Contagious Equine Metritis (CEM) What is it and How to Treat it?

What is CEM? 

Contagious Equine Metritis is known as CEM. This bacterial venereal disease occurs after a horse becomes infected with Taylorella equigenitalis. CEM is an OIE-listed disease with severe economic and epidemiological considerations for the horse industry.

The bacteria is a gram-negative organism that is sexually transmitted, resulting in chronic infections in mares and subclinical infections in stallions. Horses with chronic CEM are challenging to cure and treat effectively. 

Horse herd

How is Contagious Equine Metritis Transmitted and Diagnosed?

The main transmission route for CEM is through artificial or natural breeding practices. Equipment like halters, semen collectors, or contaminated clothes used in artificial breeding can act as an infection source if poor hygiene protocols are in place. 

The stallions harbor the bacteria on the penis shaft, in the urethral fossa, or within the shmega found in the penis sheath.

Diagnosing CEM requires a thorough physical exam and detailed clinical history; it is also imperative to differentiate between metritis and CEM. The tests used to identify CEM include a bacterial culture or molecular diagnostic testing.

Isolating the causative bacteria is the only way to diagnose CEM precisely. Vets need to take swabs from the following areas in mares:

  1. An endometrial swab, ideally during estrus.
  2. A swab of the clitoral fossa and sinuses.

Stallions show subclinical infections, but if a suspected outbreak becomes linked to a stallion, a vet needs to sample the following areas:

  1. Swabs of the urethral fossa, urethra, prepuce sheath, and the shaft of the penis.
  2. An ejaculate or pre-ejaculatory fluid sample is a requirement for diagnostic sampling.

A vet must test a stallion three times before the stallion is declared CEM-free.

The swabs must travel in Amies transport medium at a temperature of 39,5°F (4°C) or on ice. The sample must arrive at the lab within 24 hours after collection or be frozen if transport takes longer. Ensure that the laboratory is qualified to perform CEM testing. 

The serology tests available do not reliably detect carrier animals. PCR assays detect the Taylorella bacteria, and then bacterial cultures narrow the diagnosis down to either T. equigenitalis or T. asinigenitalis. The bacteria grow slowly and are also tricky to culture. 

The golden standard of testing involves complement fixation tests coupled with three sets of cultures to aid in CEM diagnosis in quarantined mares. It is important to note that recent courses of antibiotics may result in false negative tests. 

Test breeding may be necessary for stallions bred to CEM-negative mares. Once bred, the mares must undergo a complement fixation (CF) test and have swabs taken for cultures. 

Close up head shot of horse

Clinical Symptoms and Signs of CEM

Both metritis and CEM will show similar symptoms of lethargy, fever, and soft, enlarged uterus. CEM produces a significant volume of mucopurulent (mixture of pus and mucous) approximately ten to fourteen days after mating with an infected stallion. 

The following symptoms occur in mares affected by CEM:

  • Ultrasound findings show oedematous endometriums with increased blood flow to the cervical area and vaginal lining. 
  • Shortened estrus cycles.
  • Abortions and infertility 
  • Vaginal discharge.

Stallions and chronically infected mares show no clinical symptoms. Foals become infected with CEM shortly after birth from an infected mare and remain carriers at sexual maturity. 

What to do When You Suspect CEM Transmission

CEM is a controlled disease because it’s a potential economic threat to the horse industry. CEM is difficult and expensive to treat. The key to preventing the disease is identifying carrier animals, removing them from breeding programs, or treating them until they test negative. 

Suppose an owner suspects CEM due to mares exhibiting sub-optimal breeding performance or CEM clinical symptoms. In that case, the best action is to contact a veterinarian to sample the suspected horse as soon as possible. Isolate the horse and remove them from any breeding activities until a CF test and three cultures suffice to establish an actual negative CEM test status. 

How is Contagious Equine Metritis Treated?

CEM uterine infections in mares clear after three to four weeks. The bacteria continue to thrive within the clitoral fossa or sinuses, making the mare a chronic carrier of CEM. 

After a mare is diagnosed with CEM, thoroughly cleaning the mare’s clit recesses must occur to treat the bacterial infection. Vets will recommend chlorhexidine surgical scrub as the topical washing agent. The application of nitrofurazone ointment after the scrub is a crucial step in ridding the horse of the bacterial burden, so owners must do this step with extreme diligence. 

In mares unresponsive to conservative treatment, the possibility of clitoral sinus surgical excision becomes a reality. This last resort procedure clears the area potentially harboring the bacteria. 

Stallions infected with CEM must receive daily sheathe and fully extended penis washes for five consecutive days. The wash must utilize a chlorhexidine surgical scrub to wash the penis and sheath thoroughly. The application of nitrofurazone ointment must follow the washing process. The stallion undergoes retesting ten days after the last day of treatment.

The Outcomes

The prognosis is good if a vet diagnoses a horse with CEM early. The main concern is the resultant infertility mares exhibit, leading to economic losses. The risk of chronic carrier mares and stallions infecting other horses with CEM is a significant issue in the equine husbandry industry. 

After a single treatment, most horses recover well, but some horses require repeat treatments. Any horses originating from endemic CEM countries require strict quarantine and treatment o upon arrival.

Is a CEM Vaccine Available?

CEM is a bacterial disease, and no commercial vaccine is available to provide horses with preventative care. 

How Can the Disease be Prevented?

The key to preventing CEM in horses is identifying and excluding infected horses before they become introduced into a breeding program. Horse breeders should only breed with CEM-negative animals.

All animals originating from countries where CEM is endemic must undergo preventative screening measures, including bacterial culture tests in both the breeding animals and a CF test in mares. 

Biosecurity when breeding horses is of the utmost importance. The cleanliness of equipment and staff during any artificial or natural breeding attempts must be a priority to avoid cross-contamination or transmission.

Accurate breeding records facilitate fast tracing of affected horses if a vet or client reports a CEM case from a specific breeding program. Good records must include breeding dates, stallions used, mares mated, and staff involved.

Stallions must undergo annual Taylorella equigenitalis cultures shortly before starting any breeding season. 

Arabian brown horse

The End

Contagious Equine Metritis is an economically significant venereal disease that exposes horses to infection during artificial insemination or natural breeding practices.

The subclinical nature of the disease in stallions poses the most significant risk to the horse industry as most breeders remain unaware of the infection until it is too late. Unsuccessful breeding attempts, prolonged infertility in mares, and extended breeding cycles result in a costly lesson learned if stallions are not tested regularly before breeding. Read our article and find out How Long is a Horse Pregnant?

The United States classifies CEM as a foreign disease on its shores because it is currently a CEM-free country. It is a federal law that any mare or stallions over the age of two years imported from any other country must undergo quarantine and testing for CEM to ensure the horse industry remains protected.