Comparison of the Polymerase Chain Reaction and Culture for the Detection of Feline Chlamydia psittaci in Untreated and Doxycycline‐Treated Experimentally Infected Cats

Abstract

The diagnostic sensitivity of the polymerase chain reaction (PCR) was compared with that of culture on conjunctival swabs over the course of infection in 4 doxycycline-treated and 4 untreated cats that were experimentally infected with feline Chlamydia psittaci. Treated cats were given 25 mg (5 mg/kg) of doxycycline orally twice daily for 3 weeks from day 6 after challenge. Clinical signs improved within 3 days of institution of treatment. Culture remained positive for 1 day and PCR remained positive for up to 5 days after treatment was commenced. No recurrence of clinical signs occurred and the organism could not be detected by either PCR or culture for 2 weeks after cessation of therapy. In the 4 untreated cats, conjunctival swabs were taken daily to day 14 and every 2nd weekday to day 64 after challenge. PCR was significantly more sensitive than culture in untreated cats overall (PCR 85.7%, culture 72.9%, P ഠ 0) and for cats with clinical signs (PCR 89.2%, culture 79.2%, P ϭ .008). PCR and culture had equivalent sensitivity (100%) for cats showing clinical signs in the 1st month of infection, whereas PCR was considerably more sensitive than culture for cats showing clinical signs in the 2nd month (PCR 72.9%, culture 47.9%, P ϭ .028). Organisms were not detected by PCR in blood or any tissue collected from treated or untreated cats at postmortem. Thus, effective treatment of chlamydiosis in cats is possible with much shorter treatment regimens than currently recommended, and PCR is the more sensitive diagnostic method in chronically infected cats.

Occurrence of Chlamydiaceae and Chlamydia felis pmp9 Typing in Conjunctival and Rectal Samples of Swiss Stray and Pet Cats

“…These findings support the hypothesis that the faecal-oral route might be an alternative infection pathway for C. felis, like it was suggested for different veterinary and human Chlamydia species [30][31][32][33]. Despite the above-mentioned evidence for this hypothesis, only a few authors have pursued these findings, and further investigation upon rectal shedding in naturally infected cats is necessary to gain insight into the epidemiology of C. felis in the cat population [6,25,34].…”

“…It is primarily a pathogen of the conjunctiva and possibly the nasal epithelium [4,5]. Furthermore, it has also been detected in the reproductive tract as well as in different organs and tissues such as the lungs, tonsils, gastric mucosa, spleen, liver, kidneys, and peritoneum (reviewed in [4,[6][7][8]). The biological significance of these latter findings, however, is unclear.…”

“…These authors hypothesised that primary ocular chlamydiosis may result in persistent infection of the genital as well as the gastrointestinal tract [27]. Later, other authors confirmed the detection of C. felis in the reproductive tract of experimentally and naturally infected cats, but neither the possibility of venereal transmission nor its epidemiological relevance has been clarified yet [6,7,23,28,29]. These findings support the hypothesis that the faecal-oral route might be an alternative infection pathway for C. felis, like it was suggested for different veterinary and human Chlamydia species [30][31][32][33].…”

“…In the past, different methods have been used to investigate chlamydial infections in cats. By comparison, PCR of conjunctival swabs showed higher sensitivity than swab isolation and serology [6,34]. Due to the obligate intracellular nature of Chlamydiaceae, sufficient numbers of host cells must be collected in the sampling process to ensure detection of the pathogen.…”

An investigation on the presence of Chlamydiaceae in Swedish dogs

“…In cats there is also circumstantial evidence for a role of Chlamydiaceae in reproductive disturbances, and chlamydiae have been isolated from the vagina of cats, e.g. [4]. Bacteria belonging to the family Chlamydiaceae are also common ocular pathogens, for instance in humans (C. trachomatis) , koalas (Cp.…”