Discussion

History:
Following the emergence of the new equine venereal disease Contagious Equine Metritis (CEM) in Newmarket in 1977 (Crowhurst et al. 1979), the causal organism was found to be a new, Gram-negative, microaerophilic coccobacillus (Taylor et al. 1978), eventually named Taylorella equigenitalis. The Horserace Betting Levy Board (HBLB) developed their voluntary Code of Practice for the control of CEM and these have been updated annually (HBLB 2012). This was adopted by the Thoroughbred breeding industry and some other horse breeders with great success and the disease was eradicated in UK. The UK has remained free of CEM in the horse breeding population until April 2012 when the organism was isolated from 2 mares and a non-Thoroughbred stallion in Gloucestershire (Ricketts et al. 2012). These isolations confirm the continual threat of imported CEM to the UK equine industries and the continuing need for vigilance and efficient diagnosis.

Diagnosis:
Experience confirms that thorough and properly targeted swabbing techniques are vital for the harvesting of reliable diagnostic material for laboratory investigation (Ricketts 1996). For mares, endometrial swabs collected during early oestrus and vaginal discharge screen for acute cases of CEM, whereas narrow- tipped paediatric-type swabs collected from the central clitoral fossa and the clitoral fossa screen for carriers. For stallions, swabs collected from the penile urethra, urethral fossa and diverticulum, prepuce and pre-ejaculatory fluid screen for carriers. Stallions do not become acutely infected with CEM. Immediately following collection, all swabs must be placed into Amies charcoal transport medium and transported to an experienced and adequately equipped laboratory to arrive within 48 h of sampling can identify nonviable T. equigenitalis DNA in swab samples that have been collected adequately but delayed in transport, leading to a 'false negative' culture result.
The qPCR test can differentiate between T. equigenitalis and Taylorella asinigenitalis (the donkey pathogen) and between other organisms, e.g. Oligella urethralis, which may appear similar on gross appearance and biochemical un-reactivity, and may give positive slide agglutination test results.
The qPCR cannot differentiate between viable and nonviable T.equigenitalis DNA so a positive qPCR result should always be followed-up with conventional culture, which will take at least 3 days.

Conclusions:
A negative qPCR test result is reliable for routine industry screening (it is not yet accepted for horse export purposes) but veterinary surgeons are advised to make sure that this is acceptable to the stallion stud manager before sending mares away to stud or 'walking them in' for covering. A multiplex qPCR test is now available for the simultaneous identification of T. equigenitalis, Klebsiella pneumoniae and Pseudomonas aeruginosa, the 3 recognised true equine venereal disease pathogens. On the basis of the results of another similar large- scale field trial (Cash et al. 2012 - unpublished data), this test has also been recognised by the HBLB for it Codes of Practice.
Positive qPCR results will be officially reported to AHVLA and will be confirmed by conventional culture of the viable organism.
Laboratory diagnosis is now based upon the specific culture of viable organisms and/or the detection of its specific DNA by qPCR. Culture of the organism can often be confirmed after 3 - 4 days culture but confirmation of a negative culture takes 7 days. Detection of specific DNA by qPCR can usually be confirmed or ruled out within 12 h of receipt of a sample by an experienced and adequately equipped laboratory. Positive qPCR results are usually repeated before being reported and low signal strength results may require re-swabbing and re-testing.
CEM is a notifiable disease in UK and a suspected positive culture or qPCR result must be reported to AHVLA, who will then confirm or deny the diagnosis and, if positive, will investigate and restrict the movements of the horses involved (HBLB 2012).
Culture, qPCR or both?
The qPCR test has made it possible for busy studfarms to have same-day results for urgent CEM screening of adequately collected and handled swab samples, whereas conventional bacterial culture takes 7 days.