Detection of Chlamydophila felis by RT-PCR method

Chlamydia life cycle

Taxonomy

Infection transfer

Infection occurrence

Clinical signs

Diagnostics

Treatment

Vaccination

Chlamydia (Chlamydiae) is an intracellular parasite occurring in humans and many kinds of animals. Chlamydia has not its own ATP system and it uses the ATP of the host cell for its metabolic processes and therefore is also called energy parasite.

Chlamydia life cycle

Chlamydia are characterised by a unique growth cycle which includes an infectious elementary body (EB) and a reticular body (RB). The elementary body is metabolically inactive and does not replicate; it attaches to a susceptible host cell, by which it is taken up by a process similar to receptor-mediated endocytosis. The entire life cycle occurs within a pouch called an endosome. The endosome increases due to the repeated replication and can be seen morphologically in the affected cell as so-called inclusion. After several hours upon entering the cell, the EB transforms into a larger non-infectious, but metabolically active reticular body. The reticular body replicates by binary fission and reorganizes into infectious EBs. The length of the life cycle depends both on the chlamydia strain and the host cell. It usually takes 48-72 hours. The Chlamydia life cycle usually ends by cell lysis or extrusion of infectious elementary bodies. Intact inclusions are sometimes expulsed from the cell by exocytosis, which also takes place during release of infectious bodies in case of chronic infections.

Taxonomy

Former, the family Chlamydiaceae included only one genus Chlamydia with four species: C. trachomatis, C. psittaci, C. pneumoniae and C. pecorum. On the basis of ribosomal RNA-analysis, the system (taxanomy) has been reorganised, some species has been renamed and some C. trachomatis and C. psittaci have been reclassified as new species. Today, the family Chlamydiaceae includes two genera:
    the genus Chlamydia (C.) with classified species C. trachomatis, C. suis and C. muridarum
    the genus Chlamydophila (Ch.) which includes the species Ch. pneumoniae, Ch. psittaci, Ch. abortus, Ch. pecorum, Ch. felis and Ch. caviae.
The genome Ch. felis was sequenced and published in 2006 (Azuma et al. 2006).

Infection transfer

The primary target of Ch. felis is the conjunctiva and the infection is usually associated with conjunctivitis (inflammation of conjunctiva). The presence of Ch. felis is found in up to 30% of cats affected with chronic conjunctivitis. Ch. felis is not able to survive outside the host and the infection transmission requires close contact between the infected animals. The infection transmission by eye secretion represents obviously the most significant way of infection transmission between cats. Infection by conjunctive discharge usually stops approx. within 60 days after infection, but can develop into enduring infection.

Infection occurrence

The infection rate is higher in cats in multicat households, especially in breeding catteries and is more likely in purebred cats. Most cases of infection occur in young cats under 1 year of age. Antibodies against Ch. felis were proven in more than 10% of unvaccinated cats. In 12-20% cats with diagnosis of conjunctivitis or upper respiratory tract infection, the infection caused by Ch. felis was proven by PCR method. The prevalence in healthy cats is low. In cats showing no clinical signs is the prevalence obviously lower than 3% (Di Francesco et al, 2004).

Clinical signs

The incubation period of Ch. felis infection is usually 2-5 days. The signs usually start in one eye, and as the infection progresses, it spreads to both eyes. At the beginning, the discharge is watery; later the discharge becomes thicker and mucoid or mucopurulent. The characteristic feature of chlamydia infection is chemosis (it is an edema or swell of conjunctiva, in typical case the swelling around the cornea looks like half-open shell - chemosis comes from the Greek cheme - shell). There can be intense conjunctivitis with extreme hyperaemia of the nictitating membrane, blepharospasm and ocular discomfort.  Respiratory symptoms are generally minimal and in cats with respiratory disease without eye infection is an infection caused by Ch. felis unlikely. Transient fever, inappetence and weight loss may occur shortly after infection, although most cats remain in good condition and continue to eat.

Diagnostics

The spectrum of diagnostic methods includes a number of techniques for direct proof of infectious agent (e.g. PCR, cultivation methods) and indirect proof by serological methods (e.g. ELISA, proof of antibodies by immunofluorescence). The Genomia laboratory performs direct determination of Chlamydophila felis in a sample by real-time PCR method. It is a highly sensitive and reliable method that detects the presence of DNA of Chlamydophila felis.
To diagnose the infection caused by Chlamydophila felis, ocular swabs are generally used. A correct technique of taking swabs from eyes is very important for examination by PCR method. Since the Chlamydophila felis is an intracelullar microorganism, it is important to obtain conjunctival swabs containing a sufficient number of conjunctiva cells.  Chlamydophila can be also proven in vaginal, rectal swabs, from aborted fetal tissues. These samples are seldom used for diagnostic purposes.

Treatment

The Chlamydophila infection in cats can be effectively treated by antibiotics, while the system antibiotics are more effective than the local application of antibiotics. In case of Chlamydia infections, tetracyclines are generally regarded as the antibiotics of choice. The recommended treatment takes usually at least 4 weeks. Single housing and routine hygiene measures should suffice to avoid cross-infection.

Vaccination

Cats can be vaccinated by multivalent vaccines on the basis of whole Chlamydia organisms. The available vaccines are deactivated or modified live vaccines. The vaccination does not protect directly against infection, but reduces the occurrence of clinical signs. Comparison studies of deactivated and modified live vaccines are not currently available. Vaccination is to be considered if Chlamydia infection occurred in the past. Cats living with other cats should be vaccinated regularly. Kittens are usually vaccinated in the age from 8 to 10 months and the second injection follows 3 to 4 weeks later. For cats with lasting risk of exposure, every-year re-vaccination is recommended.