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devoted to Persian & Exotic Shorthair Cats

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The Premier Online Magazine devoted
to Persian & Exotic Shorthair Cats

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Chlamydia In Cats

There are many strains of Chlamydia bacteria, each strain usually being specific to one species of animal. The strain of Chlamydia that infects cats is exclusive to cats and rarely, if ever, causes disease in other animals. Chlamydia in cats is more correctly called Feline Chlamydiosis and is caused by a bacterium called Chlamydia psittaci var felis.

Chlamydia was originally identified from the lung of a cat with pneumonia, and at one time the disease was called “feline pneumonitis”, a term still sometimes used.


Chlamydia is most often seen in kittens and the symptoms are very “flu-like”. Symptoms include:

  • Conjunctivitis: Reddened and swollen conjunctiva, commonly called “pinkeye”
  • Conjunctivitis is often initially in one eye but may be seen in both eyes
  • Eye discharge is thin and clear progressing to thick and pale yellow
  • Mild sneezing
  • Runny nose and eyes
  • Squinting
  • Lesions may develop on the eye
  • Conjunctivitis may become chronic, especially if the cat also has herpes virus (which is fairly common)
  • Occasionally the cat may develop a mild fever
  • Usually the cat continues to be energetic and eat well

Chlamydial eye infections in cats are usually sporadic, affecting one cat here or there. Symptoms develop within 2-7 days after initial exposure.

The first sign is often a slight watery discharge in one eye. This can spread to both eyes. As the disease progresses, severe swelling and reddening of the conjunctiva may be seen and the discharge changes from watery to a thicker yellowish color. Affected cats may squint or keep their eyes closed almost completely due to the discomfort.

If left untreated, the conjunctivitis can last for six to eight weeks (or longer) and cats may continue to shed the organism for many months.

Chlamydia psittaci has also been found in the lungs, gastrointestinal tract and reproductive tracts of cats.

Some researchers believe that Chlamydia may be a cause of infertility in breeding queens.


Although chlamydial infection is a common cause of conjunctivitis in cats, there are also many other causes of conjunctivitis:

  • Trauma to the eye
  • Irritation caused by foreign material in the eyes
  • Lashes or hairs near the eye may be rubbing on the surface of the eye
  • Herpesvirus
  • Calicivirus

If you suspect Chlamydia, you can confirm its presence with a test. Swabs can be taken from the eyes of affected cats and sent to a special laboratory where a culture can identify the presence of the organism. This is usually a highly reliable way of making a diagnosis.


Chlamydia is bacterial, and responds to a number of different antibiotics. The most common antibiotic used is:

  • Tetracycline ointment or drops in the eyes
  • Oral Tetracycline dosed at 15mg/kg every 8 hours
  • Other antibiotic options include oxytetracycline and chloramphenicol

Because the Chlamydia organism can be present in the body other than just the eyes, oral antibiotics treatment may be recommended in addition to topical therapy. Care has must be taken if treating pregnant cats and young kittens however. Oral Tetracycline given to a cat before it has its permanent teeth can cause the permanent teeth to come in bright yellow color. Tetracycline ointment or drops has no effect on the teeth color. Treatment should be continued for 4 weeks and all cats in the household should be treated, regardless if they are showing any symptoms.


Infection occurs through direct contact between animals. Chlamydia organisms cannot survive for any significant period of time in the environment.

At Risk Cats

  • Chlamydial infections are relatively common in cats, especially in multi-cat households, catteries and shelters.
  • Up to 30% of cases of chronic conjunctivitis may be caused by Chlamydia.
  • Although cats of all ages can be infected, the disease is seen most commonly in young kittens 5 – 12 weeks old.


Chlamydia infections are difficult to eliminate entirely from a cattery because they can cause chronic infections without any apparent clinical signs.

Vaccine Options

A vaccine exists to protect cats against chlamydial conjunctivitis. However, the vaccine does not always prevent infection. And MORE IMPORTANTLY, while the vaccine can be helpful in preventing severe clinical disease, giving a cat the Chlamydia vaccine involves considerable risks.

Vaccines containing killed or modified live chlamydia cause 70% of vaccine reactions.

The AAFP has recommended chlamydia vaccines only be given to “high risk” cats, because of the potential for negative side effects from the vaccine.

Human Risk

The well-known Chlamydia that causes sexually transmitted disease (STD) in people is not the same Chlamydia that causes conjunctivitis in cats. They are two entirely different strains of Chlamydia. There have been one or two reports that have suggested human conjunctivitis has occurred following contact with a cat harboring C. psittaci, but the risk appears to be extremely low.

Always practice good hygiene when treating or handling a sick cat. If your cat has conjunctivitis definitely keep your fingers away from your eyes after touching your cat. If you do contract conjunctivitis after treating a cat with chlamydia, mention it your doctor.

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Genetically, just a single gene is the difference in coat color between a kitten that is a brown tabby and its black sibling. The AGOUTI gene is responsible for all tabby coat patterns in cats.