www.ivis.org Proceeding of the SEVC Southern European Veterinary Conference Oct. 17-19, 2008 Barcelona, Spain http://www.sevc.info Reprinted in the IVIS website with the permission of the SEVC www.ivis.org
Ophthalmology Diagnosis and Management of Conjunctival Disease in the Cat Dr.E.Bjerkaas Norwegian School of Veterinary Science Infectious disease Conjunctival disease is most frequently associated with infection of the upper respiratory tract (URT) disease, so called cat flu. FHV-1 and FCV account for about 80% of the cases, but by tradition, four infectious agents have been associated with upper respiratory tract disease and conjunctivitis in cats: Feline Calicivirus (FCV), Feline herpesvirus (FHV-1, formerly termed feline rhinotracheitis virus), Chlamydophila felis and Mycoplasma spp. Bordetella bronchiseptica is a bacteria causing upper respiratory signs, but affected cats do not show concurrent conjunctivitis. URT disease is spread primarily through direct contact between cats, large amounts of virus being present in the saliva, tears and nasal discharges of cats with clinical signs. The vira are able to survive in the environment for up to a week. Thus, virus can also be transmitted through clothing, food bowls and other objects. Feline calicivirus (FCV) This is an important cause of upper respiratory tract disease in domestic cats, particularly in large cat groups like breeding colonies and rescue shelters. It is a major pathogen of the domestic cat, with clinical signs including oral vesicular disease and chronic stomatitis. Calicivirus-infection has been associated with conjunctivitis in cats. Experimental inoculation with calicivirus in cats has not produced ocular signs as response to infection, however. The significance of this virus in conjunctivitis may therefore be worth further studies. Some strains of the FCV may even cause more serious disease, including lameness, swelling of the head and paws, jaundice and bleeding from the nose and the bowel. The vast majority of cats only develop URT disease signs, however. FCV is a small, highly variable RNA virus that has the ability to change rapidly or evolve. This variability has important implications for designing vaccines, as many vaccines are very effective at preventing clinical disease, but they do not prevent infection. Thus, in spite of widespread vaccination, prevalence of FCV is still very high. Feline herpesvirus (FHV-1) FHV-1 is a large DNA virus that, unlike FCV, shows little variation in serotype. FHV-1 is a very common pathogen, studies in the USA have shown that abut 75% of the adult cat population is seropositive and that the virus may be responsible for about one-half of all respiratory diseases in cats. The epiteliothrophism and neurotrophism of the virus account for the major clinical features, destruction of epithelial cells and latency established in the trigeminal ganglia after primary infection. After infection, a chronic carrier state develops with intermittent virus shedding in about 45% of the cats. Recurrence is common, especially with stress or other systemic disease. However, the exact mechanism of reactivation is not understood. The virus is transmitted by direct or indirect contact and the mode of infection is considered to be inhalation. After a short (2-6 days) incubation period after primary infection, clinical signs of serous ocular and nasal discharge, sneezing, decreased appetite and fever are noted. Most conjunctivitis are serous in the initial stage, but conjunctivitis is often further aggravated by secondary bacterial infection. Newborn kittens may develop ophthalmia neonatorum with swelling of eyelids and discharge if infected before the eyes are opened. Older kittens with primary infection develop serous conjunctivitis with
chemosis and subsequent conjunctival epithelial necrosis. Corneal changes are seen as superficial branching ulcera, so-called «dendritic ulcera». These changes are often too superficial to be diagnosed by staining with fluorescein; however staining with rose-bengal may be diagnostic. Symblepharon formation (adhesion of conjunctiva to itself or to the cornea) is not an uncommon sequel of primary FHV-1 infection and is caused both by the concurrent conjunctival swelling and epithelial necrosis of the conjunctiva and cornea, as well as the destruction of the stem cell population at the limbus. The infection may also progress to corneal perforation, endophthalmitis and phthisis. Older cats with signs of recrudescent FHV-1 infection may show only moderate signs of systemic disease. The ocular changes are often more severe than in primary infection, however. Corneal changes are often unilateral and present as superficial keratitis with dendritic or geographic epithelial defects due to virus replication, or as stromal keratitis. Stromal keratitis is probably not caused by active viral replication, as virus is rarely isolated from these ulcers. The changes of the corneal stroma may, however, be the result of a hypersensitivity reaction to viral antigens in the stroma. Corneal sequestration (corneal necrosis - «black body») is a non-specific response to keratitis, but FHV-1 is considered a contributing factor in many cats. Chronic conjunctivitis may cause keratoconjunctivitis sicca because of obstruction of the lacrimal gland ducts. Diagnosis can be established by cultivation of virus and by PCR methods, however false negative and also positive results are not uncommon. Thus, most cases are diagnosed by clinical signs. Treatment of primary infection is symptomatic and supportive. Antibiotics may be indicated for secondary bacterial infection. The condition responds unpredictably to anti-viral agents and there is, at present, no drug or combination of drugs which can be recommended as the treatment of choice. Topical treatments require frequent application, the most effective drugs being thrifluorothymidine (Viroptic ), idoxuridine (Iducher ) and vidarabine (Vira-A ). Oral therapy with antiviral agents