Chlamydia in cats is caused by the bacterium Chlamydophila felis. This pathogen typically leads to a chronic conjunctivitis with clear to mucous eye discharge. When combined with other viral and bacterial agents, chlamydia also contributes to the cat flu complex, which, alongside conjunctivitis, is characterised by coughing, fever and sneezing. As the bacterium has zoonotic potential, we pet owners can also contract chlamydia.
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Learn how to identify the signs of chlamydia in cats and how to support their recovery
Chlamydophila felis is an obligate intracellular bacterium. This means it depends on the cells of the host cat. Outside these host cells, it can only survive briefly. Generally, these host cells are epithelial cells, which are the layer covering the conjunctiva. A unique feature of Chlamydophila felis is its two-part developmental cycle, distinguished by two morphological forms:
Chlamydophila felis is transmitted either through direct contact with contaminated eye discharge or indirect contact with respiratory secretions. Cats can infect each other via droplet transmission. There are also instances of infection transmission between humans and cats. Infected cats shed the infectious stage (elementary bodies) for up to 60 days. However, because elementary bodies can’t survive long outside epithelial cells, they die quickly in the environment. In households with numerous cats, such as in animal shelters or breeding facilities, recurrent chlamydia cases are common.
Some cats can harbour the bacteria for an extended period without symptoms, known as persistence. If the immune system is weakened by stress, other infections (e.g., FIV, FeLV)) or underlying illnesses, the bacteria can reactivate and cause clinical signs.
A classic sign of chlamydia infection is chronic unilateral or bilateral conjunctivitis, characterised by redness, possible swelling of the conjunctiva and eye discharge. This discharge can range from clear to mucous, and in cases of secondary bacterial infections, even pus-like. Severe and untreated infections can lead to significant eye damage, including blindness.
Chlamydophila felis also participates in the cat flu complex, which involves viral agents like Feline Herpesvirus 1 (FHV-1), Feline Calicivirus, Reovirus and Parainfluenza viruses, as well as bacterial agents like Mycoplasma or Bordetella. The cat flu complex presents the following symptoms:
Conjunctivitis is not uncommon in cats. Besides chlamydia, it can result from drafts, smoke or minor injuries. If conjunctivitis doesn’t heal or recurs, a visit to the vet is advisable for eye protection. Before any examination, the vet will gather important background details (anamnesis), such as the cat’s vaccination status, living conditions and diet. If inadequate vaccination protection is noted, the following diagnostic steps are recommended:
A conjunctival swab can confirm chlamydia in a lab through special staining (Giemsa) or molecular biology techniques (e.g., Polymerase Chain Reaction, PCR). Alternatively, antibody levels in the blood can be measured, although this only works if the cat wasn’t previously vaccinated against chlamydia. For accurate results, it’s advisable to repeatedly check antibody levels.
Suspected infections with other agents of the cat flu complex can also be identified via various cultural and molecular methods in the lab. Since many vet practices aren’t specialised in such laboratory diagnostics, it generally takes about 1 to 3 days for a definitive diagnosis.
Though chlamydia resembles viruses due to its intracellular life, it can be treated with antibacterial agents. Antibiotic eye ointments (e.g., tetracycline) or systemic antibiotics in tablet form can be used for severe cases. Cortisone-containing eye ointments also help combat conjunctivitis but are contra-indicated if a corneal ulcer, often seen with Feline Herpesvirus 1 infections, is present.
Chlamydia infection in cats is generally treatable with medication. It’s crucial to see a vet early to prevent potential eye damage and reinfection of other cats. Given the bacterium’s zoonotic potential, humans, especially those with weakened immunity, pregnant women and children, should handle infected cats with care.
Cats in the UK can be vaccinated against chlamydia, but the vaccines only prevent symptoms, not the infection itself. It’s essential to treat a cat with chlamydia and observe proper hygiene measures.
At the Justus-Liebig-University of Giessen I was extensively trained as a veterinarian and was able to gain experience in various fields such as small animal, large animal and exotic animal medicine as well as pharmacology, pathology and food hygiene. Since then, I have been working not only as a veterinary author, but also on my scientifically driven dissertation. My goal is to better protect animals from pathogenic bacterial organisms in the future. Besides my veterinary knowledge, I also share my own experiences as a happy dog owner and can thus understand and enlighten fears and problems as well as other important questions about animal health.
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