Fleas!

Dr. Michael Kent speaks with Dr. Erin Lashnits on fleas and how they affect our dogs and cats. 

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The Vetrospective Podcast Season 01 Episode 01
Dr. Michael Kent with Dr. Erin Lashnitz
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DR. LASHNITS: It's probably way more about flea biology than you really want to know.
DR. KENT: No, actually, this is fascinating for me. Hopefully everyone else is enjoying learning
about this too, but it's more than I learned in vet school.
Hello, this is Michael Kent. I'm a professor in radiation oncology at UC Davis, and welcome to
today's episode of Vetrospective. Fleas. When I think of fleas, I think of these common insects
that are also parasites and really are a nuisance. They bite and feed on our dogs’ and cats'
blood, which can cause itching, hair loss, and result in hot spots. The itching is annoying and
affects their quality of life. In severe infestations in small dogs and cats, in particular, you can
wind up with anemia or blood loss anemia. Fleas will also sometimes bite people, and this can
transmit disease. So I'm here today with Dr. Erin Lashnitz, and we're going to talk to you about
this some more. So welcome and thank you for joining me, Erin.
DR. LASHNITS: Hi, yeah, thanks for having me.
DR. KENT: So just a little bit of an intro on Dr. Lashnitz here. She did her undergraduate work
and master's degrees in biological sciences at Stanford. She then went on to Cornell University
for veterinary studies, where she got her DVM degree. And then did an internship in private
practice in Brooklyn. Is that right?
DR. LASHNITS: Yep. Yeah.
DR. KENT: And then after completing her internship, she went on to do a residency in small
animal internal medicine and her PhD in comparative biomedical sciences at North Carolina
State. It's all very impressive. So after completing her studies, she went and joined the faculty
as a clinical assistant professor at the veterinary school at the University of Wisconsin. She has
over 25 publications in print now and is known for her work in flea-transmitted diseases. So
again, welcome, Dr. Lasnitz, and thank you for joining us.
So I'm always curious, I wanted to start out by just asking, why and how did you get into
veterinary medicine? You know, why choose VetMed.
DR. LASHNITS: Yeah, good question to start out. I was not one of the kids that wanted to be a
vet from the time I was five years old, like my daughter is currently.
DR. KENT: Excellent.
DR. LASHNITS: I wasn't sure what I wanted to do, like as a kid or teenager or even in college,
really. I wanted to do science, but I didn't really know what that meant. So after I graduated, I
got my master's because I sort of didn't know what I wanted to do. And after I graduated, I was
working in a lab at UCSF, actually, doing sort of cancer research, cancer biology, and we worked
with a mouse model.
DR. KENT: A woman after my own heart doing cancer work.
DR. LASHNITS: That's exactly right. Yeah. I was more on the chronic inflammation side. We
were studying angiogenesis.
DR. KENT: Fair enough. So angiogenesis meaning new blood vessel growth.
DR. LASHNITS: Yes, yeah, It was a cancer research lab. We were just doing sort of the
angiogenesis work. But anyway, I was working with mice, helping to sort of take care of the
mouse colony where they were doing testing of various different kinds. And I really liked
working with mice. And I sort of had this existential, like, I like working with mice, but I really
wish that I could help them instead of just using them for research. Like, what if I could help
animals? And wouldn't it be cool to be a doctor? But I don't really want to be a doctor for
people. But what if there was a job, like you could be a doctor for animals? And I spent
probably like six months just wondering about that before it came to me, like, oh, right, there is
a job like that. It's a veterinarian; like most kindergartners know about it.
DR. KENT: Yes. It just took you a little bit longer to find it.
DR. LASHNITS: Yeah, it took me a little longer. And so, then I started sort of doing my pre-reqs
and working at the San Francisco SPCA and getting all that kind of stuff under my belt and just
getting a little bit more experience in the actual vet world. It's like post-college.
DR. KENT: Yeah, so then you became a vet and then you went, I want to be an internal
medicine specialist. How did that grab you and what led you to kind of where you are now?
DR. LASHNITS: Yeah, so, having taken sort of a little bit of a winding path to get to vet med in
the 1st place, when I came into vet school, I thought I wanted to be a wildlife or conservation
type of vet, maybe work at a zoo. So I spent my whole vet school preparing to go do a residency
in zoo med. I was really interested in ecology and wildlife and stuff like that. And so I got to my
clinical rotations in 3rd and 4th year and spent a couple of rotations at a couple of different
zoos and realized that I didn't really like it. Intellectually, it just wasn't really my jam. Like we
would do some blood work on a species and then kind of be like, well, this is the first time
we've ever looked at blood work on this species. So I wonder if it's normal. We don't know if it's
normal or not, right?
DR. KENT: And is there a disease? We don't know. Yeah.
