Current Vet

In this episode of Current Vet, Dr. Lottie talks about feline chlamydiosis, what the top differentials are, how we can recognise clinical signs and what we should be doing to prevent spread.

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Timeline:
00:00 Intro
00:28 Case
02:26 Aetiology & Pathogenesis
04:54 Clinical Signs
06:35 Diagnosis
09:56 Treatment
15:02 Key Points
16:20 Outro

Recommended Reading

References

Current Vet is an educational podcast intended for veterinary students, veterinary professionals, and individuals with an interest in veterinary medicine.

All content provided in this podcast and its associated materials is for educational and informational purposes only. It is not intended as, and must not be considered a substitute for, professional veterinary advice, diagnosis, or treatment.

Any clinical cases discussed in this podcast are fictional, and are designed to reflect typical or likely clinical scenarios for educational purposes. They do not represent specific real-life cases, clients, or animals.

While every effort is made to ensure accuracy and alignment with current evidence at the time of publication, veterinary medicine is a rapidly evolving field, and recommendations may change over time.

Creators and Guests

Host
Dr. Lottie Wilkinson
Creator and host of the Current Vet podcast

What is Current Vet?

The podcast that makes veterinary medicine simple.

In each episode, Dr. Lottie breaks down clinical conditions, cases, and concepts across species, focusing on pathophysiology, decision-making, diagnostics, and what actually matters in practice. It’s the kind of context that makes your knowledge finally click.

Every month, we’ll also have honest conversations with guests about the incredible variety of veterinary medicine, what you can do with a vet degree and how to think bigger about your career.

Whether you’re cramming for exams or looking for a soundtrack for your dog walk, Current Vet will make veterinary medicine simple

Intro

[00:00:00]

Hello, hello, and welcome back to Current Vet. This is the podcast that makes veterinary medicine simple. I'm your host, Dr. Lotti, and today we're talking about a condition that is quite common in veterinary practice, especially in young cats. Those from rescue centers, those in multi cat households, and it is feline chlamydias.

Case

It is mid-morning in consults and you are already running an hour behind. Your next patient is Tiggy, a 1-year-old domestic shore hair who lives indoors with three other cats. Her owner, Dan places her carrier on the table and says that she's been squinting a little bit and her eye looks quite sore.

He thinks she might have scratched it. When you open the carrier, Tiggy is bright and alert, but a little bit nervous. You gently restrain her and examine the left [00:01:00] eye first.

Straight away you notice marked conjunctival hyperemia, chemosis, and a thick muco perent discharge in the medial canthus, which is starting to crust into her fur.

The cornea, however, looks quite clear and smooth. And when you later perform a fluorescein test, there is no uptake, so no indication of corneal ulcer. You ask Dan a couple more questions and he mentions that Tiggy had slightly watery eyes a few weeks ago, but it cleared up on his own and he thought it was just irritation from dust or maybe an allergy.
He also mentions that two of his other cats have had weepy eyes around the same time, but they got better. No problem. Tiggy is eating normally. There hasn't been any sneezing, no coughing, no nasal discharge, and no changes in behavior, you now pause and start building your differential list.

So unilateral [00:02:00] conjunctivitis, minimal systemic signs, a recurring pattern, and the fact that she lives in a multi catt household where other cats have shown some other signs. You are obviously gonna be leaning away from things like trauma or allergies and more towards an infectious cause, a couple of our top differentials are gonna be feline, herpes virus, calicivirus, mycoplasma, and chlamydia.

Aetiology & Pathogenesis

Feline chlamydias is caused by a bacterium called chlamydia felis. It is an obligate intracellular bacteria, which means that it can't survive or reproduce on its own in the environment.

It has to live inside host cells. This is what is gonna make the disease so persistent and frustrating to treat because it hides in the cells and it is able to evade the immune response. It is also [00:03:00] protected from a lot of antibiotics that don't penetrate into cells very effectively. The bacteria itself has a two stage lifecycle.

The infectious form called the elementary body attaches to epithelial cells in the conjunctiva and the upper respiratory tract, once inside the cell, it is gonna transform into what's called a reticulate body, which is the form that undergoes replication.

After replication, the bacteria convert back into elementary bodies are released from the cell, infect neighboring cells, or are shed into the environment via ocular and nasal secretions. So this whole process is basically resulting in cell damage, inflammation, , and that is gonna cause the conjunctivitis that we see .

