|Article Index||"Caprine Chlamydiosis"||Article Index|
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Although most of the work on chlamydial infections of small ruminants concerns ewes, chlamydiosis has an economic and public health impact in numerous goat farms throughout the world. Chlamydial abortions were reported for the first time in Germany in 1959.After that the disease was diagnosed in Bulgaria, Spain, USA, France, India, Japan, United Kingdom, Chad, Greece, and Tunisia. In many areas, chlamydial abortion is the second cause of infectious abortions after brucellosis, and the main cause in most of the countries where brucellosis is controlled
Phylogenetic analyses of 16S and 23S rRNA genes suggest the existence of nine differentiated species in the Chlamydiaceae, and lead Everett et al.,  to propose the creation of two new genera Chlamydia and Chlamydophila. The genus Chlamydia, which corresponds to the old Chlamydia trachomatis denomination includes 3 species: C. trachomatis (human strains), C suis (porcine strains related to C. trachomatis isolated from spontaneous abortions, vaginal infections, and pneumoniae) and C. muridarum (mouse-hamster strains).
The genus Chlamydophila regroups 6 species: C. pneumoniae, C. pecorum, C. psittaci (previous Chlamydia psittaci avian strains), C. caviae, the agent of guinea pig inclusion conjunctivitis (GPIC), C. felis (C. psittaci strains that infect cats) and C. abortus (classical serotype-1 Chlamydia psittaci strains). The results are in agreement with those obtained through phylogenetic analyses of five other coding genes (GroEL, KDO-transferase, MOMP, 60-kDa cysteine-rich protein, and cysteine-rich lipoprotein)  and the biological properties of the strains . The restriction length polymorphism analysis (RFLP) of the ribosomal intergenic spacer domain of 16S-23S rRNA genes provides a rapid and reproducible method for identifying and classifying the chlamydial strains in the new species . However, some memebers of the scientific community do not agree with the proposal for a new Chlamydial taxonomy, as it does not take into account the whole genome of the bacteria.
Although we have demonstrated that servicing infected goats could result in infected sires , until now no epiddymitis due to C. psittaci has been described in sires. This is probably due to the very small number of studies on caprine chlamydiosis rather than a greater susceptibility of rams and bulls to chlamydial infections.
In a newly infected flock the rate of abortion is severe. Frequently 30% or more, sometimes 90% of pregnant does may abort and milk production may decrease. The high rate of abortion is observed for 2 or 3 years after which the disease takes on a cyclic nature: 10% of pregnant females will abort every year for several years until a new outbreak occurs and then all the yearlings will abort. The high level of immunity produced after abortion is responsible of the cyclic evolution of the disease in the herd: it is exceptional for a goat to abort twice. Papp and Shewen  have shown that some of the ewes that aborted can become chronically infected. Chlamydial antigens and DNA can be detected in the vagina, uterus and uterine tubes during the peri-ovulatory period of ewes that aborted. No research has been done to determine the incidence of chronic infections in goat herds.
Transmission of the Disease
Young goats born from infected mothers may retain the infection in the herd or transmit it to other herds. The survey of a group of 27 yearlings in an infected herd during their first year of life demonstrated how they could spread the disease by not being detected by their serological response. These young goats could be divided into 3 groups according to gestation/parturition. The first group kidded normally a live kid, the second group was barren or had aborted too early in pregnancy to be detected and in the third group goats had aborted. The complement fixing (CF) antibodies of the two first groups increased to reach a maximum (1/80 - 1/160) at the time of breeding, then antibody levels decreased until the time of kidding . The third group had a CF antibody titer <1/40 which is not considered as significant until the onset of abortions.
The role the venereal transmission of chlamydiosis by males still needs to be investigated. However, genital infections in rams and bulls result in male infertility and sterility rather than abortion in females. The role that the disease plays in inapparent intestinal infection and its influence in the epidemiology of chlamydial abortion needs to be explored. The recent identification of molecular markers for caprine intestinal strains  would allow such studies.
Staining of Chlamydia by the Stamp, Gimenez or Machiavello methods is quick and can be undertaken easily in most laboratories but its interpretation is often tricky as it requires an experienced person to differentiate Chlamydia from Brucella and Coxiella. Immunofluorescence using immunoglobulin conjugates marked with fluorescent labeled isothiocyanate, increases the sensitivity and specificity of the detection of chlamydia in smears or placenta impressions.
The presence of chlamydial antigens in ground placenta or vaginal swabs sampled just after abortion may be detected by ELISA with diagnostic kits developed for human C. trachomatis infections [17,18].
In human medicine, polymerase chain reaction (PCR) or its variation, ligase chain reaction (LCR) are considered to be the most sensitive diagnostic methods available for diagnosis of Chlamydia. Several primers common to all type of Chlamydia, as Omp1, the gene coding for the major outer membrane protein , or specific of C. psittaci  or C. pecorum  or of the serotype-1 C. psittaci strains  have been developed for veterinary application. But this technic remains expensive.
The complement fixation test (CFT) is the most widely used and considered being the gold standard for serological diagnosis. However, CFT is not very sensitive and not specific because the test uses an antigen i common with C. pecorum, which most goats harbor in their intestine. Therefore, positive reactions with titers between 1:10 and 1:40 are not specific for abortion but may relate to an intestinal infection with C. pecorum. The CFT test should preferably be done 3 to 6 weeks after abortion or lambing, when the antibody response is at its maximum level. The CFT test cannot be used for individual diagnosis or to detect infection in young or in males .
Several attempts were undertaken [24-29] to develop more specific techniques, which would distinguish between C. psittaci and C. pecorum infections. However, none of these tests was sufficiently sensitive and specific. Recently, a new indirect enzyme-linked immunosorbent assay (ELISA) based on a recombinant antigen that express a part of a protein of 80 - 90 kDa has been developed [30,31]. The test reacts with serum antibodies  elicited early against these highly immunogenic [33-35] multigenic family proteins . This test has high sensitivity and high specificity .
The role of antibodies in preventing placental and fetal infection by C. psittaci has been demonstrated in mice. Passive transfer of specific polyclonal sera induces significant immunity albeit lower than T cell-mediated protection . Monoclonal antibodies (Mabs) which neutralize C. psittaci infectivity in vitro confer a remarkable immunity to pregnant mice after intravenous challenge since abortion and fetal colonization are eliminated . Humoral immunity is involved in protection. Its effectiveness depends on the concentration of specific antibodies against the appropriate epitope. All protective Mabs isolated to date react with thermosensitive conformational epitopes located on a MOMP oligomer .
Hence, the MOMP oligomer could be a potential vaccine component . It is not feasible, however, to produce this antigen by extraction from chlamydiae as cost of production would vastly exceed that a farmer would consider affordable for a caprine or ovine vaccine. Therefore, alternative methods of vaccine production must be investigated.
The generation of recombinant MOMP oligomer may be difficult. The gene encoding MOMP, Omp1, is well characterized, but high level expression of the full length gene from an unregulated promoter is toxic to E. coli. For this reason, different experimental strategies for the generation of the protective epitopes were undertaken. We tried to mimic the protective epitopes with monoclonal anti-idiotypic antibodies, or conformationally constrained peptide mimotope, but none of them were efficient. We decided to assess the vaccination of mice with DNA vaccine as DNA vaccination with MOMP gene protected mice against C. trachomatis  and turkeys against C. psittaci . Until now only partial protection was obtained but further research (on target gene, concentration of DNA, route of vaccination, etc.) is needed to know whether mice could be protected with a DNA vaccine as efficiently as with live vaccine.
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