is a very defined scientific way to determine this. It's called Koch's postulate. To prove Koch's postulate, you find a sick animal and isolate an organism. You put the organism that you isolated from the sick animal into a healthy animal, induce the disease, and then get the organism back out of that animal. Basically, we have fulfilled Koch's postulate in both the Gopher and the desert tortoise confirming that M. agassizii causes URTD. What we are finding now is that we may have a complex of several very closely related Mycoplasma that may be responsible for respiratory disease; it may not just be M. agassizii. We have fairly good evidence that there is at least one additional organism, Mycoplasma cheloniae, that maybe involved in causing respiratory disease in tortoises. Mycoplasma respiratory disease is very common, it causes respiratory disease in humans, chickens, turkeys, pigs, rats, mice, goats, and cows.