Chlamydial infections in animals
Equine infections
Horses appear relatively resistant to
chlamydial infections, although there have been limited reports of chlamydial-associated
equine disease from Russia, Germany the UK, Australia and Japan. The true extent
of chlamydial equine disease may be under-recognized. In the 1960s, chlamydial agents were recovered from the blood of young foals affected with
bronchopneumonia (Popovici and
Hiastru, 1968). Chlamydiae were also isolated from the brains of horses and mules affected with a
hepato-encephalopathy syndrome (Blanco,
1968). Antibodies to Chlamydia were detected in horses by Studdert
(1969).
Subsequently, chlamydial polyarthritis was diagnosed in an affected foal by
McChesney et al.,
(1974) and chlamydiae were implicated, but not isolated, in cases of equine eye
infection (Storz, 1971). Chlamydial infection was also identified in some respiratory disease cases
(Moorthy and Spradbrow, 1978), from which 2 strains were isolated from the nasal tract. These strains were non-pathogenic to mice and guinea pigs.
McChesney et al. (1982) isolated what was then termed C. psittaci from the lung tisssue of a mare with fatal respiratory disease.
On inoculation into ponies this induced an interstitial pneumonia. C. psittaci was also recovered from the respiratory tract and
conjunctivae of affected thoroughbred horses (Burrell et al.,
1986) and from the genital tract of mares with cervicitis (Krauss et al.,
1988). Furthermore, there was evidence that chlamydial infection might cause
abortion (Glavits et al.,
1988).Giemsa staining impression smears of infected mucosal surfaces / tissues from horses
were considered a rapid method for the presumptive diagnosis of chlamydial
infections Dilbeck et al., (1986).
Wills et al.,
(1990), isolated a chlamydial agent from a horse with a nasal discharge.
This isolate alled N16, grew slowly in tissue culture, contained a unique extrachromosomal
plasmid and was subsequently found to be C. pneumoniae
strain genetically and serologically
distinct from the C. pneumoniae human biovar (Storey et al.,
1993).
However, challenge with the N16 isolate did not produce clinical disease in horses
(Mair and Wills, 1992).
Chlamydial isolates were also recovered in nasal and conjunctival swabs from 15 of 300
horses; one of which also failed to produce clinical disease in ponies.
Moreover, no association between the isolation of chlamydiae and clinical signs of ocular and respiratory disease
in horses was found. C. pneumoniae N16 is considered the type strain of the equine biovar of Chlamydophila pneumoniae.
A serological survey of chlamydial infection in light
horses in Japan was performed by Miyamoto et al.,
(1993). The highest prevalence of chlamydial infections was found in 2-5 year-old light
horses but the chlamydial species involved was not identified.
There is evidence other chlamydiae
may cause infections in horses. In one report, Chlamydophila psittaci was isolated from the aborted foetus of a mare
with respiratory disease and fever during the ninth month of pregnancy. The
identification of C. psittaci was confirmed by PCR tests on the aborted
placenta. This infection probably was acquired from an avian source (Henning et al.,
2000).
[MEW comment: The
pathogenic role of C. pneumoniae in horses is still uncertain. The role
of chlamydiales in equine disease requires further research].
Bibliography
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