Investigating Animal Deaths At The National Zoo

17:03 minutes

A woman wearing a tie dye pattern hairnet, cutting at a dead worm-like creature on a lab table.
Dr. Kali Holder, veterinary pathologist, dissecting a caecilian. Credit: © Kaden Borseth

When a critter meets its end at the Smithsonian’s National Zoo, it ends up on a necropsy table—where one of the zoo’s veterinary pathologists will take a very close look at it, in what is the animal version of an autopsy. They’ll poke and prod, searching for clues about the animal’s health. What they do—or don’t—find can be used to improve the care of living animals, both in the zoo and in the wild.

On stage in Washington, D.C., Ira talks with Dr. Kali Holder, veterinary pathologist at the Smithsonian’s National Zoo and Conservation Biology Institute, about her work, and they embark on a case of CSI: Zoo.

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Segment Guests

Kali Holder

Dr. Kali Holder is a veterinary pathologist in the Smithsonian’s National Zoo and Conservation Biology Institute in Washington, DC.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow coming to you live from GWU in Washington, DC.


When an animal meets its end at the National Zoo, it ends up on a necropsy table– fancy word for animal autopsy– where one of the zoo’s veterinary pathologists will take a very close look at it. They’re going to poke and prod and search for clues about the animal’s health, and what they do or they don’t find can be used to improve the care of living animals both in the zoo and in the wild.

And here to take us on a CSI-style investigation is Kali, Holder, veterinary pathologist at Smithsonian’s National Zoo and Conservation Biology Institute here in DC. Welcome to Science Friday.

KALI HOLDER: Thank you, Ira.


It’s great to be here.

IRA FLATOW: Kali, our theme today is national treasures. Why are dead animals a national treasure?

KALI HOLDER: Besides being animals, which are awesome, I love the mystery, the puzzle of dead animals. I also do biopsies. So I do pieces of live things and whole dead things, but no whole live things. Not that kind of vet. So I’m a veterinarian, and I work on these animals that have regrettably passed on, but we can learn so much about not only how our care is doing, but how we can improve their care and affect animals that are in other institutions or in the wild, even.

So for me, this is a great opportunity to just dig in. It’s the last chance we have to get the most information out of these animals about their health status so that we can improve what we’re doing, but also affect animals for conservation purposes.

IRA FLATOW: How many really cool cases– can you tell me about some of the coolest cases you’ve had?

KALI HOLDER: So in the last couple of months, I’ve had– I’ve been looking into some heart disease issues in some green tree pythons.

IRA FLATOW: Heart disease–

KALI HOLDER: Heart disease, yeah, in a snake. And I’ve been looking at some battle wounds in naked mole rats because cancer doesn’t kill naked mole rats, naked mole rats kill naked mole rats.

IRA FLATOW: Take-home message of this segment.



KALI HOLDER: I mean, we have everything from corals up to elephants in our collection. We’ve got bison, we’ve got animals from all over the world, and even aquatic animals–

IRA FLATOW: Do people send you animals that die that they wonder about?

KALI HOLDER: So we do everything that dies on property, not just our collection, but also wildlife that dies on property. So I will sometimes get animals that are wildlife that have died on property. And for a while, we had a fishing cat that was just a really good huntress– her name was Juniper. And so like I would get like half-a-bird, and they’d be like, here you go. And we do check that out because you never know why that bird might have been susceptible to being hunted by Juniper. I mean, the wrong place, wrong time.

But also, we’re looking for things like highly pathogenic avian influenza. We survey for that. We look for West Nile, that sort of thing. So we keep an eye on diseases that may be not just of animal importance, but also human importance.

IRA FLATOW: OK, so when you’re doing a necropsy, what do you actually look for? Take me through one.