DR. LASHNITS: So that was tough. And sort of in contrast, then I spent just two weeks on
internal medicine, small animal internal medicine in the hospital at Cornell during my 4th year,
and I loved it. I just, it was like the exact opposite, right? We spent like hours talking about the
blood work on every single patient. And I was like, wow, you could really delve into this. Like,
we can really find out what's wrong with these pets. We can help them. And so that really kind
of scratched that intellectual itch for me. But I didn't go right into like internship residency
straight away. I didn't really know what I wanted to do, but I sort of knew I wanted to maintain
a research lab of some kind and maybe go back into academia eventually, because that's where
I had sort of come from this idea of maybe I would do a PhD. And so I ended up doing private
practice and ER and GP for a couple of years after my internship actually and then applying for
internship and for a residency and PhD at NC State.
DR. KENT: So then after that, you went to Wisconsin. And so why academia? Why are you
staying in academia? Why at the golden palace and not in a private practice? What drives you
to be here?
DR. LASHNITS: I actually really liked my time in GP. I spent 2 1/2 years or so as a general
practice vet. I really liked seeing sick patients, but like we had, you know, we had sort of urgent
care and that kind of thing and it was really fun. It was sort of, interesting to be the first
opinion, right? Like somebody would come in with a cat who just like wasn't feeling great and
you had no idea. And the extra challenge was particularly for clients that didn't have a lot of
resources where you could just like, if you could just do a really good physical and like find the
thyroid slip or palpate some enlarged lymph nodes and give them like at least a tiny bit of an
answer or a direction that you could say, hey, we can spend not very much money and I can
probably tell you what's going on. And maybe how to approach it, how to treat it. So I really
liked that. But I also really like research. I really love teaching. I kind of wanted to be sort of
having had that experience, I wanted to be kind of more behind the scenes, like kind of
contributing to the development of veterinary medicine and veterinary students and curriculum
and that kind of thing for the long term. So yeah.
DR. KENT: So now I invited you here because we were teaching a class together. We were
teaching a lab on how to do bone marrows. And I was asking you, what your research interests
are because you're a fairly new faculty to Davis, right? And so this is how I'm transitioning us
back to fleas. And, you know, I know there's a dog flea and I know there's a cat flea and I had
this in vet school years ago. So can you just talk maybe a little bit about which is more common
on which species? Because it's interesting, right? And Just tell me a little bit more about these
real small, annoying creatures.
DR. LASHNITS: They are small and annoying. So what we learned in vet school was dog fleas
and cat fleas. And it turns out that actually, like we used to think these are two different
species, right? So Ctenocephalides canis, dog flea. Ctenocephalides felis, cat flea. But it turns
out that actually probably a lot of them are just C. felis. So when you say anatomy.
DR. KENT: C Felis, what we're doing is we're abbreviating because that's so hard to say.
DR. LASHNITS: Yes, exactly. Nobody wants to have to say Ctenocephaladis felis us over and
over again.
DR. KENT: I don't think I can say that once, much less 10 times.
DR. LASHNITS: Yeah, so in general, most of the time when you see a dog with fleas, that dog
actually has cat fleas.
DR. KENT: Got it.
DR. LASHNITS: Not dog fleas.
DR. KENT: Thank you.
DR. LASHNITS: And then so also the cat flea, like it's not just for cats, right? It's not just for cats
and dogs. It has a huge range of different species that it will jump on, including people. And so
it's an interesting sort of thing about the biology of this flea as opposed to some other fleas that
are very species specific.
DR. KENT: So it's not like, I know lice are very species specific, right? Like we don't catch pigeon
lice, which if you've ever seen them, they're huge.
DR. LASHNITS: Yeah.
DR. KENT: Kind of scary looking. But so fleas can actually cross species.
DR. LASHNITS: Yes, fleas cross species a lot. So if you have cats and dogs in your home, if a cat
has fleas, the dog will get fleas and vice versa. And they're the same fleas. They're all going to
be C. felis.
DR. KENT: Okay.
DR. LASHNITS: And the ones that bite you are also going to be C. felis.
DR. KENT: So can you tell me about their life cycle a little bit? You know, it's been years since
I've looked at this. I know there's larval stages, there's adults, and then they need certain, like, I
don't know even what the words are, but we basically need to have certain conditions so that
they can complete their life cycle. And maybe we can bring a little more understanding to this.
DR. LASHNITS: Yeah, So there is a life cycle. Basically, the females lay eggs. The eggs hatch into
larva. The larva exist as these like little teeny motile like tiny microscopic wormy things.
DR. KENT: And are they on your dog or your cat or are they in your carpet?
DR. LASHNITS: They are in your carpet. The eggs fall off of the dog or cat into the carpet and
anywhere else. The pillow, the couch, the bed, your bedding, wherever the animals. And then
the eggs hatch, and then the larva. So the larvae hatch from the eggs. The larvae actually eat
the flea feces, which we would call flea dirt because it's gross to call it flea feces, but that's
what it is. It's just flea poop. So flea dirt is actually flea poop.
DR. KENT: And flea poop is mostly what?
DR. LASHNITS: Flea poop is mostly the blood of whatever the flea was feeding on.