Because the bacteria mainly stay in the conjunctiva. And the upper respiratory tract, most cats remain bright afebrile [00:04:00] and systemically. Well, it doesn't typically invade deeper tissues or cause things like pneumonia that is very rare. So this is mainly in ocular disease rather than a systemic one.

Transmission is primarily via direct contact with an infected cat, so the bacteria is shed in ocular and nasal secretions, so it can be transmitted via grooming for sharing food bowls, and especially queen to kitten transmission. It's common.

Because it is an obligate cellular pathogen, it really doesn't survive long in the environment, usually only a couple of hours, so contaminated surfaces and fomites are a much less significant source of infection. It also means that outbreaks are typically sustained through close, repeated contact between individuals rather than environmental contamination.

Clinical Signs

The hallmark sign of [00:05:00] feline Chlamydias is conjunctivitis. In the early phase of infection, cats might show some mild watery ocular discharge, slight conjunctival hyperemia, and maybe some sneezing. At this point, it's gonna look pretty mild and it might even resolve temporarily and then recur, so owners can miss it as, like we said, just an allergy or some mild irritation.

As infection progresses, the conjunctiva becomes really red, it becomes thickened that chemosis develops, and this is the swelling of the conjunctiva, so it can kind of look like fluid filled pillows, bulging around the eyelids. , And that is quite a hallmark sign of Chlamydias. The discharge can become muco perent, so thicker, and that yellow green color.

We can also see things like blepharospasm, ocular discomfort. The cat might be pouring at the face or [00:06:00] squinting and holding the eye closed, and in many cases the infection starts in one eye, but can progress to become bilateral. One key point, which does help differentiate chlamydia from herpes virus is that the cornea usually remains unaffected.

So chlamydia doesn't typically cause ulceration, and if you do see ulceration, it's more likely to to something like trauma or a foreign body or feline herpes virus, which causes that characteristic, dendritic or branching ulcer.

Diagnosis

So the next step is going to be deciding what to do for diagnostics. PCR is the most accurate and reliable diagnostic test, and it's typically performed on conjunctival swabs. It's gonna detect the bacterial DNA, and it's really sensitive and really [00:07:00] specific. It's good if we are dealing with recurrent cases, if we have multiple cats affected in.
The same environment. Or perhaps we had a poor response to empirical treatments and wanted to confirm the cause of disease. But in practice, the reality is PCR can be expensive and the turnaround for test.

Results might be several days, and we might wanna start treatment immediately. So in Tiki's case, for example, she's bright, she's young, she has that classic conjunctivitis, and she lives with three other cats who have had similar signs. So what we could do is send a swab to. Run a PCR to try and confirm chlamydia, but based on what we're seeing today and the history that the owner described, it's very likely to be that diagnosis.

We can start empirical treatment today and then reassess when the results come back or if she doesn't respond.

[00:08:00] A couple of other diagnostic options is cytology, so if we do a conjunctival swab, we might see basophilic. Intracytoplasmic inclusion bodies, so there's gonna be intracytoplasmic because these bacteria live inside the cells and they're gonna be basophilic. So blue purple structures inside the epithelial cells, but they can be easily missed.

And poor sample technique or a non-diagnostic sample or pore staining technique can all cause false negative tests. So cytology can support a diagnosis, but a negative result isn't gonna rule it out. Culture and serology are also options, but they're not routinely used in practice because culture is gonna require specialized media and lab conditions because that bacteria is intracellular.

It's also slow, it's quite expensive, and it's pretty much only used for [00:09:00] research. Antibody testing with serology can be used, but it can't distinguish between past exposure and current active infection. If we go ahead with empirical treatment. Response to treatment is used as part of the diagnostic process. So if we, for example, start antibiotics and Tiggy starts improving pretty quickly in the next couple of days, it's gonna support that diagnosis as a likely cause. But also remember that a couple of other pathogens could respond to treatment.

So it's not a definitive diagnosis. It's also worth noting that asymptomatic cats in the household, like Tiggy three companions can actually still be actively shedding the bacteria. So this is why we have to assume that all inContact cats have been exposed and are infected.

Treatment

[00:10:00]

The gold standard treatment for feline chlamydia is doxycycline. It is lipid soluble, so it has really good penetration in mucosal tissue and into cells. It also provides some coverage for mycoplasma bacteria, which is a common co-infection, or if it has a really similar presentation and maybe we're actually missing.

