Chlamydia suis
See also: Infections in pigs
In the old Page classification, the former C.
trachomatis was considered to consist of three biovars, based on host or tissue
specificity. These were the LGV biovar (lymphogranuloma venereum in humans); the
TRIC biovar (oculo genital infections in man, serovars D to K) and the mouse
pneumonitis biovar (infections in mice which have long been known; now
reclassified as C. muridarum). However, in 1994 a chlamydial isolate designated S45 was
identified in apparently healthy pigs. This was quite different to the other
chlamydiae [Chlamydophila species] causing infections in pigs, as it had characteristics resembling Chlamydia
trachomatis (Storz et al., 1994). Thus S45 was sulfadiazine sensitive, as C. trachomatis generally
is. Sequencing studies on the gene
encoding the major outer membrane protein indicated that this isolate was closer
to the mouse biovar of C. trachomatis [now C. muridarum] than to
the C. trachomatis biovars naturally infecting humans. Initially regarded as a separate porcine biovar of C. trachomatis,
it seems likely that infections
with S45-like organisms in pigs may be relatively widespread and
under-diagnosed (Storz et al.,
1994). Given differences in host tropism and in the sequence of the gene
encoding 16S rRNA, these strains have now been officially reclassified as Chlamydia suis (Everett et al.,
1999). In experimental infections in gnotobiotic pigs, C. suis
strains caused asymptomatic intestinal infections in young weanling pigs, with
intestinal lesions but no diarrhoea (Rogers
and Andersen, 2000). Intestinal chlamydial infections have also been
associated with the development of a multi-system wasting syndrome in
post-weaning pigs (Carrasco et al., 2000). The suspicion of
Storz et al., 1994 that C. suis might
be quite common was confirmed in a major epidemiological study. The lung and
intestine of 49 pigs with respiratory disease and the cervix of 205 sows with
reproductive disorders were investigated for chlamydial infection by polymerase
chain reaction targeted at the omp1 or omp2 genes. Chlamydial amplicons were
detected in 49.0% of the pigs with respiratory disease and in 60.0% of sows with
reproductive disorders, as well as from the respiratory tract of 24.5% of
healthy pigs, but 0% from the reproductive tract of fertile sows. DNA
hybridisation studies on the porcine lung and intestine samples showed a
high prevalence of mixed infections with Chlamydophila abortus and
Chlamydia suis, confirmed by RFLP and nucleotide sequence. In the genital
tract samples from infertile sows, the majority of the chlamydiae (81.3%) were
identified as Chlamydophila abortus. Nucleotide sequencing on the gene
encoding the major outer membrane protein in C. suis indicated substantial
heterogeneity compared with the reference C. suis S45 strain (maximum homology
82.7%) [Hoelzle et al., 2000].
Given the close relationship of C. suis
to C. trachomatis, it is alarming that, in Nebraska, tetracycline
resistant C. suis strains have emerged [Lennart et al.,
2001]. The
resistant strains could grow in tetracycline up to 4 ug per ml, whereas
sensitive C. suis and most human C. trachomatis are sensitive to
about 0.1 ug per ml. Both C. suis and C. trachomatis were capable
of growing together in the same inclusion.
C. suis model of genital C.
trachomatis infection
Previous studies have demonstrated that 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 [Guseva et al., 2003].
Mature female swine eliminated from breeding programs were considered animals of
choice for this purpose because: a) the similarity of a sexually transmitted
disease syndrome and sequelae in swine to comparable disease in humans; b) the
near identity of Chlamydia suis to Chlamydia trachomatis serovar D
from humans, and c) similarities in pig epithelial cell physiology and mean
length of oestrous cycle to humans. Epithelial cells from the cervix, uterus,
and horns of the uterus were isolated and cultured in vitro in Dulbecco's
minimum essential medium-Hanks' F-12 medium with and without exogenous hormone
supplementation, and infected with Chlamydia suis S-45 infectivity. The
distribution of chlamydial inclusions in swine epithelial cells was uneven and
influenced by the genital tract site chosen and hormone status.
Oestrogen-dominant swine epithelial cells were more susceptible to chlamydial
infection than progesterone-dominant cells. Furthermore, differentiated luminal
epithelial cells were more susceptible to infection than less differentiated
glandular epithelial cells. The latter cell type was characterised by persistent
chlamydial infection. Freshly isolated primary pig epithelial cells frozen at
-80 degrees C with 10% dimethyl sulphoxide were readily resuscitated and formed
characteristic polarized monolayers in 3 to 5 days.
[MEW Comment: These
studies suggests that C. suis is probably a common and widespread
organism in pigs, although information is very limited. The likelihood of mixed
infections makes it difficult to attribute the pathology of the natural
infections to C. suis alone. However the experimental oral infections in
pigs indicate that this organism is probably a significant veterinary pathogen.
The emergence of tetracycline resistant C. suis in Nebraska indicates
that, given widespread tetracycline use to treat human genital tract infections
with C. trachomatis, one should not be complacent about the possibility
of antibiotic resistance emerging in the latter organism. It is important to
establish the genetic and biochemical basis of tetracycline resistance in C.
suis. Given the shortage of human genital tissue for research in many
countries, the observation that C. suis infection of swine genital epithelia can
be used as a model for the effects of genital hormone on chlamydial infection is
important].
[PG & MEW] Updated September 2003
See also:
Infections in pigs
NEXT: Chlamydophila
psittaci
Animal infections
Index
References
Carrasco, L., Seales, J., Bautista, M.J., Gomez-Villamandos, J.C.,
Rosell, C., Ruiz-Villamor, E. and Sierra, M.A., (2000). Intestinal chlamydial infection concurrent with post-weaning multi-systemic wasting syndrome in
pigs. Vet. Rec. 146: 21 - 23.
Everett, K.D., Bush, R. M. and Andersen, A. A., 1999. Emended
description of the order Chlamydiales, proposal of Parachlamydiaceae fam.
Nov. and Simkania fam.nov., each containing one monotypic genus, revised
taxonomy of the family Chlamydiaceae, including a new genus and fire new
species, and standards for the identification of organisms. Int. J. Syst.
Bacteriol. 49: 415-440. 
Guseva, N. V., Knight, S. T., Whittimore, J. D. & Wyrick,
P. B. (2003).
Primary cultures of female swine genital epithelial cells in vitro: a new
approach for the study of hormonal modulation of Chlamydia infection. Infection
and Immunity 71, 700 - 710.
Hoelzle, L. E., Steinhausen, G. & Wittenbrink, M. M.
(2000). PCR-based
detection of chlamydial infection in swine and subsequent PCR-coupled genotyping
of chlamydial omp1-gene amplicons by DNA-hybridization, RFLP-analysis, and
nucleotide sequence analysis. Epidemiol Infect 125,
427 - 439.
Lenart J, Andersen AA, Rockey DD. (2001). Growth and
development of tetracycline-resistant Chlamydia suis. Antimicrobial
Agents and Chemotherapy 2001 Aug;45(8):2198-203.
Rogers, D.G. and Andersen, A.A., (2000). Intestinal lesions caused by a strain of Chlamydia suis in weanling pigs infected at 21 days of
age. J. Vet. Diagn. Invest. 12: 233-239.
Storz, J., Baghian, A. and Kousoulas, K.G., (1994). Advances in detection and differentiation of chlamydiae from animals. In: Chlamydial Infections, Proceedings of the Eighth International Symposium on Human Chlamydial Infections, Orfila J et al.
ed.
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psittaci
Animal infections
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