Chlamydia in Goats

Chlamydia

Clinical Signs

Chlamydiosis is clinically characterized by abortion during the last months of pregnancy, stillbirths or premature births of weak kids with low birthweight. Abortions occur without previous clinical specific signs even if some goats may develop persistent cough without breathlessness, or arthritis and keratoconjunctivitis. In experimental infections, slight vaginal discharge was observed the day before abortion on some goats [8]. Retained placentas and metritis are not usual, even if they are more frequent than in ewes [9]. After the abortion, goats may recover rapidly [10] or may present brown discharge from the vagina. In experimental infections [8] or in some natural infections with a high rate of abortions [11] only 50% or less of goats that aborted, recovered quickly whereas post abortive sickness in ewes is unusual. This could be due to virulence differences between strains since very little is known on virulence mechanisms of strains. No difference in virulence could be shown in mouse models between ovine and caprine strains [12], but amplified fragment length polymorphism (AFLP) revealed genomic differences between caprine strain AC1 and ovine serotype-1 C. psittaci strains [13].

Although we have demonstrated that servicing infected goats could result in infected sires [14], 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 [15] 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.
The fetus does not display specific macroscopic lesion. Kids delivered close to term may be covered by brown material. Clear or blood-stained diffuse edema [16], blood-stained fluids in abdominal and pleural cavities and petechiae on the tongue, in the buccal cavity and on the hooves are often observed.

Transmission of the Disease

Infected does excreted large numbers of Chlamydiae in placenta and fetal fluids at the time of kidding and at the time of abortion. Some goats may shed Chlamydia in vaginal fluids from more than two weeks before abortion to more than two weeks after abortion. This may explain the higher incidence of abortion in newly infected herds of goats, since the susceptibility to infection varies in relation to the physiological status of the animal. Goats that are less than 100 days pregnant are more susceptible than those at the end of gestation or those that are barren. Smaller amounts of Chlamydiae can also be shed in urine, milk and feces during several days after abortion.

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 [13] would allow such studies.

Diagnosis

The diagnosis is usually performed by the detection of bacteria in smears or impression of the placenta combined with serological analysis of at least ten sera samples.

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 [19], or specific of C. psittaci [20] or C. pecorum [21] or of the serotype-1 C. psittaci strains [22] 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 [23].

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 [32] elicited early against these highly immunogenic [33-35] multigenic family proteins [36]. This test has high sensitivity and high specificity [37].

Treatment

Tetracyclines affect the replication of chlamydia and can be effective in preventing abortions. The injection of 20 mg/kg of oxytetracycline given by intramuscular route at 105 and 120 days of pregnancy can prevent abortion but cannot prevent the chlamydial shedding at kidding.

Vaccination
Killed vaccines could reduce the incidence of abortion but not the excretion of Chlamydiae at kidding. Abortion induces a strong enough immunity to withstand later challenges [38], a live vaccine constituted with a temperature sensitive mutant of C. psittaci strains was developed [39]. Susceptible goats were vaccinated before mating [14] and no interference with the subsequent gestation was noted. Goats were protected against chlamydial abortion and chlamydial shedding at kidding was prevented. Nevertheless, when all goats in an infected herd are vaccinated the first year and all replacement animals are vaccinated on subsequent years, it could take about 3 years before abortions stop. This is due to latent infection in goats, goats that were infected before vaccination but had not aborted. Vaccination will not change the course of a latent infection. These goats may abort or may kid healthy or infected kid at term and may or may not shed Chlamydiae. As long as goats with a latent infection are present in a herd, it is not advisable to stop vaccinating (or else abortions would start anew), nor is it possible to sell vaccinated animals, excepted to breeders who vaccinate their flock regularly.