Chlamydia felis (also known as Chlamydophila felis) is a Gram-negative, obligate intracellular bacterium that primarily targets the conjunctiva in cats, making it one of the leading causes of feline conjunctivitis. 

Chlamydia felis infection has historically been referred to as feline pneumonitis, although the organism rarely causes pneumonia in cats. Respiratory involvement is generally secondary and mild, occurring only occasionally alongside ocular disease.

Affected cats most often develop persistent conjunctivitis, marked by red, swollen eyes with discharge, and some cats also show mild upper respiratory signs such as sneezing and nasal discharge.

Although Chlamydia felis infection is less common than some other feline diseases, it remains an important cause of conjunctivitis and upper respiratory signs in cats. 

How It Spreads

Chlamydia infection in cats spreads through direct or close contact with infected cats. The infection spreads through bodily fluids, especially ocular secretions, which play a key role in transmitting feline chlamydiosis (feline pneumonitis). 

Who is at higher risk? Kittens under one year of age are most vulnerable, with the highest prevalence reported in cats between roughly 2 and 6 months old. Kittens are usually protected by maternal antibodies for their first one to two months of life and typically become susceptible, often picking up infection through close contact with an infected queen or littermates, once that protection wanes. Cats living in multi-cat households, shelters, or catteries are at increased risk due to closer, more sustained contact between animals.

Although the zoonotic risk is considered low, occasional human infections have been reported following close contact with infected cats, including handling infected cats or exposure to contaminated ocular and nasal secretions.  

Chlamydia felis Infection Symptoms

Clinical signs typically peak around 9 to 13 days after onset and then gradually subside over the following 2 to 3 weeks. In some cases, symptoms may last for several weeks despite therapy, and recurrence is frequently observed. Untreated cats may continue to shed the bacterium and transmit infection to other cats for several months following the initial episode. 

Symptoms of chlamydia in cats include the following: 

• Transient fever
• Lack of appetite
• Clear or colored ocular discharge
• Redness and swelling of one or both eyes 
• Nasal discharge
• Sneezing
• Mild weight loss

Note that most cats remain clinically stable and continue normal food intake. However, in severe cases of conjunctivitis, cats may present with marked hyperemia of the nictitating membrane, blepharospasm, and ocular discomfort. 

Symptoms in people: Reported signs in people primarily include conjunctivitis, eye irritation, watery eyes, and ocular discharge.