KALI HOLDER: So, I friendly colloquially refer to it as unzipping. So I unzip the animal with a sharp object. And I’m going to be looking at every single organ. I’m going to see, OK, given how long ago this animal died– and usually we know because we look at our animals quite a lot– how bad is the decomposition? Usually it’s pretty good. It’s not a particularly bad decomposition. And then I’m going to look at all the different organs.

I have done a lot of animals, so I know what the normal colors and textures and sights and smells even are in all of these different organs. And so I’m going to take samples of all of those organs. But if I see anything already with just my naked eye– that’s called a gross examination. It’s not just like, ew, gross, but like, I can see it with my naked eye, I’m going to take a picture, make a note of that, and that’s all going to go into my gross report.

And then I’m going to take all of the samples that I took from all of those organs and I’m going to get them put on microscope slides, and I’m going to look at them under a microscope, and I’m going to see even more things under the microscope. And microscopy is actually beautiful, so I’m really excited that some of the pictures that we have today are photomicrographs that you’re going to get to see.

IRA FLATOW: And we’ll get to see them. First, though, I want you to tell me how you take what you learn and apply it to living animals.

KALI HOLDER: Right. So this is a great story here, where you discover something has gone terribly awry with the animal, and then you figure out what the cause of that is and it has major impacts for that species. So what has been rolled out on stage is a skull, but does anyone know what this skull– you can just yell what this skull might be from. We’re seeing a lot– we got whale, we’ve got bison coming– elephant!

Ah yes, so this is an elephant skull. Good job. Gold star to you! Excellent! Yes! This is an elephant skull. And if you’ve ever seen an elephant– it looks kind of small, and that’s because this is a baby elephant. So she was about 16 months old. She died in 1995. Her name was Kumari.

And Kumari had a terrible disease that caused her to bleed a lot inside and no one knew why. And the pathologists figured out that by looking under a microscope, that they saw characteristic lesions of herpesviruses, and they hadn’t recognized that that was a problem in elephants before.

But it turns out– this is actually what we would call like an index case. She was the first recognized death to be associated with specifically a herpesvirus. And herpes viruses are endemic. All of the elephants have at least one strain. Many of them have multiple strains. But it turns out that elephant endotheliotropic herpesvirus, which is what she had, is the most common cause of death in juvenile Asian elephants in human care.

And this was the beginning of figuring out that not only was this a really important cause of death for this species, but this was the beginning of understanding that we need to be able to detect this. So the National Zoo actually now has the National Elephant Herpesvirus Laboratory. They test samples from all around the country and even other places in the world. We help set up labs in range countries to help elephants in their native habitats because this virus is so important as a cause of death for baby elephants.

So Kumari is kind of a celebrity in the veterinary pathology community. And most people and most animals that have herpesvirus, it’s not usually a big deal. But if you’re a baby, it can be a big problem.

IRA FLATOW: Sad story.

KALI HOLDER: It’s a sad story.

IRA FLATOW: Now you see all kinds of critters–

KALI HOLDER: I see all kinds of critters.

IRA FLATOW: Including–

KALI HOLDER: Including this, which is one of my favorites. This is a Caecilian. Not–

IRA FLATOW: From Sicily?

KALI HOLDER: No. So this one is from Central America. These are legless blind amphibians. And so if you’re trying to figure out what’s going on here and you have ever seen the Princess Bride, it looks a little bit like a shrieking eel. Yeah, there’s just a tube of mucus-covered amphibian there.

IRA FLATOW: Very interesting description.

KALI HOLDER: Yes, thank you.

IRA FLATOW: And when I say tube– so snakes have a tail– there’s a mouth, hole, and there’s an anus, and then there’s tail after that. These guys don’t. It’s literally one hole at one end and one hole at the other end. They are just a tube. They’re great. And they have a lot of really neat adaptations, and they are a weird subset of amphibians, and I love them. They have teeth that literally do make them look like a shrieking eel, so that’s what that looks like.

IRA FLATOW: Looks like Alien.

