Prevalence of feline herpesvirus 1, Chlamydophila felis, and Mycoplasma spp DNA in conjunctival cells collected from cats with and without conjunctivitis

Aetiology of corneal ulcers assume FHV-1 unless proven otherwise

OVERVIEW

Feline ulcerative keratitis is a common presenting complaint and is frequently a sequela of feline herpesvirus 1 (FHV-1) infection; so much so, in fact, that it is fair to assume an FHV-1 aetiology until proven otherwise. Other potential causes of ulceration are trauma or underlying eyelid abnormalities (entropion, ectropion, agenesis, dermoids, neoplasia), lash abnormalities (ectopic cilia, trichiasis), tear film abnormalities or neurological deficiencies (trigeminal nerve paralysis, facial nerve paralysis).

CLINICAL CHALLENGES

The management of corneal ulceration in cats is frequently challenging, and treatment needs to be tailored carefully to the individual cat, its temperament, and the disease process present.

EVIDENCE BASE

The scientific literature on feline ulcerative keratitis is extensive, particularly that related to FHV-1 infection. The aim of this article is to review the aetiology and diagnosis of corneal ulceration in cats with particular reference to the evidence base available.

PATIENT GROUP

All age groups and breeds can suffer with ulcerative keratitis. Breed predispositions are present for some forms of corneal ulceration, and these are discussed.

Infectious disease diagnostic assays

Dogs and cats are commonly exposed to infectious disease agents. The following article is an update on the most common infectious disease assays used in small animal practice. In some situations, results of pathogen-specific molecular diagnostic assays can be used to assist the practicing veterinarian in the management of patients with infectious diseases. However, with some infectious disease agents, the assays are positive in healthy and ill animals and can be falsely negative and so the predictive values of the assays vary.

Chlamydophila felis CF0218 is a novel TMH family protein with potential as a diagnostic antigen for diagnosis of C. felis infection

Chlamydophila felis is a causative agent of acute and chronic conjunctivitis and pneumonia in cats (feline chlamydiosis). Also, C. felis is a suspected zoonotic agent of such diseases as non-Chlamydia trachomatis conjunctivitis in humans, although this is controversial. At present, there is no serodiagnostic system that specifically detects C. felis infection conveniently. Current systems use antigens such as lipopolysaccharide that cross-react with all chlamydia species. In addition, it is difficult to distinguish between cats that are vaccinated with the commercial vaccine against C. felis and cats that are infected with C. felis. Here, we describe a new candidate diagnostic antigen for diagnosis of C. felis infection, CF0218, that was obtained by screening a genomic expression library of C. felis Fe/C-56 with C. felis-immunized serum. CF0218 was a putative transmembrane head (TMH) family protein with bilobed hydrophobic motifs at its N terminus, and orthologues of CF0218 were not found in the Chlamydophila pneumoniae or Chlamydia trachomatis genomes. The recombinant CF0218 was not recognized by antiserum against C. trachomatis, suggesting that CF0218 is C. felis specific. CF0218 transcription during the course of C. felis infection was confirmed by reverse transcription-PCR. By indirect immunofluorescence analysis, CF0218 was colocalized with the C. felis-formed inclusion bodies in the infected cells. The antibody response against CF0218 was elevated following C. felis infection but not by vaccination in experimentally vaccinated and infected cats. These results suggest that CF0218, a novel TMH family protein of C. felis, possesses potential as a C. felis infection-specific diagnostic antigen.

Detection of virulent feline herpesvirus-1 in the corneas of clinically normal cats

To evaluate the clinically normal feline cornea for the presence of virulent feline herpesvirus-1 (FHV-1), corneas from 31 cats (25 with normal eyes and six with active disease or corneal scarring) euthanased at a shelter were collected. Corneas from two specific pathogen-free cats were included as negative controls. Virus isolation (VI), fluorescent antibody (FA) staining and real-time polymerase chain reaction (rt-PCR) were performed on all samples. The presence or absence of dexamethasone in the media was evaluated for its effect on VI. VI was positive for FHV-1 in six corneas from five cats, all with clinically normal eyes. One cornea was positive for feline calicivirus (FCV) in addition to FHV-1, but only in media that included dexamethasone. Eight corneas were positive on rt-PCR for FHV-1, all from cats with clinically normal eyes. All positive VI samples were confirmed with FA staining. VI and rt-PCR were negative for FHV-1 and FCV in cats with active disease or corneal scarring. Data from this study indicate that virulent FHV-1 and FCV can be present in feline corneas that are clinically normal. Dexamethasone may enhance viral spread through a cell receptor mechanism.