Mastering feline conjunctivitis cases
Runny, puffy, and red eyes? Oh no!
I love my feline patients, but most of them are battling similar issues – red and puffy eyes that will not get or stay better. Our best treatment strategies are based on knowing the most common causes of feline conjunctivitis, how to diagnose it and how to treat it.
When a cat presents with a history of red eyes, squinting or watery discharge, it is important to do a complete ophthalmic exam and create a problem list. Limited kitty minutes? Be sure to have all of your tools together before starting the exam, and remember that checking for an ulcer is an important part of this assessment. Once you have completed a fluorescein stain, looked for any irritants (eyelid masses, hairs), and found the intraocular exam is normal, you conclude that feline conjunctivitis is the diagnosis.
In cats, the most common underlying cause for conjunctivitis is an infectious etiology. This includes feline herpesvirus-1 (FHV-1), Chlamydia felis, and Mycoplasma spp, among the most common.
Diagnosis
Each of these organisms is treated differently, so being able to narrow down a more specific diagnosis will help guide treatment decisions. Preferred samples can include a conjunctival swab or a swab of the oropharynx if the cat has respiratory signs.1 Polymerase chain reaction (PCR) testing is considered the best diagnostic for the most common organisms, and your preferred lab may even offer a feline respiratory panel that would screen for them all. As we continue to discuss these organisms below, it is important to remember that false negatives and false positives can occur. Understanding your results is an especially important step because no test is perfect, and therefore, we often rely heavily on the overall clinical picture.
Feline Herpesvirus-1
FHV-1 is considered common, especially among shelter-housed cats. Following an acute episode, 80% of cats develop a latent stage where the virus resides in the trigeminal nerve and waits to recrudesce in times of stress or immunosuppression.2 These cases will have a few different presentations:
The acute infection: Following exposure, acute clinical signs can develop within 2-6 days and last 10-20 days.1 These signs can include conjunctival hyperemia, ocular discharge, corneal ulceration and squinting. They may or may not have respiratory signs. Infection is typically self-limiting, and not all cats require anti-viral treatment. It is also important to know that secondary bacterial infections are common. If signs are severe in an adult cat or last longer than a few weeks, adding an anti-viral would be indicated.
The recrudescent patient
This patient can have the same signs as an acute patient, and they may also have a history of episodes of conjunctivitis. Treatment in these patients is the same as the acute patient, but it becomes important to understand what triggers these episodes. Has there been a recent stressful event in the home or cat’s life such as moving, traveling or a new animal in the house? Adjusting the environment becomes important with the goal of limiting stress to decrease the number of flare-up events.
The recrudescent patient, advanced version
These are the tricky ones. These patients will have signs of blood vessel growth throughout their cornea (keratitis) because their immune system has mounted a response within the cornea (Figure 1). Their clinical signs are more often a result of their immune system creating inflammation on the ocular surface than actual active viral disease. 2 I will often complete a course of anti-viral therapy if one has not been done to ensure the virus is no longer contributing but more often, these patients benefit from topical immunomodulatory therapy.
Figure 1: Stromal vessels growing across the cornea of chronically affected cat. (Image courtesy of Mary Lucille Walsh, DVM, DACVO)
Additionally, FHV-1 is not only associated with conjunctivitis and superficial ulceration but has also been correlated with corneal sequestrums and eosinophilic keratitis. When treating these conditions, adding an anti-viral may also be of benefit. 3
Diagnostics
PCR testing can help obtain a diagnosis of FHV-1; however, since co-infection is also very common in these cases, PCR can help identify if there is a second organism that requires treatment. If FHV-1 reveals a negative result on PCR, either the patient is truly negative, they are no longer shedding, the sample is inadequate, or the sample degraded in transport. 1 If FHV-1 reveals a positive result on PCR and the clinical signs support diagnosis, then we feel confident in treatment.
Anti-viral Therapy
The most common anti-viral therapies include idoxuridine 0.1% topical solution, cidofovir 0.5% topical solution and famciclovir oral tablets. I strongly recommend considering two things when selecting your therapy:
- Can the owner easily give a drop OR a tablet?
- How do I minimize the number of therapies and achieve maximal success?
Why do I approach every case with these questions? Stress can contribute to the recurrence of signs, so we are working against ourselves by asking an owner to do multiple therapies that force the cat to hide all day. We also want to set our owners up for success. The eye drop is only effective if it actually makes it off the counter and onto the eye. We want successful treatment that also maintains a good relationship between the veterinarian, the owner and the patient.
Idoxuridine is most effective 5-6 times per day, well tolerated by cats, but is not thought to be effective in our cases of keratitis (see recrudescent, advanced version) because that is isolated deeper within the cornea. Cidofovir is effective at two times per day, well tolerated (but personal experience has shown some cats are reactive) and believed to be effective for all versions of clinical disease.2,3 Famciclovir is an oral medication with the best formulation as a tablet. It is a very effective anti-viral, but the tablet size can be quite large which is challenging for owners to administer. There are compounded formulations available, but studies have shown that the dose is not consistent throughout the provided bottle which can then impact treatment response.4
Chlamydia felis
Also quite common in shelter-housed communities, this organism has a predilection for conjunctival epithelial cells. Therefore, it’s thought that C. felis will produce more chemosis (“puffiness”) vs FHV-1, which has more predominant hyperemia. Incubation lasts about 2-5 days, and clinical signs can persist for up to 2 weeks.2 Generally, acute infection will cause watery discharge, squinting and chemosis, but this organism does not cause ulceration like FHV-1. PCR testing is an excellent way to confirm a diagnosis of active infection and screen for any possible co-infections. Systemic doxycycline is an effective treatment and should cure clinical disease after 3-4 weeks of therapy. 2 This organism is also susceptible to oral fluoroquinolones. Still, care should be taken considering the risk of retinal toxicity in this species. Topical therapy with erythromycin can also be considered, as it will improve clinical signs and target the organism. Unfortunately, it does not always eliminate infection if the organism.
Mycoplasma spp.
While multiple spp. have been isolated from feline conjunctival samples, Mycoplasma felis and Mycoplasma gateae are thought to be the most common. Clinical signs are non-specific, including discharge, hyperemia and chemosis. PCR testing is an excellent diagnostic tool in confirming your diagnosis. The recommended treatment includes doxycycline for at least 2 weeks.2 A topical tetracycline could also be used, but there is some resistance to macrolides, so erythromycin or azithromycin may be less effective.