DR. KENT: So the larvae eats your digested dog or cat's blood.
DR. LASHNITS: Exactly.
DR. KENT: They really are parasites.
DR. LASHNITS: Yeah, they're really gross. So the larvae feeds on the flea dirt. And then it forms
a cocoon and it pupates. And that is what can persist in the environment for a really long time.
DR. KENT: Like a week or months or a year.
DR. LASHNITS: I've heard stories of potentially like a year, but definitely at least six months or
so. And then it will hatch out of that cocoon into the adult flea, like the flea that we know, you
know, what it looks like.
DR. KENT: What we can see?
DR. LASHNITS: Yeah, the thing that we are familiar with. It'll hatch, depending on the
conditions, it can hatch as quickly as about two weeks. if it's like the prime temperature and
humidity and all of that. But it can also last for a really long time. So it can last six months or so
in the environment, even up to a year, maybe longer. And what it will do is it will wait basically
for a host to come by. The way it senses that probably has to do with like lights and shadows
and maybe carbon dioxide. But basically, it'll wait for a new host, and then it'll hatch out into
the adult, because if the adult doesn't start feeding right away on blood, it won't survive.
DR. KENT: It won't survive. It needs to have a meal, a blood meal, pretty quickly. Exactly. So
basically, the egg is going to release the adult, and that... needs to get a blood meal pretty
quickly.
DR. LASHNITS: Yeah. And this is the reason that the life cycle is important in a lot of ways is
because the length of it is determined by environmental conditions, but it can undergo the
whole life cycle inside. And so this can just live in your house, right? And your house is pretty
environmentally controlled, especially in the range that fleas like, which is like 50 degrees
Fahrenheit up to maybe like 100 degrees Fahrenheit. So wide temperature range. Usually your
house is within that, hopefully, yes, hopefully. And kind of range of humidity, but likes more
humid climates. But this is the thing that people will talk about is like when you rent a new
apartment, for example, it may have been empty for a few months, but if the last people had
fleas, those eggs, or sorry, those pupae are waiting in the carpet, sort of waiting for new hosts
to come by for them to hatch and jump onto your dog. And so I'm very paranoid about it now.
So I don't like to rent anything with carpet. But I understand it happens. But that's where that
life cycle is really important to understand and like why we'll always make sure that we have
our pets on their preventatives when we go into like an Airbnb or a hotel or anything like that.
DR. KENT: Yeah, because you don't want those fleas, which fed off another animal's blood, to
then jump onto yours. We're going to talk a little bit more about that later when we get into
some of the other diseases. But I wanted to jump to the first disease that I always think of.
Well, we think of the itch, we think of the bite, we think of that and flea allergy dermatitis and
controlling that. But really, you know, that's a symptom in a sense. What about tapeworms? So
that's probably the one I think of most. And I know dogs can get tapeworms from fleas. So can
you explain a little bit about this? So how do you know if your dog has tapeworms? Do they
cause clinical problems? Should we treat infections? And how do we treat them?
DR. LASHNITS: Yeah, so dogs and cats can both get tapeworms from fleas. There's a ton of
different tapeworm species. But there is one that's carried by cat fleas. And interestingly, the
way that the dog gets, or cat, gets tapeworms from the flea is they have to eat the flea. So it's
not spread by the actual flea biting.
DR. KENT: So it's when they're chewing because they're itchy, or cat would be grooming
because their skin is itchy, that they're going to actually ingest an adult flea and the tapeworm
is in that adult flea.
DR. LASHNITS: Exactly. And then it sets up infection in the dog's or cat's intestines. And then
eventually that infection will become patent and the dog or cat will poop out the little
proglottids, which are the little segments that look like grains of rice that hopefully you have
never seen in your own pets, but maybe you have.
DR. KENT: Maybe.
DR. LASHNITS: But definitely most people have seen in some form or at least pictured on the
internet.
DR. KENT: Yes, and if not, you can Google it and make sure safe search is on.
DR. LASHNITS: But generally, they don't cause, unless that's very young puppies and kittens,
generally in adult animals, it doesn't cause really severe infections.
DR. KENT: But it is a signal that you actually have fleas. So if you have tapeworms in your pet,
that means they have fleas.
DR. LASHNITS: That's right. If you have tapeworms, you have fleas. Which is, in my mind, more
concerning because in baby puppies and kittens, you can get a big enough burden that it can
really make them sick. They can get impactions and stuff like that.
DR. KENT: Impaction meaning, meaning like it can actually fill up their intestines to the point
where it gets like a blockage. Yeah. So that's going to be obviously dangerous and life-
threatening. But for an adult, it's usually subclinical, meaning they don't, they're not going to
get too sick from it, right?
DR. LASHNITS: Yeah, maybe like a little diarrhea, maybe a little bit of like irritation back there.
but generally not too sick from it.
DR. KENT: And normally when you go to the vet, because you want to check for parasites, you
usually do something called like a fecal smear or fecal flotation, and they'll look for them. Do
they usually find the tapeworms then, or is it more that you've got to look for those grains or
rice?
