Chlamydia in Felines

Chlamydiosis, cause by Chlamydophila felis, is a common bacterial disease of cats which causes upper respiratory tract disease, conjunctivitis and pneumonia[1]. Because the symptoms of chlamydiosis in cats primarily involves upper respiratory tract disease, it needs to be distinguished form Cat Flu, which has similar presenting symptoms.

C. felis was first isolated from the lung of a cat with naturally occurring pneumonia in the United States in 1942, and since then, has been reported worldwide[2]. Zoonotic infection of humans with C. felis has been reported and up to 50% of stray cats found at cat shelters are seropositive to the disease[3].

Chlamydophila organisms are obligate intracellular bacteria which cannot survive for any significant period of time in the environment, and infections are thought to occur by cats grooming each other or spread during fighting.

The organism has been isolated from the vagina of cats and has been believed to be associated with reproductive failure, though a clear association between infection and reproductive problems has not been demonstrated[4]. Chlamydiosis has also been implicated in cats with infective endocarditis and glomerulonephritis[5].

Clinical signs

Chlamydia infection is relatively common in cats and up to 30% of cases of chronic conjunctivitis may be caused by this organism. However, because the organism does not survive in the environment and requires direct contact between cats to spread, disease is much more commonly seen where larger groups of cats are kept together, such as multi-cat households, catteries and shelters. Although cats of all ages can be infected, disease is seen most commonly in young cats (5 weeks to 9 months of age) with persistent or recurrent infection. Some cats can be infected with both cat flu and Chlamydia.

The most common clinical signs are serous to mucopurulent ocular discharge, chemosis, epiphora, blepharospasm and eyelid swelling. Other signs may be noted, such as fever, submandibular lymph node swelling, sneezing, nasal discharge, anorexia and weight loss. In cats, conjunctivitis due to C. felis is often unilateral and often progresses to bilateral.


Diagnosis can be made on clinical signs but needs to be distinguished against other causes of upper respiratory tract infection such as FHV and FCV, which cause Cat Flu, and Mycoplasma spp. Ideally, vaccine history and retroviral (FeLV/FIV) status should be determined for any patient with chronic mucopurulent rhinitis.

PCR testing of conjunctival swabs is readily available in most laboratories, but accuracy of isolation using this technique is not necessarily accurate due to poor recovery rates[6]


Because Chlamydisosis is rarely fatal in cats, and readily treatable, its incidence is often overlooked by clinicians.

Chlamydophila felis is sensitive to a number of antimicrobial drugs, including doxycycline (50 mg/cat per day for 10-14 days) or Azithromycin (given at 5 – 10mg/kg every 3 days for 4 weeks)[7].

Vaccines are currently available with proven efficacy but poor potency. They are effective against eradication of clinical signs, but not clearance of bacteria from the cat. Vaccines are recommended primarily for diagnosed outbreaks in catteries, and not individual cases as antimicrobial therapy are usually effective, and vaccines do not eliminate ‘carrier’ cats from shedding bacteria[8].


↑ Masubuchi, K et al (2010) Efficacy of a new inactivated Chlamydophila felis vaccine in experimentally-infected cats. JFMS 12:609-613
↑ Baker, JA (1942) A virus obtained from a pneumonia of cats and its possible relation to the cause of atypical pneumonia in man. Science 96:475-476
↑ Yan, C et al (2000) Seroepidemiological investigation of feline chlamydiosis in cats and humans in Japan. Microbiol Immunol 44:155-160
↑ Gaskell, RM & Povey, RC (1982) Transmission of feline viral rhinotracheitis. Vet Rec 111:359
↑ Regan, RJ et al (1979) Infective endocarditis with glomerulonephritis associated with cat chlamydia (C. psittaci) infection. Br Heart J 42:349-352
↑ Bonagura, JD & Twedt, DC (2009) Kirk’s current veterinary therapy XIV, Saunders Elsevier, St Louis
↑ Sykes, JE (2005) Feline chlamydiosis. Clin Tech Small Anim Pract 20:129-134
↑ Lappin, MR (2001) Feline internal medicine secrets. Hanley & Belfus, Philadelphia. pp:4-7

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