KALI HOLDER: Yeah– yeah! I love them. So this is an adult. This is– aren’t they great?

IRA FLATOW: Why does it need all those teeth?

KALI HOLDER: Oh, because it eats a lot of invertebrates in the water and stuff. And so it’s just going around. But those teeth, they have tooth even when they’re in utero– sort of in utero. So this particular type of Caecilian is a live bearer. So they have babies that are in their oviduct, kind of like having a uterus, but they don’t have, really, a uterus, because they don’t have a placenta. And they’re just free-swimming.

Like, you may have heard of sharks doing this. Caecilians, some of them do this, too. So they’re just free-swimming in the parent, just doing their thing, and they have teeth. And they have big, floppy gills– they’re really adorable. And how they get their nutrition free-swimming in the oviduct is that they graze on the uterine lining. Yeah. Mom-nom-nom. They’re just– they’re just eating– I love that. They’re a little– little body horror creatures. I love them.

IRA FLATOW: When you get to see this creature, it’s no longer grazing, is it?

KALI HOLDER: Correct. Correct. By the time it comes to me, it’s no longer grazing.

IRA FLATOW: How did it die? Can you tell?

KALI HOLDER: Well, I could tell. So amphibians are super dependent on their kidneys. And so this gal’s kidneys were not doing great, and that was the cause of death there.

IRA FLATOW: You want to say a question?


IRA FLATOW: All right, let’s go to this question right here.

AUDIENCE: Hi. I’m Leo, and I wanted to ask, is it like something that– like a skill you gain over time? Like, when you started the job of doing surgery on dead animals–

KALI HOLDER: That’s a great description, I love it.

AUDIENCE: Like, did it start out as, aww, this animal died, I’m so sad, and it turned into, oh, I wonder what I could find in this?


AUDIENCE: A little bit?

KALI HOLDER: Yeah, no, that’s a great question. How did I end up here? I’ve always been weird. I’ve always been weird and I’ve always wanted to be a vet. So I am a veterinarian, but as I was coming up in the veterinary world, I found that the puzzles were really the things that got me. And so I do– I do nothing but solve puzzles all day.

And so how you end up being an anatomic pathologist? You start off kind of weird. You do vet school. And then you do three years of residency in just anatomic pathology, and then if you’re extra weird, you’re like, yeah, but what if we got the weirder animals? And then you do conservation pathology, which is how I ended up at the National Zoo. So I did extra schooling and training-type programs after my residency to work with the weirdest animals with the weirdest diseases so that I could take apart Caecilians and show y’all.

IRA FLATOW: Ah, weirdness. That’s our theme today. Let’s go on to another case–

KALI HOLDER: Yeah, let’s go to another case.

IRA FLATOW: This one is of the feline variety. Tell us about who this lion was.

KALI HOLDER: So this was Naba. She was a 19-year-old lioness, which is exactly as ancient as it sounds. Like she was very geriatric and had a wonderful long life at the zoo and was getting all kinds of supportive care for arthritis and renal insufficiency– the things that happen to old cats, right? Anybody who has an old cat, they know, they know. So she was an old cat.

And a year prior to her coming to me, she actually got COVID. And– because COVID doesn’t just affect humans, it can affect a variety of animals, and a lot of big cats at various different institutions got COVID. And our big cat house did have a COVID outbreak and she was one of the ones affected. And she came through beautifully–

IRA FLATOW: What’s the symptoms for an animal that has–

KALI HOLDER: It’s respiratory. So they were coughing– and that’s a scary sound, by the way, if you’ve– just as a primate, if you are around a lion when it goes, [COUGHS], you’re like, oh, Lord, I might die. Yeah, so there was that. And there’s some snot. They get respiratory disease. Some of them were asymptomatic, just like with humans.

So she came through the respiratory disease well. And six months later, she started having problems chewing. So her keepers were like, oh, it might just be dental disease. She was doing OK in terms of being able to eat, but she was eating oddly.

