Feline Pneumonitis (Feline Chlamydial Infection)
Introduction
Feline pneumonitis is a contagious respiratory disease of cats primarily affecting the upper respiratory tract and conjunctiva. It is most commonly associated with Chlamydia felis infection and is characterized by conjunctivitis, nasal discharge, and mild respiratory signs. The disease is especially important in multi-cat households, shelters, and breeding catteries.
Etiology
Causative Agent
Feline pneumonitis is caused by Chlamydia felis, an obligate intracellular bacterium.
Organism Characteristics
- Gram-negative-like intracellular bacterium
- Two developmental forms: elementary body (infectious) and reticulate body (replicative)
- Primarily infects epithelial cells of conjunctiva and respiratory tract
- Survives poorly in the environment outside the host
Epidemiology
Species Affected
- Domestic cats (primary host)
- Occasionally other felids
Age Susceptibility
- Most common in kittens and young cats
- More severe in immunocompromised animals
Transmission
- Direct contact with ocular and nasal secretions
- Aerosol transmission in close-contact environments
- Fomites (less important due to low environmental survival)
Risk Factors
- High-density housing (shelters, catteries)
- Poor ventilation
- Stress (weaning, transport, overcrowding)
- Lack of vaccination
Pathogenesis
Initial Infection
The organism enters via the conjunctiva or respiratory tract and infects epithelial cells.
Local Replication
- Multiplication in conjunctival and nasal epithelium
- Cell damage leads to inflammation
Inflammatory Response
- Marked conjunctivitis due to immune response
- Mucopurulent discharge from eyes and nose
Systemic Spread
Systemic infection is uncommon; disease remains primarily localized to eyes and upper respiratory tract.
Clinical Signs
Ocular Signs (Most Prominent)
- Unilateral or bilateral conjunctivitis
- Conjunctival hyperemia (redness)
- Chemosis (swelling of conjunctiva)
- Ocular discharge (initially serous, then mucopurulent)
Respiratory Signs
- Mild sneezing
- Nasal discharge
- Mild coughing (occasionally)
Systemic Signs
- Mild fever
- Depression
- Anorexia in severe cases
Chronic Infection
- Persistent or recurrent conjunctivitis
- Long-term carrier state possible
Summary for Practitioners
Feline pneumonitis should be suspected in young cats with persistent conjunctivitis and mild upper respiratory signs, especially in multi-cat environments.
Postmortem Findings
Gross Lesions
- Conjunctival inflammation and edema
- Mild rhinitis
- Occasional tracheitis
Microscopic Lesions
- Conjunctival epithelial cell necrosis
- Inflammatory infiltration (neutrophils and lymphocytes)
- Intracytoplasmic inclusions in epithelial cells
Diagnosis
Clinical Diagnosis
Based on characteristic conjunctivitis and respiratory signs in cats, especially in group housing systems.
Laboratory Diagnosis
- PCR for detection of Chlamydia felis
- Conjunctival swabs for cytology
- Serology (supportive but less definitive)
Differential Diagnosis
- Feline herpesvirus-1 (FHV-1)
- Feline calicivirus
- Mycoplasma spp. infection
- Bacterial conjunctivitis
Summary for Practitioners
Differentiation from viral causes of feline upper respiratory disease is essential, as co-infections are common.
Treatment
Antibiotic Therapy
- Tetracyclines (e.g., doxycycline) are the treatment of choice
- Alternative antibiotics: macrolides or fluoroquinolones in some cases
- Prolonged treatment (2–4 weeks recommended)
Supportive Care
- Ophthalmic cleaning and hygiene
- Lubricating eye drops (supportive)
- Improved nutrition and hydration
Summary for Practitioners
Early antibiotic treatment is highly effective. Relapses may occur if treatment duration is inadequate.
Control and Prevention
Vaccination
- Available in combination vaccines for cats
- Reduces severity of clinical signs but may not prevent infection
Biosecurity
- Isolation of infected cats
- Quarantine of new arrivals
- Good hygiene in multi-cat environments
Environmental Management
- Reduce overcrowding
- Improve ventilation
- Minimize stress factors
Summary for Practitioners
Control relies on vaccination, hygiene, and management of group-housed cats to reduce transmission.
Zoonotic Importance
Chlamydia felis is rarely zoonotic. Human infection is extremely uncommon but may occur in immunocompromised individuals in close contact with infected cats.
Economic Importance
Feline pneumonitis leads to veterinary treatment costs, reduced breeding performance in catteries, and persistent morbidity in shelter populations.
Summary
Feline pneumonitis is a chlamydial infection of cats characterized mainly by conjunctivitis and mild respiratory disease. It is common in multi-cat environments and is effectively managed through antibiotics, vaccination, and good husbandry practices.
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