Chlamydiaceae

The genus Chlamydia was divided into two genera in 1999: Chlamydia and Chlamydophila. The organisms are Gram negative. Chlamydial or Chlamydiae-like infections occur in an enormously diverse range of animal species, from the amoeba and Hydra through arthropods, insects, mollusks, marsupials, birds, reptiles and mammals to humans. 

At MDS a polymerase chain reaction (PCR) test to detect chlamydial DNA in appropriate clinical samples is performed routinely. Other methods such as direct immunofluorescence of smears, ELISA and cell culture are also available. 

Chlamydial Diseases of different species of animals

Chlamydiaceae Classifications

Chlamydia trachomatis
C. trachomatis is comprised of two human biovars: the trachoma and lymphogranuloma venereum (LGV).

Serovars in both C. trachomatis biovars cause trachoma, sexually transmitted disease, some forms of arthritis, and neonatal inclusion conjunctivitis and pneumonia. The trachoma biovar currently has 14 serovars and infection is limited primarily to epithelial cells of mucous membranes.

The LGV biovar consists of four serovars, L1, L2, L2a and L3, which can invade lymphatic tissue.

C. trachomatis strains are generally sensitive to sulfadiazine and tetracyclines.

Most strains of C. trachomatis are recognized by monoclonal antibodies to epitopes in the VS4 region of MOMP. However these may also cross-react with C. suis or C. muridarum.

Chlamydia muridarum
C. muridarum is a new species created out of the former mouse pneumonitis biovar of C. trachomatis, which has long been known.

Two strains of C. muridarum, MoPn and SFPD have been isolated from mice and hamsters. MoPn infection may be asymptomatic or produce pneumonia in mice. SFPD is an enteric isolate and was obtained concurrently with a causative agent of proliferative ileitis. MoPn is sensitive to sulfadiazine.

The main interest in this species is its ability to establish experimental infections in mice that, to some extent, mimic C. trachomatis infections in humans. Inoculation of C. muridarum into the vagina of mice can give rise to both lower and upper genital tract infection. In the latter case, as in humans, infertility may arise as a result of bilateral scarring of the oviducts.

Chlamydia suis
C. suis has only been isolated from swine, where it causes conjunctivitis, enteritis, pneumonia, and a high incidence of apparently asymptomatic infection. Some strains are resistant to sulfadiazine and/or tetracycline.

Chlamydial infections in pigs have been described as the cause of several different clinical syndromes including pneumonia, conjunctivitis, polyarthritis, and polyserositis. In addition, infection has also been associated with reproductive disorders, notably abortion in sows and orchitis in boars. The distribution of chlamydial infections of pigs appears to be worldwide, the majority probably occurring in large breeding complexes.

Although antibiotic resistance has been uncommon among chlamydiae, two C. suis strains are resistant to tetracycline, one of the main planks of anti-chlamydial chemotherapy have been reported.

C. suis serves as an experimental model of genital C. trachomatis infection. Female reproductive hormones influence chlamydial infection both in vivo and in vitro. Given the reduced availability of human genital tissues for research purposes, female swine genital epithelial cells have been described as a relevant alternative cellular model.

The possible presence of mixed chlamydial infections involving up to three chlamydial species causing both symptomatic and inapparent infection is an important consideration for the xenotransplantation of pig organs to humans. Although specific pathogen-free pigs may be used for this purpose, screening methods will need to cover chlamydiae in order to eliminate the possibility of zoonotic infection. 

Chlamydophila pecorum
Chlamydial strains previously designated Chlamydia pecorum have been reclassified as Chlamydophila pecorum and are associated with infections in mammals including cattle, sheep and goats, koala and swine. C. pecorum strains are associated with pneumonia, polyarthritis, conjunctivitis, abortion, encephalomyelitis, enteritis and diarrhea. They may also cause metritis, salpingitis and infertility in cattle. In koalas, infection with C. pecorum causes genito-urinary disease. The shedding of infectious chlamydiae in feces is likely an important means by which infections are spread in animals. Stressing of carrier animals may precipitate chlamydial shedding and the onset of overt disease.