DR. LASHNITS: Yeah, it's a good question. There's actually been a lot of research done more
recently on like how do we actually diagnose tapeworms and are they being underdiagnosed
because your typical fecal float that your vet would regularly do to check for other parasites is
not very good at picking up tapeworms. And so a lot of the time... And I saw this when I was out
in general practice. We would have patients coming in because people saw the segments in the
feces.
DR. KENT: And not everyone looks at their dog's poop. Hopefully if they're out walking their
dog, they're picking it up, being good, responsible pet owners. But in your cat, you may not
notice it either, right? Unless you see it in the litter box. But mixed with the litter, it may be
hard to see.
DR. LASHNITS: So some of the companies have now developed more sensitive screening tests
and they're showing that maybe even higher numbers of cats and dogs carry tapeworms than
they previously thought using like PCR and stuff like that. So if it's something that you're
worried about, it is now easier to test for. But also we know that like if you can clear the fleas,
then you can help clear the tapeworms. And if you don't clear the fleas, then it doesn't matter
how much deworming you do, the tapeworms are coming back.
DR. KENT: So and then our standard treatments for tapeworms, prevention, and then I know
there's something called droncit that we use, right.
DR. LASHNITS: Yeah.
DR. KENT: But now is it, it's more a matter of treating the infestation than actually worrying
about the tapeworms themselves.
DR. LASHNITS: Yeah, I think similar to how we think about some of the things on like a 4DX
snap test being a signal that like your dog gets bit. 4DX snap test is a test that looks at four
different vector-borne diseases. Three of those are tick-borne diseases.
DR. KENT: So vector-borne meaning that the animals, our dogs, our cats can catch them from
getting bit by a flea or a tick and it transmits disease.
DR. LASHNITS: Yeah, exactly. So like things that are transmitted by sort of insects that bite. And
we think about that's like a blood test that we would do as a screening test for your cat or dog.
And sometimes that result is more a signal that, hey, you have exposure to ticks here, as
opposed to something that, oh my gosh, we have to treat this disease right now. So I think of
tapeworms sort of like that, as if you're seeing tapeworms, yeah, we should do some
deworming and make sure that those are covered. But also it's a signal to me that you have a
flea infestation and probably need to think about that.
DR. KENT: So yeah, well, the tapeworms gross, having the fleas can actually be pretty gross and
more of a problem, too. Yeah, right. So, what other infections can dogs and cats get from flea
bites? So, why do we worry about it if we have... some itching, which is annoying, and we have
some tapeworms, which really aren't that big of a clinical problem, even if we really don't want
to see them. But why is this an interesting parasite? What else can they cause for dogs and
cats?
DR. LASHNITS: Yeah, so this is actually where most of my research falls, is trying to figure out
really what all things fleas carry and can transmit, and what things that are, what diseases that
are relevant to dogs and cats and people cat fleas carry and transmit. Because you can imagine,
you can test cat fleas for different types of bacteria or pathogens. And sometimes you'll find
those in the cat flea because the cat had it, right? So because the cat flea drinks cat blood,
sometimes there's just some pathogens in the flea because of the blood inside the flea. But that
doesn't mean the flea is necessarily able to transmit it to the next cat or dog or person that it
bites.
DR. KENT: So does a flea bite one dog or one cat in its lifetime? Or does it jump on and off and
maybe go between your pets? Maybe goes from your cat to your dog? I have a dog and two
cats.
DR. LASHNITS: Yeah. So the sort of conventional wisdom is that once a flea, it like jumps onto a
host, it pretty much stays on that host because there's a lot of blood inside that host and it
doesn't really need to leave. That can change with probably like the density of infection. Like if
you have a so, many fleas, some of them will just be jumping off looking for a better home.
DR. KENT: The little kitten that's brought into the hospital that has 1000 fleas on it and it's so
anemic, it's gonna die if we don't get those fleas off it. That's what you're talking about. Yeah.
DR. LASHNITS: And then also they seem to respond to like temperature. And so I don't know if
you've experienced this, but a lot of vets have experienced when you anesthetize those
animals.
DR. KENT: Yes, definitely.
DR. LASHNITS: And whether it's a reaction to the anesthesia or the patient getting cooler, but
when you anesthetize for like a spay or a neuter, the fleas will start to jump off.
DR. KENT: Yep, they're abandoning ship. They think this is not a good host anymore.
DR. LASHNITS: So that can probably happen too. And that's when they would jump onto
whoever is nearby and try to find a new host. And then another question that is sort of an open
question in flea biology and disease transmission is whether fleas can pass pathogens from the
adult flea to the egg.
DR. KENT: And then the pupa and then the next.
DR. LASHNITS: And the larva and the pupa. And so interestingly, the larva that eats the flea dirt,
eats the flea poop, right? That flea poop is the animal's blood digested through the flea. And so
that's one of the theories as to how fleas might maintain infection throughout their life cycle is
not so much that the mom flea passes it to the flea egg, but rather the mom flea is infected
with whatever pathogen it is. And then as the larva drinks or eats the flea poop, that's how it
gets infection through the life cycle.
