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Chlamydia pecorum:
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Introduction
- Experimental Infection of Laboratory Animals - Immunochemistry - Diagnosis - References |
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Chlamydia pecorum:
Before the establishment
of C. pecorum, all of nonhuman mammals-derived Chlamydia have been classified
as C. psittaci, because they were believed to show the same phenotypes
including morphology of inclusions in culture cells, the absence of glycogen
in the inclusions and resistance to sulfadiazine. C. pecorum was differentiated
by Fukushi and Hirai.
C. pecorum currently
consists of bovine, ovine, and swine strains. A type strain is E58 ATCC
VR628, which was isolated from calf brain in 1953. The species name, pecorum,
is derived from the Latin word which means flocks of sheep or herds of
cattle: only bovine- and ovine-derived strains were original members
of C. pecorum. C. pecorum is resistant to sulfadiazine, forms oval
and dense inclusions in culture cells, does not deposit glycogen in inclusions
and shows typical elementary bodies (EB) and reticulate bodies (RB) which
are morphologically identical to those of C psittaci.
Clinical pictures
of C. pecorum infection varied from inapparent to severe infection and
involved mainly the central nervous, respiratory, and digestive systems.
Inapparent or latent infection was common. After recovery from clinical
infection, many animals remained as Chlamydia carriers, excreting the Chlamydia
for a long time. Among apparently healthy cattle, there was a high
incidence of fecal carriers.
Embryonating
hen's eggs and established cell lines are used to cultivate C. pecorum.
Yolk sac is the ordinary route for inoculation to embryonating eggs. Cell
lines for cultivation of C. pecorum include Madine-Derby bovine kidney
(MDBK), HeLa229, and L929 cells. The type strain E58 can grow only
in MDBK cells so far as we examined.
- Experimental Infection of Laboratory Animals:
* Embryonating
hens eggs:
C. pecorum multiplied
in embryonating hen's eggs. C. pecorum inoculated into the yolk sac
killed the chicken embryo in three to eleven days.
* Swine:
In swine, C.
pecorum produces mild illness with fever, inactivity, and reduced appetite
when given intracerebrally, and pneumonitis when given intratracheally.
However, various clinical pictures were observed in natural infections
of swine.
* Guinea pigs:
C. pecorum
has relatively high pathogenicity for guinea pigs. The intraperitoneal
route is effective to evoke fever, loss of body weight, peritonitis, and
swelling of the spleen in the inoculated animals. Intraperitoneal inoculation
with a dose as small as
0.5 ml of 10-8 dilution
of C. pecorum-infected yolk sac elicited CF antibody in the inoculated
animals.
* Mice: .
C. pecorum has
low pathogenicity for mice. By subcutaneous, intraperitoneal, or
intracerebral inoculation of C. pecorum, mice were little affected, although
by intranasal inoculation C. pecorum readily infected mice.
* Pregnant ewes:
Oral infection
did not result in tissue invasion, since all placental and fecal samples
were negative for Chlamydiae. Intravenous infection resulted in placental
infection in 16 of 18 ewes in that Chlamydiae were cultured from placentas
or vaginal swabs. Two ewes bore dead lambs after a shortened gestation
time. There were no significant differences between the weights of the
lambs from the infected groups and those from uninfected control ewes.
Antigen profiles
of C. pecorum recognized by cattle sera, which possessed complement fixation
and/or ELISA antibodies, were investigated by immunoblotting. Six
out of 9 cattle sera reacted with 40, 56-64 and 84 kDa antigens.
These results indicate strong immunogenicity of 56-64 and 84 kDa antigens
in host immune response and possible immunological diversity of MOMP antigen.
Antigens on
EB of C. pecorum were investigated with rabbit antiserum by immunoblotting.
At least 20 antigens were detected in a range of molecular weight 3 to
200 kDa. Their major antigens were 5-7, 16, 39, 56-64, 84 and 86
kDa. The 5 7 kDa antigen was LPS. Intensity of C. pecorum MOMP
on immunoblot was weaker than that of avian C. psittaci even using homologous
antiserum. Specific monoclonal antibodies showed reactlvlty to C.
pecorum MOMP on immunoblot by Tris-dodecyl sulfate polyacrylamide gel electrophoresis
(PAGE) but no reactivity on immunoblot by sodium dodecylsulfate (SDS)-PAGE.
MOMP of C. pecorum seems to be fragile to SDS in contrast to MOMP of avian
C. psittaci which maintains strong antigenicity after SDS treatment and
heating for electrophoresis.
Antigens of
56-64 kDa would be omp2 and groEL because of their molecular weight.
The omp2 and groEL have not been investigated in C. pecorum, although they
have been recently analyzed on other Chlamydia spp. Molecular biological
and immunological analyses could reveal potential roles of omp2 and groEL
for pathogenlclty of C. pecorum.
The diagnosis
of C. pecorum infection is difficult because of the variability of clinical
signs and the wide distribution of latent infection in addition to lack
of appropriate clinical microbiological diagnostic method. Isolation
of chlamydia and its DNA analysis are necessary for establishing a definite
diagnosis. PCR can be applied for identification of C. pecorum.
Serological
diagnosis is still under investigation to find appropriate antigens.
MOMP does not seem to be the best choice because of their diversity and
fragility. DnaK and GroEL can be candidates of diagnostic antigens,
although further analysis must be done for actual application of these
antigens to diagnostic use.
1) Fukushi, H., Ogawa, H., Morikoshi, T., Okuda, Y., Shimakura, S., and Hirai, K. 1985. Chlamydial complement fixing antibodies in cows, horses and pigs from 1980 to 1983. Res. Bull. Fac. Agric. Gifu Univ. 50: 259-263.
2) Fukushi, H., and Hirai, K. 1988. Immunochemical diversity of the major outer membrane protein of avian and mammalian Chlamydia psittaci. J. Clin. Microbiol. 26: 675-680.
3) Fukushi, H., and Hirai, K. 1989. Genetic diversity of avian and mammalian Chlamydia psittaci strains and relation to host origin. J. Bacteriol. 171: 2850-2855.
4) Fukushi, H., and Hirai, K. 1992. Proposal of Chlamydia pecorum sp. nov. for Chlamydia strains derived from ruminants. Int. J. Syst. Bacteriol. 42: 306-308.
5) Philips,
H., and Clarkson, M. Experimental infection of pregnant ewes with Chlamydia
pecorum. Infection and Immunity, June 1998, p.2818-2821. Vol.66. No.6.