Serological evidence of chlamydial infection was also reported in antelope and in captive Arabian oryx). Chlamydiae were also isolated from fur seals, while systemic infection with chlamydiae have led to major mortalities in snowshoe hares and muskrats.

Chlamydophila caviae
Guinea pigs with primary conjunctivitis develop immunity to reinfection of the eyes or the genital tract.

The guinea pig is an important experimental model of chlamydial genital tract infection in humans. 

Chlamydophila felis
Feline chlamydiosis caused by strains of Chlamydophila felis is associated with pneumonia and conjunctivitis in cats. The disease is highly debilitating and contagious. C. felis infection is frequently referred to as feline pneumonitis.

Chlamydophila abortus
Chlamydophila abortus is a cause of abortion and fetal loss in ruminants (sheep, cattle and goats). Infection with strains of this microorganism has also been associated with abortion and other clinical symptoms in humans. Chlamydial abortion in sheep is also known as ovine enzootic abortion (OEA) or enzootic abortion of ewes (EAE).

Chlamydophila psittaci
Chlamydophila psittaci infections occur in a wide range of domesticated and wild bird species. Strains of the organism are very common among avian species, with world-wide recognition of these infections. It is likely that all avian species may be natural hosts for C. psittaci. A common sign of chlamydial infection in many birds is conjunctivitis or keratoconjunctivitis. In parrots, parakeets and other cage birds, acute disease is characterized by diarrhea, anorexia and droopiness. In racing pigeons, respiratory signs such as rhinitis, bronchitis and inflammation of the air sac predominate. In C. psittaci infections of ducks, serous or pussy nasal and ocular discharges are typical, resulting in encrusted eyes and nostrils. Early signs of disease in avian species may include respiratory signs such as dyspnea, rales, coryza and sinusitis, unilateral conjunctivitis, diarrhea and polyuria. In the acute phase of infection, further signs may be apparent, such as reduced body temperature, lethargy, loss of appetite, weight loss, dehydration, ruffled plumage and the voiding of greenish-yellow gelatinous droppings. Egg production is reduced.

Chlamydial infections in other animals
Among mammals, chlamydiae have been isolated from rabbits, ferrets and opossums. In rabbits chlamydiae cause spontaneous abortion and pneumonia. Many strains and colonies of mice are inapparently infected with chlamydial agents. Isolates were recovered from the lungs of clinically normal mice. Chlamydial strains have also been isolated from seemingly healthy wild rodents.

There are a number of reports of chlamydial infections in buffaloes. Serological surveys suggest that chlamydial infections occur in a large range of mammals including monkeys, wild boar and hedgehogs; deer and reindeer, fallow deer, mouflon, red deer and Spanish ibex. These species apparently acted as reservoirs of chlamydial infection; transmission between wild and domestic ruminants (sheep and goats) occurred through grazing on the same pastures.

Reptiles
There are a number of reports of chlamydial infection and disease in reptiles. In chameleon species, a lizard was reported with Chlamydia-like organisms in inclusions in macrophages from the spleen and liver. Chlamydia were responsible for moderate levels of death among farmed green sea turtles. Clinical signs included lethargy, anorexia and an inability to dive. Post-mortem showed necrotizing myocarditis, as well as sub-acute pneumonia and chronic or active enteritis. A disease syndrome in farmed, hatchling Nile crocodiles, consisting of acute hepatitis and edema, is caused by C. psittaci.

Amphibians
PCR studies indicate that a pneumonia and anemia disease syndrome in wild giant barred frogs in Australia is probably caused by the koala biovar of Chlamydophila pneumoniae. This was thought by the authors to be the first report of a chlamydial strain infecting both warm and cold blooded host. The giant barred frog has the distinction of being the fourth known host for C. pneumoniae, in addition to humans, koalas and horses. Chlamydial infections have also been described in another amphibian species, the African clawed frog.

Fish
The agent causing epitheliocystis disease of the gills in fish is considered to be Chlamydia or a Chlamydia-like organism. Chlamydial infections cause chronic gill disease in many species of fish.