IRA FLATOW: Right. So she dies and you–

KALI HOLDER: She dies six months after that, but also, old animals were always concerned about cancer. And in her, I did actually find a tumor in her gastrointestinal tract that was causing an obstruction to bind there. So that invasion is what lets me know it’s absolutely cancer.

IRA FLATOW: And you were saying that she had a little bit of a funny movement in her face–

KALI HOLDER: Yeah, so she had a funny movement in her face, and–

IRA FLATOW: This explains it?

KALI HOLDER: This does not explain it. I did not– I was like, hmm, that doesn’t explain it. So we took open her skull and this is her brain. So the whole back part of her cerebrum is open. It should not be, and it probably was not that way for most of her life. This probably happened about six months ago when she started having problems chewing. That area does a lot of the coordination for facial and trigeminal nerves and things like that that are going to help organize how you move your tongue and chew.

And so her chewing being abnormal was actually a neurologic sign from this giant hole in her brain. So what happened here is the blood was obstructed, and then that center part just died.

IRA FLATOW: She sort of had a heart attack in her brain?

KALI HOLDER: She had a stroke.

IRA FLATOW: A stroke?

KALI HOLDER: This is stroke. Yeah. So this is a stroke for sure. 100%. I can tell you this was a stroke. Why she had a stroke? Well, she’s old, she’s got kidney disease, those are two predisposing factors. But she also had COVID. And COVID does predispose to strokes in humans. And some of the research that has been done on it, the stroke size associated with– stroke lesion size associated with COVID has been shown to be larger. And that was a huge area. That would be like a territorial infarct is how I would describe that.

IRA FLATOW: So she had multiple problems?

KALI HOLDER: Oh yeah. Oh yeah.

IRA FLATOW: Right? She had COVID.

KALI HOLDER: She had COVID. And then she had cancer. And she also had renal disease. She was still doing OK on that, but the big problem was the cancer. It doesn’t take a lot of brain to run a lion, actually. It really doesn’t. Or my cat, honestly. You look at him, it’s just no thoughts, only vibes.

IRA FLATOW: There you have it.

KALI HOLDER: But yeah. She doesn’t have to– she doesn’t have to compete for food. And even if she had visual deficits, cats are really great at navigating places. We have a blind cat at home and she does great navigating. So even if she had visual deficits, the fact that she was in a familiar environment, she was she was doing pretty well with her quality of life, yeah.

IRA FLATOW: Yeah, yeah. Let’s go to the audience. Question here.

AUDIENCE: So I want to be like something in forensics when I grow up, or something in surgery. And I was just wondering, like, have you ever had that moment when you’re doing, I don’t know, you’re like daily cutting up of animals that you’ve, like, opened an animal and you’ve been like, oh, that should not be there? Or, like–

KALI HOLDER: Oh yeah, yeah, yeah.


I love those. I love when I can open up an animal and it’s immediately apparent what happened. Sometime– this is one of my favorite. So this is kind of a gross one. I opened up a beaver, and immediately the smell told me exactly what had happened. Because the beaver smelled like the inside of a horse whose stomach had ruptured, and what had happened was the beaver’s stomach had also ruptured and it smelled exactly the same. I was like, oh, I know that smell. That is the smell of gastric rupture in an animal that cannot vomit.

So horses and beavers both have very tight sphincters at the top of their stomachs, so if anything starts producing gas in there, it can cause a burst. And so that beaver not only had gas-producing bacteria, but also had a bacterial infection in the wall that was weakening it, and it busted through. And I could tell by just opening up and smelling, yeah. That’s when you know you’ve made it.

IRA FLATOW: I think we’re ready for a TV show.


IRA FLATOW: All right. Thank you.

KALI HOLDER: All right, thank you!

IRA FLATOW: Kali Holder, veterinary pathologist at Smithsonian’s National Zoo and Conservation Biology Institute here in DC.

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