Tortoise in the Glass: Evaluating Health Problems

To you, a typical tortoise might look like this:

desert tortoise adult

But to me, a tortoise may also look like this:

desert tortoise tissue samples

I’m a veterinary pathologist, which means I spend a lot of quality time looking through a microscope at slides with tissues to try to evaluate health problems that show up as changes in those tissues. I can find dying cells, inflammation, various pathogens, scarring, thinning, thickening, bleeding, tumors, strange crystals, and unusual pigments. All of the changes help us understand the health problems affecting an animal.

At the San Diego Zoo Institute for Conservation Research, I work exclusively on tortoises that have died at the Desert Tortoise Conservation Center. Why bother? Well, it turns out that one of the best ways to figure out what health indicators most accurately indicate disease is to compare the information from the live tortoise to the changes we see in the tissues if the animal dies. The more we know about which tools work to predict severity and type of disease, the faster and more precise we are at identifying and helping animals at risk.

To get information from enough tortoises to allow good conclusions to be drawn, I need to look at a lot of slides. Since 2009, over 4,500 slides have been made of desert tortoise tissues, providing an invaluable resource for the understanding of disease in desert tortoises. Since November 2012, I’ve been describing the changes I see so that they can be correlated to what was found in the live animal. Thankfully, I haven’t been working all alone; Dr. Lily Cheng, another veterinary pathologist, volunteered to spend two whole months staring at a mountain of desert tortoise slides. Between the two of us, we’ve done more than 3,000 slides belonging to over 250 tortoises!

Are you curious about what sorts of things we see? Good! We are always on the lookout for bacteria or viruses that cause that most feared of tortoise infections: upper respiratory disease. This is more than just a head cold like people get and is a big factor in tortoise population decline. Some savvy souls may note that no light microscope can show an individual virus particle (you really need an electron microscope for that, since viruses are smaller than the wavelength of visible light). Conveniently, however, some viruses clump together to form rafts of virus particles. These are big enough to see with a microscope, just as you can see a patch of lawn even if you are too far away to pick out a single blade of grass. The virus most common and dangerous in tortoise respiratory disease (herpesvirus) forms these aggregations in the nuclei of cells, and they are called intranuclear inclusions.

Below are some cells from a tortoise that had severe upper respiratory disease. On the left side of the picture, you can see normal nuclei: round or oval purple shapes that look very speckled, like chocolate chip cookies. On the right side of the picture, the nuclei are bigger and have clumps of magenta in the center surrounded by a clear rim. They no longer resemble chocolate chip cookies at all. Those magenta blobs are viral inclusions from herpesvirus!

Herpes inclusions

The work continues at a good pace, and there are only about 1,300 slides left to look at. They weigh almost 7 kilograms (15 pounds) altogether. Wish me luck!

Kali Holder, D.V.M., is a postdoctoral associate in the Wildlife Disease Laboratories for San Diego Zoo Global.

One Response to Tortoise in the Glass: Evaluating Health Problems

  1. Hello, I am an elected member of the Charles Darwin Foundation’s General Assembly that works for the conservation and restoration of the Galapagos Islands. I work on the National Geographic Islander which is a expedition ship run in partnership by the Nat Geo Society and Lindblad Expeditions.

    As you probably know our famous giant tortoise Lonesome George died last July. He did much for advertising of our conservation efforts and particularly for our captive tortoise breeding program and all the tourists bemoan the fact that he died suddenly.

    But I have a new “famous tortoise” in mind! Super Diego. He was taken from Espanola Island to the San Diego Zoo and then returned to us to become a champion breeder. In a nutshell: from a remaining 15 adult Espanola tortoises that were taken to the CDRS in the mid 60′s we now have 2000+ back in the wild on Espanola Island.

    Anyway – this is all as backgorund for you to help me get in touch with someone who knows the history of the male tortoise that we now have in Galapagos that was returned to us by the San Diego Zoo.

    Will you please pass this message on to someone who works with your giant tortoises or send me contact info for someone who can help me get some info about the tortoise we now so fondly call “Super Diego.” His is a far more encouraging story than that of Lonesome George who was the end of a species….

    Thank you and hope to hear from someone soon! My cell number is 850-443-0746 in case someone wants to call me.
    Dr. Lynn Fowler