Feline conjunctivitis can be a challenging condition to treat, both for vet and owner. Its tendency to recur often leads to client frustration, with vets understandably performing a number diagnostic tests and reaching for multiple treatments. Ron Ofri DVM, PhD, DECVO, who led last week’s webinar, questioned if these diagnostic tests and multiple treatments were really necessary and whether, in some cases, they could actually be making the situation worse.
Ron’s first piece of advice was to always remember that ‘cats are not small dogs’ and consequently need to be managed in a completely different way. Most cases of canine conjunctivitis occur secondary to a primary cause usually due to a condition causing chronic irritation such as exposure in brachycephalic breeds or ‘dry eye’. However, most cases of feline conjunctivitis are usually caused by primary pathogens, the main two being feline herpes virus (FHV-1) and Chlamydia felis (C.felis). Ron explained that diagnostic tests to try to confirm the presence of the primary pathogen in cats are rarely useful, as it can be challenging to isolate both chlamydia and FHV-1, and rather than spending the owner’s money on diagnostic tests, it would be much better to base a diagnosis on clinical signs and response to therapy.
Understanding the difference between FHV-1 and C.felis infection in cats is the key to differentiating between the two conditions. In primary herpetic disease, the young cat or kitten usually presents with acute bilateral conjunctivitis, often with severe discharge, whereas the cat (usually less than 5 years old) presenting with C.felis usually presents with a mild conjunctivitis, sometimes with chemosis, and responds well to treatment with tetracycline. Also feline conjunctivitis associated with FHV-1 can be recurrent as the virus will always sit latent within the trigeminal nerve, whereas conjunctivitis associated with C.felis is not recurrent. So for those recurrent cases of feline conjunctivitis, it is most likely that the underlying cause is the recrudescence of FHV-1 in times of stress. Cats with FHV-1 may also suffer from corneal ulceration which either present as a dendritic ulcer or a geographical ulcer. Again, cats infected with C.felis are very unlikely to suffer from corneal ulceration.
Tetracycline is usually the first treatment advised by Ron for cats with mild conjunctivitis and if their conjunctivitis resolves, then it is likely they were suffering from C.felis. However, antiviral treatment may be necessary in cases of recurrent feline conjunctivitis, or for cats with associated corneal disease where it can be assumed that FHV-1 is the underlying cause. Ron explained that the drugs used for treating FHV-1 are all virustatic rather than viracidal, so it is imperative to understand when treating these cats that our aim is to push them back into a latent state rather than to achieve an actual ‘cure’. Trifluridine and Idoxuridine can be used as topical eye drops but these have to be administered five times a day which, given the stress this may cause, may not be the best treatment course. Oral medication such as famciclovir is preferable as it only has to be given twice daily with its efficacy having been demonstrated at 90mg/kg q12hrs. However famciclovir is the prodrug which gets metabolised to the active drug penciclovir. Ron advised that penciclovir is available as a cream for humans called ‘Fenlips’ which can be placed in the cat’s eye 2-3 times a day and has shown to be effective. It is also important to consider the application of hyaluronic based artificial tears, as often dry eye can develop through a number of different mechanisms. The application of several eye drops, however, has to be measured against the amount of stress which is being caused to the cat, as this could inevitably be making things worse. Ron explained that at some point it may just be better to minimise stress and ‘dare to stop’ all medication.
Ron’s webinar was overflowing with really useful information which should prove invaluable when faced with a challenging case of feline conjunctivitis. For this reason, I would strongly advise watching this webinar as I have only been able to offer just a fraction of Ron’s practical tips and advice within this blog. There were, however, some key take home messages that Ron wanted to deliver, including that FHV-1 and C.felis are the leading cause of conjunctivitis in cats, that a diagnosis should be based on clinical signs and response to therapy, that recurrent conjunctivitis and keratoconjunctivitis suggests FHV-1 infection, and to always consider the level of stress you are putting these patients through when treating for this condition because you may just be making matters worse rather than better!