PRESENTING SIGNS

Conjunctivitis can present in a number of ways in cats but conjunctival hyperaemia, a red eye, will always be a main owner concern. Since the presentation is similar regardless of cause, careful questioning of the owner regarding the progress of the disease, vaccination status, previous episodes and so on is required. In general, it is sensible to rule out the infectious causes, by far the most frequent cause for feline conjunctivitis, before considering other aetiologies such as allergy, neoplasia or tear film abnormalities.

Conjunctivitis can be seen as part of an upper respiratory disease in young kittens, with whole litters (plus sometimes the dam) being affected to varying degrees. When present as part of the cat ‘flu complex like this, due to feline herpes virus infection, corneal involvement is common, with ulceration and even perforation occurring. Older kittens and adults can present with a unilateral conjunctivitis which later becomes chronic and can affect both eyes. Although this is also associated with feline herpes virus (FHV-1), respiratory involvement is much less common. Chlamydophila felis is also frequently implicated in feline conjunctivitis and corneal involvement is very unusual. Both kittens (usually over 4 weeks of age) and adults can be affected and the conjunctivitis can be both acute and chronic, affecting one or both eyes.

CASE HISTORY

Normally the history is one of an acutely red, wet eye. The discharge is initially serous but becomes mucopurulent within a few days. Involvement can be unilateral or bilateral. If upper respiratory signs are present, then FHV-1 must be considered the most likely causal agent but other infectious processes could coexist. Checking the vaccination status of affected animals, including the dam if young kittens are presented, is important, but the condition can still develop in vaccinated cats, although usually in much milder forms.

Slightly older kittens and adults will normally present with a unilateral conjunctivitis and may have a history of previous episodes. The recurrences are most likely when the cat is stressed – for example, placed in a cattery, introduction of new cat(s) to the home, given a general anaesthetic, immunosuppressed for another reason (feline leukaemia virus or systemic steroid administration) and so on. The owner should be asked if any of these stress factors have occurred to their cat recently. Occasional sneezing might be reported but recrudescent FHV-1 is typified by chronic conjunctivitis, sometimes with corneal involvement, but not with full blown respiratory disease. Respiratory signs are not usually a feature of Chlamydophila infection.

Although less common than infectious causes, allergic conjunctivitis is recognized in cats, most frequently due to a topical hypersensitivity to prescribed medication. Chlortetracycline is notorious for this so if the history is of a conjunctivitis which initially responded to this drug, but then the cat developed a marked conjunctival hyperaemia, possibly with some attempts at rubbing or eyelid involvement, then an allergic component should be considered. Stopping all topical medication for several days can sometimes be curative!

CLINICAL EXAMINATION

General clinical examination is important for all cases of feline conjunctivitis. Acute infections with FHV-1 manifest as the ‘cat ‘flu’ complex in young kittens and older, unvaccinated cats, and thus both respiratory signs and a pyrexia are common. If no systemic involvement is noted, then careful ophthalmic examination is required. This should rule out secondary causes of conjunctivitis such as entropion or a conjunctival foreign body, as well as keratoconjunctivitis sicca (see Figure 10.1). The cardinal signs of conjunctival hyperaemia, chemosis and increased lacrimation with a serous or mucopurulent discharge are non-specific for the different causes of conjunctivitis and therefore further case work-up is necessary to reach a definitive diagnosis.

Careful corneal evaluation is required since ulceration or keratitis with evidence of vascularization and scarring could suggest FHV-1 over Chlamydophila. Any symblepharon or limbal damage could also point to FHV-1 as described in later sections. Any chronic conjunctivitis can lead to follicle formation and this is not pathognomonic for any particular aetiology. The use of rose Bengal, rather than fluorescein, as a corneal dye is recommended in suspected cases of FHV-1 conjunctivitis since this might highlight areas of corneal epithelial devitalization which manifest as dendritic ulcers – patho-gnomonic for FHV-1 – which are rarely highlighted with fluorescein alone.

Intraocular involvement is not a feature of feline conjunctivitis but clearly if any evidence of uveitis for example is noted, then the tentative diagnosis should be reviewed and further ocular evaluation undertaken. As always, both eyes should be thoroughly examined, even if only one appears affected on initial presentation.

CASE WORK-UP

Once the ophthalmic examination has confirmed that conjunctivitis is the clinical diagnosis, rather than any other ocular disease in which conjunctival involvement is a feature, then investigation of the possible underlying cause is required. However, this can be frustrating and inconclusive on occasion. Swabs should be taken of both conjunctiva and oropharynx and placed in combined viral and chlamydial transport medium (VCTM). These can be used for both virus isolation and the more sensitive polymerase chain reaction (PCR) which is available for Chlamydophila as well as FHV-1. Unfortunately, intermittent excretion of both agents can lead to false negatives and repeated sampling might be required in some cases. Serology is of no use in vaccinated cats and only of limited use for Chlamydophila since high titres are common and can remain for many months post-infection.

Cytology can be useful for C. felis by demonstrating intracytoplasmic inclusion bodies in the epithelial cells during the acute phase of the disease. It can also help identify allergic components or if secondary bacterial infections are present.

Conjunctival biopsy can be considered in atypical cases, particularly if a neoplastic process such as lymphoma or squamous cell carcinoma is suspected.

EPIDEMIOLOGY

Since the two most common causes of conjunctivitis in cats – FHV-1 and C. felis – are infectious in nature, outbreaks can occur in multi-cat households and in outdoor cats which come into contact with infected cats. Both agents are ubiquitous in the feline population. Other infectious causes such as M. felis and calicivirus are less common, and primary bacterial infections are uncommon in cats (although secondary infections do occur). Less common causes such as topical hypersensitivity or neoplasia will only occur on an individual cat basis.

Initial infection with FHV-1 will cause respiratory signs – rhinitis, tracheitis and bronchopneumonia – as well as ocular signs, with conjunctivitis and corneal involvement particularly in young kittens and unvaccinated cats. The disease is caused by the direct cytopathic effect of viral replication in the relevant epithelium. Incubation periods are typically 2–10 days, but vary according to the amount of virus present and its pathogenicity, and the acute phase of infection will last about 2 weeks. Up to 80% of infected cats become carriers, and the latent infection can reactivate under conditions of stress – new cats in the neighbourhood, building work at home, other illnesses or anaesthesia, immunosuppression, prescribed medication such as systemic steroids and so on. Even treating these cats can stress them sufficiently to exacerbate viral replication and so a balance often has to be met between the ideal treatment for the condition and the individual temperament of the cat and its severity of symptoms. The reactivation of latent virus can result in chronic conjunctivitis or many of the more severe sequelae of FHV such as symblepharon, corneal ulceration, sequestrum formation, keratoconjunctivitis sicca, stromal keratitis and chronic epiphora (due to punctal occlusion). Table 11.1 summarizes the ocular manifestations of FHV-1 infection.

Table 11.1 Ocular manifestations of feline herpes virus

Age

Clinical signs

2–4 weeks – primary infection

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