Feline Chlamydial Disease
Although disease caused by Chlamydophila felis in cats has been referred to as feline pneumonitis, chlamydiae rarely cause pneumonia in cats. Ch. felis is regarded as a primary conjunctival pathogen and infection always involves the eye, resulting in conjunctivitis and occasionally also causing signs of rhinitis, with sneezing and nasal discharge.
Etiology and Pathogenesis
Chlamydiae are obligate intracellular bacteria that form inclusions within the cytoplasm of epithelial cells. Although antibody titers to Chlamydophila felis are common in some cat populations, the organism is rarely isolated from clinically healthy cats. Cats with chlamydial conjunctivitis are generally <1 yr old, and cats 2–6 mo old appear to be at highest risk of infection. Cats with conjunctivitis that are >5 yr old are very unlikely to be infected, and cats <8 wk old may be less at risk because of the presence of maternal antibody. Transmission occurs as a result of direct, close contact between cats, because the organism survives poorly in the environment. Infected cats also shed chlamydiae from their rectum and vagina, although whether venereal transmission may occur has not been confirmed. There is weak evidence that chlamydiae may be capable of causing reproductive disease and lameness in cats, although these associations have not been definitively documented.
Clinical and Pathological Findings
The incubation period after exposure to an infected cat ranges from 3 to 10 days. Signs can include serous to mucopurulent conjunctivitis, nasal discharge, and sneezing. Cats with signs of rhinitis in the absence of conjunctivitis are unlikely to be infected with Chlamydophila felis. Early signs include unilateral or bilateral conjunctival hyperemia, chemosis, and serous ocular discharge, with prominent follicles on the inside of the third eyelid in more severe cases. Corneal disease is rare, and if present, may be the result of co-infection with organisms such as feline herpesvirus 1. The signs are most severe 9–13 days after onset and then become mild over a 2- to 3-wk period. In some cats, clinical signs can last for weeks despite treatment, and recurrence of signs is not uncommon. Untreated cats may harbor the organism for months after infection.
Chlamydial conjunctivitis in cats should be differentiated from conjunctivitis caused by feline herpesvirus 1 and feline calicivirus. Diagnosis can be confirmed by demonstration of intracytoplasmic chlamydial inclusions in exfoliative cytologic preparations, by isolation of the chlamydial organism in cell culture, or by PCR for chlamydial DNA on conjunctival swabs. Scrapings for cytologic examination are prepared by lightly but firmly moving a spatula over the conjunctiva and smearing the scraped material onto a glass slide; the preparation is air-dried and stained.
Source: Merck Veterinary Manual