offers an alternative approach, but toxic side effects may limit the use of some agents. Recently, oral treatment with famciclovir (Famvir ) 1/8 of a 125mg tablet daily to average-sized cat, has been fairly widely used; however, tests of possible side effects have not been published. Cidofovir 0,2% topically twice daily has shown promising results in resent research. Dietary therapy with L-lysine (200-500 mg mixed with the food twice daily) is used empirically as a means of suppressing FHV-1 replication in cats. Topical and oral interferon has been used in acute FHV-1 infections, although controlled trials have not been convincing. Lactoferrin (mammalian iron-binding glycoprotein) has antiviral properties. An effect in vitro through inhibition of virus adsorption to the cell surface and penetration into the host cell has been shown, but controlled studies in cats are at present lacking. The most efficient way of controlling FHV-1 infection may be through preventive measures in exposed catteries. Breeding carrier cats are a risk to their kittens as the stress of kittening may precipitate shedding of FHV-1. Chlamydophila felis Chlamydophila felis (formerly Chlamydia psittaci) is a primary conjunctival pathogen in cats, and spreading to other cats within a household is not uncommon. In the UK, Chlamydophila accounts for about 30% of acute conjunctivitis in cats, and is also a common cause of chronic conjunctivitis. While mostly younger cats suffer from chlamydial conjunctivitis, perinatal chlamydial infection may also represent a cause of ophthalmia neonatorum, and adult cats may be infected. Incubation period is short. Nasal discharge and sneezing may not be so prominent as in calicivirus- and FHV-1 infections. Initially conjunctivitis is unilateral, but most often spreads to affect the other eye as well. Clinical signs include serous ocular discharge, blepharospasm, conjunctival hyperaemia and chemosis. Conjunctival follicles may be present, but this can occur in any chronic conjunctivitis. After infection, organisms are shed for a long period of time, and may also be excreted through the urogenital and gastrointestinal systems.
Diagnosis is established mostly through PCR testing, although in the initial stage basophilic intracytoplasmic inclusion bodies may be identified in conjunctival scrapings. Although different from the human strain, there are similarities, and there are a few reports for the feline strain suspected to cause infections in humans. The zoonotic aspect should therefore be considered when treating affected animals. Mycoplasma spp. Mycoplasma spp. is a common finding in the normal conjunctival flora of cats, but its role in causing conjunctivitis in normal cats has been questioned. This may suggest that Mycoplasma species are rarely pathogenic unless the animal is immunosuppressed or there is a concurrent infection with Chlamydophila or FHV-1. Therapy considerations for conjunctivitis A common approach to acute feline conjunctivitis is to treat what is most easily treatable. Thus, symptomatic therapy is directed at controlling Chlamydophila felis since a primary viral infection is usually self-limiting within 10-14 days. Also in chronic conjunctivitis therapy for the adult cat is directed against Chlamydophila. If no response to therapy within 3 weeks, FHV-1 can be suspected, and further therapy is aimed at controlling this infection. One should remember that tetracyclines may cause dental staining in young animals. Conjunctivitis of non-infectious origin Eosinophilic keratoconjuncitivitis This type of conjunctivitis is considered immune mediated, although infections with both FHV-1 and Chlamydophila have been implicated as a cause or as a secondary opportunist. Both cornea and conjunctiva are usually affected. The disease is most often unilateral, but bilateral disease dose occur. Treatment consists of topical corticosteroids in tapering doses as clinical signs resolve. Lifelong treatment is most often necessary, however. Keratoconjunctivitis sicca This is an uncommon disease in the cat unless related to infection with FHV-1. Measurement of tear production using Schirmer Tear Test is not always reliable, as stress lowers the readings. Thus, one has often to rely on both STT-results and clinical signs, although these are usually not so prominent in cats than in dogs. Treatment of KCS is as in dogs. Allergic conjunctivitis Conjunctivitis caused by allergies or chronic irritants occurs in cats. Rubbing and frequent blinking may be a clinical feature together with conjunctivitis. The primary cause may be difficult to determine, however. Treatment is symptomatic after infectious causes have ben ruled out. Lipogranulomatous conjunctivitis Older cats may develop an inflammatory reaction to lipids, presumably from the Meibomial glands. Surgical treatment is indicated when the inflammation causes problems. Secondary conjunctivitis The most common cause of secondary conjunctivitis is eyelid defects. In young cats, agenesia of the lateral part of the upper eyelid may be seen. Entropion is not uncommon, but may be missed on superficial examination. Treatment consists of correcting the eyelid defect. Entropion secondary to chronic conjunctivitis also occurs in cats, demanding both treatment of the infection as well as surgical correction of the eyelids. Suggested reading
- BSAVA Manual of canine and feline infectious diseases (2001) eds. Ramsey I & Tennant B. - Andrews SE (2008) Immune-mediated canine and feline keratitis. In: Veterinary Clinics of North America, Small Animal Practice 38: 269-290. - Stiles J. (2000) Feline herpesvirus. Veterinary Clinics of North America 30: 1001-1014. - Maggs DJ, Clarke HE. (2004) In vitro efficacy of gancyclovir, cidofovir, penciclovir, forscarnet, idoxuridineand acyclovir against feline herpesvirus type-1. AmJ Vet Res 65: 399-403. - Read RR& Lucas J. (2001) Lipogranulomatous conjunctivitis: clinical findings from 21 eyes in 13 cats. Vet Ophth 4; 93-98. www.fabcats.com