DR. KENT: Interesting. It's a kind of unique pathway that we don't see a lot in nature, right?
DR. LASHNITS: Yeah, it's very unique, and actually, fleas are particularly unique. It's probably
way more about flea biology than you really want to know.
DR. KENT: No, actually, this is fascinating for me. Hopefully everyone else is enjoying learning
about this too, but you know, it's more that I learned in vet school.
DR. LASHNITS: Fleas are different from a lot of other blood sucking parasites because they're
such constant feeders. So if you think about a tick, a tick will feed maybe like three times in its
whole life.
DR. KENT: Yeah, it engorges and gets really big. Everyone's seen that engorged tick before.
DR. LASHNITS: Yep, and that's done and it molts and it goes to a different life stage. But fleas,
they will feed, they will bite and they'll drink some blood and they'll bite again and drink some
blood and its sort of constant and they're constantly drinking blood and pooping and drinking
and pooping.
DR. KENT: Which is why we see so much flea dirt on our pets. Or if you've ever bathed an
animal who has a lot of fleas and literally the flea poop or the dirt looks like blood again when it
rehydrates.
DR. LASHNITS: But that's one of the things that helps the flea sort of maintain, it's like one of
the things that contributes to flea immunity. So the flea not getting infected is that there is such
a like flow of blood through the GI tract. And so pathogens that are transmitted by fleas have to
have developed a way to stay inside the flea despite this constant feeding, which is why some
of them have developed the potential to make biofilms, which contributes to disease within.
DR. KENT: So a biofilm, will you explain what that is?
DR. LASHNITS: Yeah, oh gosh, I'm probably not the person to explain biofilms, but essentially
what it is like instead of bacteria sort of floating free in solution, they make like a little film of
almost like what you could think of as like algae.
DR. KENT: So almost its own environment.
DR. LASHNITS: Yeah. And so they can do that sort of on the epithelial walls of the gut of the
flea. And so then it doesn't, the bacteria wouldn't get like excreted out right away as the blood
is flowing through the GI tract of the flea.
DR. KENT: So now I ran you down a rabbit hole, but really I was wondering like what other
infections can dogs and cats get from fleas.
DR. LASHNITS: Yeah. So major tangent.
DR. KENT: I'm really good at that.
DR. LASHNITS: That's okay. So the biggest infection that we think about as flea born is
Bartonella. Bartonella henselae being the main one.
DR. KENT: And that's a type of bacteria, right?
DR. LASHNITS: That is a type of bacteria. It's cat scratch disease or for those of us that are of
the right age, cat scratch fever, which they did rename for the medical version because of the
Ted Nugit song.
DR. KENT: Yes, I was going to say because of the song.
DR. LASHNITS: You can get the sound, the sound folks to put in cat scratch fever in the
background.
DR. KENT: Maybe, but I don't know. We probably would have to.
DR. LASHNITS: Can't afford it.
DR. KENT: No, we have no budget.
DR. LASHNITS: For the $0.
DR. KENT: Zero dollars. Standard veterinary medicine.
DR. LASHNITS: Yeah. So yeah, cat scratch disease, which is Bartonella henselae, is sort of
canonically, sort of prototypically transmitted by cat fleas.
DR. KENT: So it's not actually the cat scratching you, but if they scratch you and they have had
fleas that can transmit it, how does that work?
DR. LASHNITS: Exactly. So the reservoir host is the cat. So the Bartonella henselae lives in the
cats, usually bloodstream. But it's not very often that the cat's blood would mix with your blood
other than in situations where the cat's blood is being sort of taken out of its body by the fleas,
right? And so in a cat with fleas, there's all this flea dirt around. And the flea dirt is actually...
DR. KENT: So there's partially digested cat blood basically sitting on the surface of the cat.
DR. LASHNITS: And so it's infected. Yeah. So this cat's scratching all the flea bites that it has.
And then if you get scratched by that same cat, it inoculates the infectious.
DR. KENT: So it's almost like a vaccine of the badness. You know, it's basically a needle. You've
seen sharp cat nails before. And so they can just inject the…
DR. LASHNITS: Yep.
DR. KENT: So now everyone wants to treat their flea, their cats, because you don't want flea
poop made of your cat's digested blood getting injected into you.
DR. LASHNITS: Exactly.
DR. KENT: So and then what does it cause in people? So this is actually a one health issue. This
is a zoonotic infection and zoonotic infection means something that can be transmitted from an
animal to a human. So this sounds important. So What does it cause in people?
DR. LASHNITS: Yeah. So cat scratch disease is really a disease of people. It was discovered in like
the 1990s or so, mainly because of the HIV epidemic.
DR. KENT: So immunocompromised people where infections are worse.
DR. LASHNITS: Exactly. It was much more common to see systemic manifestations of Bartonella
henselae infection in people with HIV that were immunocompromised.
