Page 1221 - Problem-Based Feline Medicine

59 – THE CAT WITH OCULAR DISCHARGE OR CHANGED CONJUNCTIVAL APPEARANCE 1213

In severe cases, symblepharon is a complication detection of herpesvirus, but is not often used
(adhesion of conjunctiva to conjunctiva or conjunctiva because of logistical difficulties in getting rapid
to cornea), and the puncta may be occluded causing results.
chronic epiphora. ● Serology is of limited usefulness. Antibody titers
tend to be of low magnitude after primary infection,
In severe infections, the conjunctiva may be covered in
sometimes reaching only 1:64 at 60 days after
a gray pseudomembrane (diphtheritic).
infection. High titers are rarely seen after recrudes-
In older cats with a carrier status, mild signs of cent infection.
herpesvirus infection may be seen after some form of ● Polymerase chain reaction (PCR) testing: DNA
stress. In these cases, the inflammation is less intense amplification of an amino acid sequence of the
and often only a serous discharge is present. These cats thymidine kinase gene is perhaps the most sensitive
may have a history of respiratory infection as a kitten. test available. Theoretically, the test could pick up
one strand of viral DNA. The high sensitivity of
Chronic serous ocular discharge can occur in older cats.
nested PCR tests may reduce specificity, because
Corneal involvement (keratitis) may occur 1–2 weeks non-viral DNA contaminants may be detected.
after initial signs. Keratitis is visible as corneal cloudi- – Conjunctival swabs and/or biopsies are used for
ness (edema and inflammation), and punctate or laboratory diagnosis using PCR or virus isola-
branching ulcers, which may coalesce to large ulcers. tion. Not all laboratories are equipped to do this
● Corneal perforation and secondary bacterial infection work. Check with your laboratory, as you may
may result in destruction of the eye; this occurs more have to send samples interstate or overseas for
often in young kittens (ophthalmia neonatorum). results.
● Herpesvirus keratitis often occurs in the absence
of active upper respiratory infection.
Differential diagnosis
Diagnosis
Calicivirus.
Acute ocular and respiratory signs in a young cat ● Tends to produce milder respiratory signs and less
suggest an infection with herpesvirus or calicivirus severe conjunctivitis and mucopurulent ocular dis-
infection. Herpesvirus tends to produce more severe charge. Ulceration of the tongue is classical.
conjunctivitis and mucopurulent ocular discharge
Chlamydophila felis conjunctivitis.
than calicivirus.
● Commonly only unilateral, followed days later as
Diagnosis is usually based on clinical signs, as it is bilateral disease.
often not cost effective to establish a definitive diagno- ● Serous to mucopurulent discharge, which may be
sis. Obtaining a definitive diagnosis is useful in chronic more copious than FHV-1 conjunctivitis.
cases, or when there is a persistent cattery problem. ● Conjunctival follicles form in chronic cases.
● Conjunctival swabs or scrapings taken with a spat-
Definitive diagnosis is based on a variety of tech-
ula may be positive to a fluorescent antibody test.
niques, of which polymerase chain reaction is the most
● Cytology specimens may demonstrate the presence
sensitive.
of intracytoplasmic inclusion bodies, which are
● Cytology. Intranuclear inclusions in epithelial cells
present in the first 2 weeks of infection.
can be demonstrated with immunoperoxidase stains
● Culture is very difficult, and requires the use of spe-
in some acute primary infections. This is not very
cific growth media sent to specialized laboratories.
reliable or cost effective.
● Immunofluorescence. Direct or indirect fluores- Mycoplasma felis and M. gatae.
cent-antibody techniques can be applied to ● It usually causes a mild form of conjunctivitis
corneal or conjunctival smears or tissue sections, ● Ocular discharge remains serous in nature.
but it has poor sensitivity. ● It has been reported to occasionally form a con-
● Virus isolation by demonstration of cytopathic junctival pseudomembrane with a thick white
effects in cell culture. This is the gold standard for discharge.