What are Metritis?
Taylorella equigenitalis in the Alcaligenaceae family is the bacteria responsible for contagious equine metritis. There are two known strains of the bacteria, one of which is resistant to streptomycin, an antibiotic used to fight bacterial infections. While the infection can normally be treated with disinfectants and antibiotics, it can cause a mare to spontaneously abort, or be unable to conceive due to various reproductive problems. Once the infection has run its course, or symptoms have been eliminated, mares can become carriers of the bacteria for years afterward. Therefore, screening tests are extremely useful in preventing the spread of this disease.
Contagious equine metritis is a highly contagious venereal disease that affects horses. Spread primarily through mating, the transferred bacteria responsible can cause a serious infection that can temporarily compromise fertility in mares. Stallions are asymptomatic, and can spread the disease to many mares before the disease is noticed. Carrier and symptomatic mares can also spread the disease, both through mating and to their foals.
Symptoms of Metritis in Horses
While infected stallions do not show any signs of the infection, mares can have temporary reproductive symptoms that typically clear up in days to weeks. Most symptoms appear within 10 to 14 days after mating has occurred that transferred the disease. Signs of the infection include:
- Temporary infertility lasting a few weeks
- Mucopurulent, vaginal discharge, grayish yellow in color
- A premature return to estrus following a shortened cycle
- Intermittent vaginal discharge, sometimes during pregnancy
- Various bacterial infections
- Endometritis
- Cervicitis
- Vaginitis
- Infertility
- Spontaneous abortion
- Uterine inflammation
- Uterine lesions that decrease over time
- Infection of the fallopian tubes
Causes of Metritis in Horses
The Taylorella equigenitalis bacteria is transferred primarily during mating, but there are other ways it can spread. The main ways the infection can transfer are:
- Infected stallions who show no symptoms, but can carry the bacteria for months to years, spreading it to virtually every mare they mate with
- Infected mares with or without symptoms, who can spread it to stallions or foals
- Foals can be born infected, or become infected through their mothers, and carry the bacteria, spreading it once they reach maturity
- Infected semen used for artificial insemination
- Infected instruments or equipment that comes into contact with horse genitalia
- Contaminated hands or other objects
Diagnosis of Metritis in Horses
A diagnosis of contagious equine metritis can be made based on the results of bacterial cultures, serological testing, and test mating, and depends on the isolation of the T. equigenitalis bacteria.
Bacterial cultures are the most accurate tests, but can still result in false negatives due to the fragile nature of the bacteria. A quick and reliable transportation method needs to be used to ensure correct results. Samples collected from mares include vaginal discharges, swabs of genital tissues, cultures taken from cervix or endometrium, samples taken during estrus, and samples of the placenta if pregnant. Cultures can be taken from aborted fetuses and from the genitalia of foals. Samples from stallions include ejaculatory fluid, and swabs from genitals and the urethra. Multiple samples should be taken at intervals of seven days or more. While samples are being taken, no antibiotics should be used.
There are a variety of serological tests available, but they are unable to detect if a horse is a carrier. Many tests can distinguish between strains of the bacteria to identify the presence of T. equigenitalis specifically, and include a PCR assay, molecular genotyping, and immunological methods, such as indirect immunofluorescence, staining, and ELISA testing. Since antibodies are not always found in infected animals, serology can be unreliable, but can be helpful as screening tests.
Test mating entails breeding a suspected stallion to a healthy mare, then testing the mare through bacterial cultures and serology for infection.
Treatment of Metritis in Horses
Horses infected with contagious equine metritis are often quarantined, and are treated with disinfectants and antibiotics for several weeks. Once treated, horses are then re-tested and released upon testing negative for the bacteria. Treatments may need to be repeated.
Disinfectants such as chlorhexidine, sodium hypochlorite, and ionic and nonionic detergents are used to wash external genitalia on both stallions and mares. The extended penis of stallions is also disinfected, then treated with a local antimicrobial, such as nitrofurazone ointment, for 5 days. Mares can often clear the infection without treatment, but that can take several months. Antibiotics are sometimes given. Mares can also be treated with disinfecting and applying a local antimicrobial to clitoral tissues, although persistent cases may require surgical excision of the clitoral sinuses to completely clear the infection.
Recovery of Metritis in Horses
The treatment of stallions is usually successful. Mares often respond well to treatments, although a proportion of mares can remain carriers for years without showing any symptoms. There is often an incomplete immunity after the infection has cleared, with reinfection possible in a short period of time.
You will most likely be given disinfectants to wash your horse daily, and possibly medications to administer. A re-evaluation of your horse’s condition can be performed after 10 days of treatment to ensure the elimination of the infection. Repeated treatments may be necessary in persistent cases.
Prevent this highly contagious disease through controlled breeding, using screening tests for stallions and mares. Identification of carrier and infected horses is necessary to eliminate those horses from breeding programs. Practicing good hygiene, sanitation during breeding, and the frequent decontamination of possible infected objects and hands can help to prevent the transfer of T. equigenitalis. There is currently no vaccine available.
