Contagious
equine metritis
(CEM)
is an extremely contagious venereal disease that is acquired
primarily via breeding. While this disease can be carried by either
mares or stallions, it is the mare
that
suffers the ill effects of the infection. Stallions do not show any
symptoms of CEM, but mares often will have a thick discharge from the
vagina, and will be unable to conceive during the point at which the
infection is active.
Etiology
The causative agent of CEM is a microaerophilic gram-negative coccobacillus Taylorella equigenitalis in the family Alcaligenaceae.
Symptoms
Stallions are asymptomatic (no symptoms), but may carry the bacterium on their external genitalia for years, and therefore be persistent carriers and transmitters of the disease.
In fact, to be technical, the stallion does not become "infected" with the CEMO, but rather harbours it in the manner of a commensal organism.
One of the first symptoms in a mare is likely to be that she is not pregnant after one or more breeding cycles.
It should be noted that although failure to establish pregnancy is a common sequela of infection, abortion is rare.
There are three categories of infection in the mare:
The acutely infected mare: This mare will present with an actively inflamed uterus, with an obvious milky-mucoid (pus) discharge from the external genitalia when she returns to estrus (and the cervix relaxes) - and quite often that return to estrus is earlier than anticipated
The chronically infected mare: This mare shows a lesser level of uterine inflammation, and an associated lower level of vulval discharge. It is likely that mares in this category will be more difficult to treat in order to clear the organism.
The carrier mare: This mare shows no symptoms of the disease, but is harbouring the CEMO in the reproductive tract. This mare is more difficult yet to clear, and as a result of no obvious external signs represents a greater risk to the non-identified at-risk population
The incubation period in the mare from the time of exposure to the onset of active symptoms (or diagnostic ability) is 2-12 days.
Transmission
The following includes practices that may result in, or increase, the likelihood of transmission in the face of T. equigenitalis presence:
Etiology
The causative agent of CEM is a microaerophilic gram-negative coccobacillus Taylorella equigenitalis in the family Alcaligenaceae.
Symptoms
Stallions are asymptomatic (no symptoms), but may carry the bacterium on their external genitalia for years, and therefore be persistent carriers and transmitters of the disease.
In fact, to be technical, the stallion does not become "infected" with the CEMO, but rather harbours it in the manner of a commensal organism.
One of the first symptoms in a mare is likely to be that she is not pregnant after one or more breeding cycles.
It should be noted that although failure to establish pregnancy is a common sequela of infection, abortion is rare.
There are three categories of infection in the mare:
The acutely infected mare: This mare will present with an actively inflamed uterus, with an obvious milky-mucoid (pus) discharge from the external genitalia when she returns to estrus (and the cervix relaxes) - and quite often that return to estrus is earlier than anticipated
The chronically infected mare: This mare shows a lesser level of uterine inflammation, and an associated lower level of vulval discharge. It is likely that mares in this category will be more difficult to treat in order to clear the organism.
The carrier mare: This mare shows no symptoms of the disease, but is harbouring the CEMO in the reproductive tract. This mare is more difficult yet to clear, and as a result of no obvious external signs represents a greater risk to the non-identified at-risk population
The incubation period in the mare from the time of exposure to the onset of active symptoms (or diagnostic ability) is 2-12 days.
Transmission
The following includes practices that may result in, or increase, the likelihood of transmission in the face of T. equigenitalis presence:
- Not
using a disposable AV liner;
- Sharing
AV's between stallions;
- Not
cleaning AV's adequately between use;
- Not
using a disposable protective barrier on the rear of the breeding
mount (where the penis contacts) during collection and changing it
between stallions;
- Not
washing the breeding mount with a suitable agent (e.g.
Chlorhexidine) between stallions;
- Not
using an antibiotic extender (or an antibiotic to which the organism
is not sensitive) - it should be noted that even with the use of a
suitable antibiotic, transmission may still occur;
- Sharing
of penis washing equipment without sterilization in between
stallions or good aseptic technique (this includes hands - e.g. use
of disposable latex gloves when washing and/or guiding the penis
that are then discarded, or thorough scrubbing of the hands in
between collections/breedings with a suitable bactericide);
- Other
poor sterility or aseptic technique associated with the
collection/breeding process.
Treatment
Treatment for both sexes is primarily topical with the intent of removing the offending organism and any smegma in which it may be located.
Scrubbing the clitoral sinuses and fossa in the mare with a 4% solution of chlorhexidine for 5 consecutive days, following each daily treatment with packing of the area with a 0.2% nitrofurazone ointment (such as Furacin) is one protocol.
An alternative treatment is 5 days of scrubbing with Betadine, followed by packing with Silvidine cream.
Systemic antibiotic treatment may be provided in conjunction with the topical cleansing. It should be noted that until the acutely infected mare has resolved internal tract presence of T. equigenitalis, there is little point in implementing external treatment.
Repeated treatment of the mare is often required to eradicate the bacterium, so the mare is tested again 28 days after the last treatment, and if still positive a repeat of the treatment and testing is performed until found to be clear.
In rare cases of persistent infection in the mare, surgical removal of the clitoral sinuses may be necessary. This was once a common part of treatment of the infected mare, but is now only used in extreme cases.
Treatment for the stallion is similar, consisting of thorough cleansing of the external genitalia, with the penis fully extended and erect. Additionally the urethral fossa and sinus are cleansed.
A 2% Chlorhexidine solution is adequate for the stallion. It is recommended by some that following the Chlorhexidine wash, the penis be rinsed with sterile saline to avoid irritation, this is not however included in other protocol recommendations.
Following this washing, the region is coated with 0.2% nitrofurazone cream or a similar ointment. Again, these treatments are continued for five consecutive days.
Systemic antibiotics may also be used, oral Trimethoprim-Sulfa being suitable. Once treated and tested clear, a stallion that previously tested positive for presence of T. equigenitalis will be required to test-breed two mares that were confirmed clear of the pathogen prior to that breeding.
The mares are subsequently tested following breeding as discussed above under "diagnosis" to confirm absence of a carrier state in the stallion.
If a mare tests positive for T. equigenitalis during the post-breeding testing, treatment and further testing of the stallion is recommenced, as well as treatment of the test mare. Most stallions however typically respond favourably to a single course of treatment, and are found to be clear upon the post-treatment test breeding.
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