Diagnosing a mycoplasma infection with chlamydia, but it's also gonna cover mycoplasma. So we're pretty safe with doxycycline. For Tiggy, assuming she's a healthy adult with no underlying concerns, doxycycline is given orally once daily for a minimum of four weeks.
We must treat for the full four week course and not stop when the discharge clears or the eye starts to look a bit better because the infection can still be present. And then if we stop treating, don't use the full course. Don't kill all the bacteria. [00:11:00] Recurrence is very likely to occur. In Tiggy household, two of the other cats had previously shown similar signs, and they appeared to recover spontaneously, but they could be asymptomatic carriers of the disease and shedding the organism into the environment.

So making sure that we treat all cats in the household and being confident explaining why we're doing this with the owner. And that while they may not be showing clinical signs, the other cats are likely to be carriers, so it is just as important to treat them to prevent infection, recurrence,

doxycycline and cats can cause esophagitis and esophageal strictures by causing mucosal irritation. So owners I have to be confident in tableting their cats and following each of these doses with water or a small treats or a bit of a meal to make sure that that tablet is going down properly and [00:12:00] is not lodging in the esophagus causing inflammation.
The, the other thing we could do is prescribe a liquid formulation rather than a tablet, which some caps can tolerate better.

But checking compliance and checking that the owner is confident in tableting the animal is gonna be key for long-term compliance and treatment efficacy because no one wants to try and fight this grumpy cat to force a pill down their throat. And they're probably not gonna tell you that that is what the outcome has been.

So check before you prescribe to make sure that we are getting really good treatment compliance. We can also show owners how to tablet effectively or recommend things like pill pockets and soft treats to hide tablets in if they find their cat rechy to tablet.
In addition to antibiotics, we can also use some lubricating eyedrops to help soothe the [00:13:00] eyes. And we should also use warm water and saline to clean away those crusts and discharge.

Prevention

So now we have treated Tiggy and hopefully the other cats at home with a full course of doxycycline. Everyone's improving. And the conjunctivitis has cleared away.
But what can we do to make sure that this isn't going to occur again?

So there is a licensed vaccine for chlamydia in cats, but it is not a core vaccine. The current recommendations is that the chlamydia vaccine should be used strategically, not routinely. So it's basically reserved for. Situations like breeding colonies or shelters, rescue environments, um, multi cat households if infection has been confirmed, , or households with recurring conjunctivitis cases.

In Tiggy case, if this is the [00:14:00] second time it's happened or the other cats are now being treated again, you might start discussing whether the vaccination is a better long-term prevention tool. But we need to make sure that the owners know that the vaccine does not prevent infection entirely. It does not completely eliminate shedding, but it does reduce the severity of disease.

As we mentioned earlier, chlamydia. Felis is really not an environmentally tough bacteria. It's pretty easily killed by standard disinfectants, so cleaning is obviously helpful, but owners don't need to be doing like a full scrub, a full bleach. A full wash down of the house every day. We can just do some small things like regularly clean food bowls, clean the lit trays, make sure beddings fresh, wash any soft furnishings and cat toys that may have had contact with secretions, , and then limit contact between potentially infected [00:15:00] and non-infected cats to prevent spread.

Key Points

So what are the key things that you need to know about Feline Chlamydias? It is caused by chlamydia Phylis, which is an obligate intracellular bacteria that primarily affects the conjunctiva and the respiratory epithelium. Clinical signs include conjunctivitis, chemosis, ocular discharge, and spasm.

Diagnosis is confirmed with PCR, but many cases are diagnosed clinically based on classic signs and a history. The treatment of choice is doxycycline for at least a four week course, and we must be treating all in contact cats even if they appear healthy because they could be carriers of the bacteria.

Incomplete treatment courses or failure to treat the whole household are [00:16:00] really common reasons for infection recurrence. And then finally, prevention includes treating the whole group, maintaining really good hygiene, separating infected individuals, and using strategic vaccination if we have some really high risk animals.

Outro

And that is Bline Chds. So thank you so much for listening to this episode.
If you enjoyed it, please make sure to follow or subscribe wherever you get your podcasts. If you've got a friend revising for exams or a colleague who needs to brush up on this condition, then share it with them and you'll find the links to resources we used in the show notes.

And let us know if there's a topic you'd like to hear covered. Next, find us on Instagram and TikTok at Veterinary Vista and we'll see you next time.
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