What is Chlamydophila Felis?

Chlamydophila felis (formerly Chlamydia psittaci var. felis) is an obligate intracellular bacterium — meaning it can only replicate inside living cells — that primarily infects the conjunctival epithelium of cats. It is one of the identifiable causes of feline upper respiratory infections and is particularly associated with chronic or recurrent conjunctivitis (eye inflammation).

Chlamydophila felis infection is most commonly seen in multi-cat environments such as catteries, shelters, and breeding colonies, where close contact facilitates transmission.

Symptoms

The hallmark of Chlamydophila infection is eye disease:

  • Conjunctivitis: Redness, swelling, and discharge from one or both eyes (often starts unilateral, then becomes bilateral)
  • Watery eye discharge progressing to thick, yellow-green mucoid discharge
  • Squinting and excessive blinking
  • Mild sneezing and nasal discharge
  • Slight fever
  • Mild lethargy

Unlike FHV-1 or FCV infections, Chlamydophila rarely causes severe systemic illness. However, chronic untreated infections can persist for weeks to months, causing significant discomfort.

Kittens aged 5–12 weeks are most commonly and severely affected.

Transmission

Chlamydophila spreads through:

  • Direct close contact between cats (eye and nasal secretions)
  • Contaminated hands of caregivers

The bacterium is fragile outside the host and does not survive long in the environment. It requires close, prolonged contact for transmission, which is why it is primarily a problem in multi-cat settings.

Diagnosis

Diagnosis can be confirmed through:

  • PCR testing: The most reliable method, using conjunctival swabs
  • Culture: Possible but difficult due to the intracellular nature of the organism
  • Clinical suspicion based on characteristic eye signs, especially in young cats from multi-cat environments

Vaccination

The Chlamydophila vaccine is a non-core vaccine with specific indications:

  • Recommended primarily for cats in multi-cat environments where the infection has been confirmed
  • Not generally recommended for single-cat households or cats with minimal contact with other cats
  • The vaccine reduces the severity of clinical signs but does not completely prevent infection

Vaccination Schedule

  • Kittens: Two doses starting at 9 weeks, 3–4 weeks apart
  • Adult cats: Two doses 3–4 weeks apart
  • Boosters: Annually, as long as risk factors persist

Treatment

Chlamydophila responds well to antibiotic treatment:

  • Doxycycline is the treatment of choice (3–4 weeks)
  • Topical antibiotic eye drops can be used in conjunction
  • All cats in the household should be treated simultaneously to prevent re-infection
  • Complete the full course of antibiotics, even if symptoms resolve early

Important Notes

  • Chlamydophila felis is not the same as Chlamydia trachomatis (which causes disease in humans). The risk of transmission to humans is extremely low, though basic hygiene is always recommended when handling cats with eye infections.
  • Breeding catteries with a history of the infection should implement a vaccination and treatment program for all cats in the colony.
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