The Genus Chlamydophila

Chlamydophila psittaci

C. psittaci primarily infects birds. The former 'mammalian' Chlamydia psittaci abortion, feline and guinea-pig strains have been moved to three new species [see: C. abortus, C. felis, C.caviae below]. C. psittaci in birds is often systemic and infections can be inapparent, severe, acute or chronic with intermittent shedding. Most organs become infected, as well as the conjunctiva, respiratory system and gastrointestinal tract. It can also be passed in the eggs. Stress will commonly trigger onset of severe symptoms, resulting in rapid deterioration and death. C. psittaci strains are similar in virulence, grow readily in cell culture, have 16S-rRNA genes that differ by < 0.8%, and belong to eight known serovars. All should be considered to be readily transmissible to humans.

C. psittaci serovar A is endemic among psittacine birds and has caused sporadic zoonotic disease in humans, other mammals and tortoises [see: C. psittaci infections in birds]. Infection is often systemic in birds and can be inapparent, severe, acute or chronic with intermittent shedding. Serovar B is endemic among pigeons, has been isolated from turkeys, and has also been identified as the cause of abortion in a dairy herd. Serovars C and D are occupational hazards for slaughterhouse workers and for people in contact with birds. Serovar E isolates (known as Cal-10, MP or MN) have been obtained from a variety of avian hosts worldwide and, although they were associated with the 1920s–1930s outbreak in humans, a specific reservoir for serovar E has not been identified. The M56 and WC serovars were isolated during outbreaks in mammals. Several other monoclonal serotyping systems have been developed, but a comparative study of these systems has not been done. Several C. psittaci strains have an extrachromosomal plasmid. Many C. psittaci strains are susceptible to bacteriophages.

Chlamydophila pneumoniae

The proposal to establish two genera in the family Chlamydiaceae necessitated transfer of the species C. pneumoniae to the species C. pneumoniae. C. pneumoniae was formerly thought to be a specific human pathogen, but it is now thought to infect horses, koala and other animals [see: veterinary infections]. C. pneumoniae has a genome of approximately 1.2 megabases [see: genome]. In humans, C. pneumoniae is primarily a pathogen of the respiratory tract, causing acute or chronic bronchitis and pneumonia. It has also been associated with obstructive pulmonary disease, atherosclerosis, Alzheimer’s disease, and other acute and chronic respiratory diseases [see: C. pneumoniae infections index]. Chlamydiae belonging to the Koala biovar of C. pneumoniae have been identified in all five Australian free-ranging koala populations that have been tested, including a colony that was suffering from respiratory disease [see: Chlamydial infections in koala]. Isolates are commonly obtained from ocular and urogenital sites, where they do not appear to be highly pathogenic. The equine biovar of C. pneumoniae currently includes only strain N16, which was isolated from the respiratory tract of a horse. N16 has a plasmid while other Ch. pneumoniae do not. Inoculation of horses with N16 leads to asymptomatic infections.

Chlamydophila pecorum

The species Chlamydia pecorum has been renamed Chlamydophila pecorum. C. pecorum strains are generally non-invasive in a mouse model of virulence and are serologically and pathogenically diverse, having been isolated only from mammals: cattle, sheep and goats (ruminants), koalas (marsupials), and swine. In the koala, C. pecorum causes reproductive disease, infertility and urinary tract disease. In other animals, C. pecorum has been associated with abortion, conjunctivitis, encephalomyelitis, enteritis, pneumonia and polyarthritis.

Chlamydophila felis , including feline isolates previously belonging to Chlamydia psittaci

C. felis is endemic among house cats worldwide, primarily causing inflammation of feline conjunctiva, rhinitis and respiratory problems. It can be recovered from the stomach and reproductive tract. Zoonotic infection of humans with C. felis has been reported. Strains FP Pring and FP Cello have an extrachromosomal plasmid, whereas the FP Baker strain does not. FP Cello produces lethal disease in mice, whereas the FP Baker does not. An attenuated FP Baker strain is used as a live vaccine for cats.

Chlamydophila caviae , including guinea-pig inclusion conjunctivitis isolates previously belonging to Chlamydia psittaci

C. caviae can be recovered from the conjunctiva of guinea-pigs suffering from ocular inflammation and eye discharge [see: infection in guinea pigs]. There are five known Ch. caviae isolates, and the ompA (omp1) sequences of these isolates are virtually identical. The strain GPIC contains an extrachromosomal plasmid, pCpGP1. C. caviae infects primarily the mucosal epithelium and is not invasive. The natural site of C. caviae infection is the conjunctiva, but it is possible to infect the genital tract of guinea-pigs with C. caviae and elicit a disease that is very similar to human C. trachomatis infection. C. caviae is markedly specific for guinea-pigs, as attempts to infect mice, hamsters, rabbits and gerbils have been unsuccessful, except for one experimentally infected gerbil.

Chlamydophila abortus , including abortion isolates previously belonging to Chlamydia psittaci

C. abortus strains are endemic among ruminants and efficiently colonize the placenta [see: veterinary infections]. They have a distinctive serotype and nearly 100% conservation of ribosomal and ompA sequences. C. abortus is the reference strain for determining whether a new strain belongs to the Chlamydiaceae (16S- or 23S-rRNA should be > 90% identical to the C. abortus genes). An extrachromosomal plasmid has not been identified in any strain of C. abortus. C. abortus is primarily associated with cases of abortion and weak neonates. Sporadic zoonotic abortion due to C. abortus has been confirmed by genetic analysis of isolates from women who work with sheep [see: C. abortus human infections]. Typical isolates have been obtained from cases of abortion in sheep, cattle and goats worldwide (e.g. strains B577, EBA, OSP, S26/3 and A22). 

[KDE & MEW] May 2002

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