DR. KENT: That's why for a while, human physicians were telling people to get rid of their pets,
even though they were so important. for your well-being and maintaining your quality of life
and that you have these connections while you're going through such a horrible disease that
they're saying you can't have your pet anymore.
DR. LASHNITS: Yeah. And at that time, we didn't really understand that it was flea born
necessarily. And so there wasn't, yeah, so they're like, really, all you have to do is make sure
that you don't have fleas on your cat. Your cat's fine, as long as you're not sort of taking blood
out of your cat and putting it into your own arm. Yeah, or get rid of the fleas so they're not
infected with this anyway.
DR. KENT: So what disease does it actually cause in people?
DR. LASHNITS: So in immunocompetent people, often it is sort of a self-limiting febrile illness,
meaning you get a little bit kind of just general sick, right? I don't feel that good. I have a fever,
maybe big lymph nodes, and those would be lymph nodes.
DR. KENT: Kind of flu-like.
DR. LASHNITS: Kind of flu-like. Usually not super respiratory, so you're not going to get like a
stuffy nose, cough, that kind of thing, but just like that, like, I can't get out of bed and large
lymph nodes where usually near where the inoculation was, right? So if you got scratched on
the arm, it might be the lymph nodes in your armpit that get big, that kind of thing.
DR. KENT: Got it. And then they'll go down after time. You're going to clear this.
DR. LASHNITS: Yep. And in a lot of people, it goes away on its own. In a lot of people, you get
treated with antibiotics and that helps it go away faster.
DR. KENT: Yeah, you feel a big lymph node, you see the scratch, you go to your. I was going to
say your vet, but you go to your physician. Go to your vet, go to your physician, and they're
going to treat you for it.
DR. LASHNITS: Yeah. But then there is a small subset of people, even people that don't have
existing immunocompromise or aren't on medications that change their immune system or
anything like that, where they can either get chronic infection or they can get these more
atypical manifestations. And that can look like lots of different things.
DR. KENT: So hard to diagnose.
DR. LASHNITS: Very hard to diagnose. It can, the main thing that we're worried about is there's
reports of it causing neurological illness. And then it can cause…
DR. KENT: Neurological illness like mental health issues or schizophrenia or seizures.
DR. LASHNITS: I know there's all. really in the very early stages of knowing what kind of things
we might actually see, but definitely sort of like meningitis, encephalitis has been reported.
DR. KENT: So swelling of the covering of your brain, swelling of your brain. Now, I don't want to
scare people because we don't want people getting rid of their cats. Again, you said we just
need to treat the fleas to make sure you can't get this. So What about, I know there's also
rickettsial diseases, rickettsial bacteria diseases. I think that's something else that we know not
enough about.
DR. LASHNITS: Yeah, definitely. So there is a flea-borne rickettsia. Rickettsia is the type of
bacteria that causes typhus, which is not something we think about very commonly in the US.
DR. KENT: Kind of like plague, which I know we occasionally come up with, but that's flea
transmitted as well.
DR. LASHNITS: Plague is definitely flea transmitted.
DR. KENT: We'll get to that in a minute.
DR. LASHNITS: We'll put it in plague. There's so many. So yeah, so typhus is caused by a
Rickettsia species, but there's also another one that is spread by cat fleas specifically, which is
called Rickettsia felis. We just don't know very much. Yeah, felis for cats, yeah. We just don't
know very much about it. It's been reported to cause similar sort of like febrile illness. but kind
of non-specific and really only recognized over the past maybe 5 or 10 years with PCR.
DR. KENT: So something we need to do a lot more work. So PCR being a diagnostic test we use
to basically identify things.
DR. LASHNITS: Yeah.
DR. KENT: And then, so we need more research in this area.
DR. LASHNITS: Yeah, definitely. I think one of the big open questions is in terms of any of the
pathogens or any of the diseases that fleas carry is are they carrying them but can't transmit
them? Or are they carrying them and can transmit them? Like we know for Bartonella henselae,
they're carrying them and they can transmit them.
DR. KENT: Yeah. Like your cat scratch disease that you were talking about. Exactly.
DR. LASHNITS: Yep. And then are there things that are less common? Because Bartonella
henselei, very common in fleas. Even Rickettsia felis, some of the other flea-born Rickettsia, is
very common in fleas. But are there things that are less common where maybe it only crops up
in certain geographic areas? or certain climates where we don't see it like spread across the
whole United States, but maybe only in certain areas where fleas are causing transmission of
certain bacteria.
DR. KENT: From animals to a human they happen to bite.
DR. LASHNITS: Yeah, because again, we know that the cat flea is an indiscriminate biter. It's
going to bite anything it jumps on. And so if it jumps on a cat and a person, it'll bite everybody.
And if it jumps on wildlife, it can be a source of transmission to wildlife, not just to the cats and
dogs that it bites, but also potentially to them.
DR. KENT: So in our free-ranging cats, our community cats, our feral cats, whatever you'd like to
call them, is this a bigger problem because there's not flea control?
