- Bacterioscopic examination: This is an analysis that enables C. abortus to be demonstrated in non-specialist laboratories. These analyses include those traditional differential stains, such as Stamp’s (Figure 3A) or May-Grünwald-Giemsa (Figure 3B), or more recently direct immunofluorescence (Figure 3D) or immunoenzymatic techniques (Figure 3C) for antigen detection, which are more specific and sensitive if monoclonal antibodies are used. These techniques are performed on cotyledon or vaginal swabs, and are less sensitive when carried out from foetal organs. The cotyledon samples may also be fixed in formalin and included in paraffin for the conduct of immunocytochemical techniques on histological sections.
- Culture: Given the obligate intracellular microorganism character, the use of living cells is required for its culture. The first method used to cultivate chlamydia used the yolk sacks of chicken embryos, which continue to be used routinely in many laboratories. However, the development of the culture methods on cellular lines has moved considerably to embryonic eggs. The most used sensitive cell lines are the McCoy, Vero, HeLa 229 or fibroblast L-cells.
- Molecular techniques: The possibilities of rapid and precise detection of chlamydia on clinical samples have greatly improved since the introduction of molecular methods, particularly gene amplification techniques (PCR), which can be conducted on the same samples, both fresh and frozen, or even on samples fixed in formalin. Unlike conventional PCR, real-time PCR allows for the quantification of the quantity of chlamydia there is in the sample.
Therefore, PCR is a rapid and precise direct technique
3. Indirect or serological diagnosis
The serological diagnosis of OEA is complex due to many factors, but especially due to the latent nature of the infection, which means that seroconversion does not occur until after the abortion.
Furthermore, ruminants are also often infected by C. pecorum, in many cases sub-clinically, but inducing the production of low, but detectable, quantities of antibodies.
For these reasons, this serological diagnosis must imperatively be a group or flock diagnosis.
It is considered that the flock is affected by a latent (or recently vaccinated) infection when we see rates of antibodies equal to or slightly higher than the positivity threshold of the techniques used, considering a flock supposedly exempt when all the serums studied have provided results lower than the established threshold.
The most used methods are the following:
- Complement Fixation Test (CFT): For over 50 years, CFT has been the most used technique for the serological diagnosis of OEA, and is also recommended by the World Organisation for Animal Health (OIE). However, CFT lacks specificity due to the fact that the antigen used mainly consists of lipopolysaccharide (LPS), which is common to all species of the Chlamydiaceae family, making cross-reactions with the antibodies produced against C. pecorum common.
- ELISA-type immunoenzymatic techniques: This is the most used technique at present. It is essential to use commercial kits that use specific recombinant antigens of C. abortus related to the 80-90 kDa POMP-based ELISA, ruling out those that use complete elemental bodies or LPS, since they can give rise to cross-reactions with the responses induced by C. pecorum.
The indirect technique of choice is ELISA
Control & Prevention
There are three types of measures in the prevention and control of OEA:
- General measures related to management, similar to those of any abortive process.
- Treatment with antibiotics, such as tetracyclines, after an outbreak of abortions.
- Vaccinal prophylaxis, with two types of vaccines available at present; attenuated live vaccines and inactivated vaccines.