DR. LASHNITS: Yeah, definitely. I would say so. And that's the population of cats that we've
mostly studied in my lab is free-roaming cats, right? Cats, whether they're owned or unowned,
but that have essentially like free access to roam where they want and often limited access to
veterinary care, meaning they're almost never on flea preventatives and definitely not year
round. And maybe sometimes they'll get one here or there when the flea burden is really high
or something like that.
DR. KENT: So how do you study that if they're free roaming, if they're out there in the wild and
they're not coming in for veterinary care? Like how do you go about that? Or how do you want
to approach this problem?
DR. LASHNITS: Yeah, it's a tough nut to crack, really. So I've had really nice success with working
with some of the trap, neuter, return organizations. So these are nonprofits that basically are
dedicated to improving the lives of these free-roaming cats by giving them at least a little bit of
access to veterinary care and often also by spaying and neutering them.
DR. KENT: Trap, neuter, release.
DR. LASHNITS: Exactly, trap, neuter, release. So they know that if they just remove cats from
where they're living, new cats will come in and live there. There's plenty of cats in the world.
And so they'll keep these sort of stable colonies and sometimes vaccinate them for rabies, try
to spay and neuter a large majority of them so the populations don't skyrocket. So we limit the
sort of the ecological downstream effects of these cat populations and essentially help them
live better lives. But then where I come in is that when they get trapped and neutered, we can
comb them for fleas and look at what fleas they're carrying, how commonly they're carrying
those fleas, and…
DR. KENT: What pathogens are in the fleas. What's your plans to expand your research in the
future? What do you want to do?
DR. LASHNITS: Yeah, well, as you said at the beginning, I'm new here to Davis.
DR. KENT: Welcome, we're glad to have you.
DR. LASHNITS: So I was previously at University of Wisconsin. We were working on trying to
sample fleas from all continental United States. This is like sort of a really basic epidemiology
problem in that we don't even really know how common fleas are amongst cats or dogs that
don't go to the vet across the whole country. And so really just trying to define sort of like, are
there places in the country where we really don't have fleas? Because you'll hear that, oh, we
don't have fleas here.
DR. KENT: I've had people tell me that and then I see the fleas on their animals.
DR. LASHNITS: Yeah, exactly. So trying to define if there are really places where it is just too
dry, essentially, for fleas. But we also know that fleas can maintain their entire life cycle
indoors. And so pretty much wherever there are people with pets, there are going to be fleas.
But we're also trying to kind of map and figure out the burden of disease for these different
diseases that the fleas carry across the country. Previously, I've been doing this working with
these community organizations like Trap, Neuter, Return and different shelters and that kind of
thing. And in the future, I'm really hoping to expand that to more of a citizen science type of
project because the cats that even the cats that come into trap, neuter, return are seeing the
vet a little bit, right? And the place where I'm really interested in looking is places where we
really don't even have any veterinary care or for owners that don't have the opportunity to take
their pets, right? They're not necessarily free-roaming cats, they're owned cats, but they may
not be on regular fleet preventatives and looking at the potential for disease and zoonotic
disease in those pets.
DR. KENT: So what are the clinical implications of, say, a Bartonella infection in a cat. Does a cat
become ill from that?
DR. LASHNITS: Yeah. Does a cat become ill from Bartonella? So what a good question.
DR. KENT: Or a dog.
DR. LASHNITS: Yeah, or a dog. So in fact, this is one of the things where I can't lump cats and
dogs together. So starting with cats. So cats are the reservoir species for Bartonella henselae.
Bartonella henselae is one species of Bartonella that's sort of bigger type of bacteria.
DR. KENT: So we've got one group of bacteria and you can have different types of bacteria
within that group.
DR. LASHNITS: Exactly. There is over 40 species of Bartonella that have been discovered now
since the 90s or so when we started figuring this stuff out. And so probably more than one use
cats as a reservoir, but you know, not all 40. And so there can be infections in cats that are not
with Bartonella henselei, right, that are with other species that are meant to be in, say, a dog or
a cow or a goat, and then they infect the cat, and that can make them sick. We also know that
there are species of Bartonella that have the reservoir in people. And that actually does make
people sick. Those are not zoonotic ones. They're just like transmitted person to person.
DR. KENT: There ours.
DR. LASHNITS: Yeah. But they make people sick. And so, because we know that, we can also
guess that the species that are sort of native to cats also sometimes make the cat sick.
DR. KENT: And again, flu-like.
DR. LASHNITS: Various different things. Definitely can be fever, can be sort of associated with
the immune mediated diseases that we think about, like anemia or low platelet count or things
like that. In cats, it's a little bit hard to define because so many of them just carry it without any
symptoms.
DR. KENT: And we don't know yet.
DR. LASHNITS: And we don't know. Dogs is a different story. So in dogs, the main manifestation
that we see with Bartonella infection is infection of the heart valves. So something called
endocarditis.
DR. KENT: And so that was going to cause a murmur then because the blood flow changes.
DR. LASHNITS: Yeah, And it's Bartonella, various species of Bartonella are probably one of the
top causes of endocarditis in dogs. And so if you have a dog that has endocarditis, it's a good
chance that it could be Bartonella.
DR. KENT: So inflammation of the heart. “It is” always means inflammation, right? So, of the
heart valves.
DR. LASHNITS: Yeah.
DR. KENT: So you've convinced me over this last 30 minutes or so that fleas, you know, we
don't want to panic, but fleas, fleas can be dangerous. So What's the best way to protect our
dogs and cats from fleas?
DR. LASHNITS: Yeah. The happy news is that since the past maybe 20, 30 years, it's gotten way
easier. So there are tons and tons of products out there that are actually really, really effective
at preventing fleas and treating fleas. The thing is that you have to use them. And use them
regularly. And it kind of, so having no sort of corporate sponsorship whatsoever, to me, it
doesn't really matter what you use. There's a lot of less expensive options. There's a lot of very
expensive options. There's a lot in the middle. All of them are pretty effective as long as you use
them as you're supposed to. So if you're supposed to give it once a month, give it once a
month. If you're supposed to replace a collar after six months, replace it after six months. and
do that regularly. And we've done studies in using a lot of these different products to show that
we used to think you had to treat the environment, meaning like do like flea bombs for your
house, right?
DR. KENT: And vacuum.
DR. LASHNITS: And vacuum and go crazy with like all of these like pretty horrible chemicals for
your house. In fact, we probably don't need to do that as much as we used to think, but we do
need to treat our animals more sort of diligently.
DR. KENT: You break the life cycle, if you kill the flea, then it's not going to have the pupa
larvae.
DR. LASHNITS: Exactly.
DR. KENT: And a new adult.
DR. LASHNITS: And the fleas, the eggs will, the eggs and then the larva and then the pupa will
sit in the carpet, right? Or sit in your house or sit in the pet's bed. And they'll come out when
the pet is now not protected. And so if you can get them protected for months at a time, it does
break that life cycle.
DR. KENT: So you should treat year-round regardless of what it's like outside, because inside its
nice and warm.
DR. LASHNITS: Exactly.
DR. KENT: And let's say you are going to move into that apartment or the new house and
there's carpet down. Then should you treat the environment?
DR. LASHNITS: You know, it's a good question. I haven't. Really, and I don't think many people
do. I think that really the important thing in that situation is to make sure your pets are
protected before you get into that environment, right? So whether that's like doing the spot on
or putting the collar on or whatever it is, do it before you actually enter the environment. So
you just don't even have it as an option.
DR. KENT: There's no life cycle to happen then.
DR. LASHNITS: Yeah.
DR. KENT: This has been great. I really appreciate it. And one more question. Is there anything I
should have asked you? Was there something big I missed? I mean, I'm not a flea expert, and
now I feel like I'm more of one, but that's still…
DR. LASHNITS: No, but we should talk, go back and talk about plague.
DR. KENT: Plague, yes, we brought up earlier. Thank you. So I know plague happens even here
in California. It happens up in around Tahoe, the foothills, right? So plague is also transmitted
by fleas.
DR. LASHNITS: Plague is transmitted by fleas. Generally out in the environment, like the case in
Tahoe this year, that would probably not have been a cat flea. That's going to be wildlife and
wildlife flea cycle. But it can infect cat fleas and it regularly infects cats. Because cats interact
with wildlife in predatory ways, the thought is that basically the cats and or their fleas can get
infected and that's how the transmission can get back to people from these little like ground
squirrels or prairie dogs or whatever it is that's out in the environment that is the reservoir for
plague and this usually happens in the Four Corners or places like Yosemite, Tahoe, that kind of
thing.
DR. KENT: So this is not something, we don't want plague coming back. That was one of our old
pandemics, right? We don't want plague coming back. So another reason to treat our dogs and
cats and particularly cats who can come in contact with wildlife.
DR. LASHNITS: Yeah, and especially if you have outdoor cats in those places, it is actually really
important to keep them on monthly preventatives because if those cats bring back plague, like
you do not. I mean, we can treat it with antibiotics, but man, you don't want to get it.
DR. KENT: No. Something I don't want, that's on my list of things I don't want, is plague. We
learned that in the Middle Ages quite well as a species.
So, Erin, Dr. Lashnits, thank you so much for joining me today. It's been a lot of great
information. I really appreciate you taking the time for me and for our listeners. So we've taken
a deep dive into fleas and hopefully we've convinced you we should avoid them.
DR. LASHNITS: Thank you so much. Thank you.
DR. KENT: All right. The Vetrospective, as with life, takes a village. I want to thank those who
suggested I start this project and everyone who has encouraged and supported me along the
way. Particularly, I want to thank our producer and director, Danae Blythe-Unti, Nancy Bei, who
is our program coordinator, our sound mixer, Andy Cowitt, and theme music was composed
and produced by Tim Gahagan. Thank you all, and we'll see you next time.