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Basics ⬇

Outline

BASICS

Definition!!navigator!!

  • Genital infection of stallions and mares caused by Taylorella equigenitalis
  • A reportable, highly contagious, nonlife-threatening disease
  • Transmitted primarily by coitus but also by contaminated equipment
  • Stallions are asymptomatic carriers
  • Clinical signs only in mares; range from none to acute endometritis
  • Abortion may occur in mid- to late gestation
  • Regulations for interstate shipment (USA) of semen and embryos lack uniformity

Pathophysiology!!navigator!!

Stallions

  • The organism is harbored in various external regions of the genital tract including fossa glandis, urethral sinus, smegma, terminal urethra, preputial surface, and pre-ejaculatory fluid
  • Indirect transmission can occur by not following appropriate sanitary protocols when handling stallion external genitalia

Mares

  • Up to 30–40% of mares bred by an infected stallion develop the disease:
    • A mare may also be exposed by breeding with fresh-cooled or extended semen from a carrier stallion
    • Indirect transmission can occur by inadequate sanitary protocols when handling stallions and mares, fomite spread, and contaminated equipment, including speculums, tail wraps, and obstetric equipment
  • Clinical signs range from none to acute endometritis. Acute infection may remain asymptomatic, allowing the organism to persist for prolonged periods within a population of horses
  • The organism initially is found in the endometrium and cervix and less frequently in the vagina, vulva, clitoris, and oviducts
  • From 3 weeks to 4 months following exposure, the organism occasionally can be recovered from the ovarian surface, oviduct, uterus, cervix, and vagina
  • The organism is more reliably isolated from the clitoral fossa and sinuses as it can persist in these sites
  • Mares may be mechanical carriers via smegma of the clitoral fossa
  • The organism may be harbored throughout pregnancy. It is subsequently also recoverable from placentae of positive mares and genitalia of colts and fillies
  • Acquired in utero, at parturition, or via contact with bedding or pasture contaminated with infected fluids

Systems Affected!!navigator!!

Reproductive

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

Transmission is dependent on carrier stallion live cover or shipped semen, or the use of contaminated equipment.

Signalment!!navigator!!

Breeding-age mares and stallions from countries identified as CEM affected.

Signs!!navigator!!

Stallions

  • Inapparent infection, retained locally on external genitalia, no systemic antibody response is detectable
  • 1 report (necropsy) of infection involving testes and accessory sex glands

Mares

  • Within 2–7 days (experimental) or up to 13 days (field challenge) of infection, mares develop varying amount of odorless, grayish, mucopurulent discharge
  • Intrauterine fluid accumulation often present with transrectal ultrasonography
  • Diffuse endometritis and cervicitis—severe and plasmacytic by 14 days; declines and persists as mild, diffuse, and multifocal for as long as 2 weeks
  • Shortened diestrus because of premature luteolysis
  • Temporary infertility
    • Short-term infertility differential diagnosis should consider CEM even in the absence of inflammation or vaginal discharge
    • Pregnancy may successfully be maintained in the presence of infection
    • Abortion may occur in mid- to late gestation
  • No systemic involvement
  • Reexposure experimentally associated with no to minimal signs of disease

Causes!!navigator!!

  • 2 strains of T. equigenitalis based on sensitivity to streptomycin (majority of strains are sensitive)
  • Taylorella asinigenitalis resembles T. equigenitalis
    • Has been isolated from donkey jacks at routine testing for CEM
    • There is cross-reactivity with the CF utilized to identify mares recently infected with T. equigenitalis

Risk Factors!!navigator!!

  • Carrier stallion
  • Contaminated equipment
  • No lifelong immunity
  • Previous exposure does not afford absolute protection against subsequent challenge

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Bacterial and fungal endometritis
  • Pyometra
  • Vaginitis
  • Urinary tract infection
  • Urine pooling
  • Neoplasia of the uterus or vagina
  • Persistent hymen

CBC/Biochemistry/Urinalysis!!navigator!!

Unremarkable

Other Laboratory Tests!!navigator!!

  • Speculum examination
  • Collection of cervical discharge
  • Isolation of organism

Imaging!!navigator!!

Ultrasonography—intrauterine fluid suggestive of endometritis.

Other Diagnostic Procedures!!navigator!!

Serology

  • Detectable antibody in acute cases
    • Mares only CF positive 21–45 days post infection
  • No value in stallions, because contamination is surface only

Bacterial Cultures

  • Stallions—urethral fossa and urethral sinus, distal urethra, penile skin, and preputial folds
  • Mares—clitoral sinus and fossa; endometrium, vaginal fluid, and cervix of estrus mare
  • Exacting culture requirements for T. equigenitalis
    • Immediately place swabs in Amies charcoal medium
    • Keep at 4°C for transport. Do not freeze.
  • Plate samples within 48 h of collection in chocolate agar at 5% CO2
  • Colonies usually form in 2–3 days; a recent streptomycin-sensitive strain may take as long as 6 days
  • Reportable disease that requires a federally approved laboratory for identification

Cytology (Mares)

  • Presence of polymorphonuclear cells indicative of endometritis
  • Presence of morphologically suggestive bacteria
    • Free or phagocytized Gram-negative coccobacilli seen individually or in pairs, arranged end to end

Test Breeding (Stallions)

  • Breed to 2 known CEM-negative mares following 3 negative stallion cultures over 1 week
  • Post breeding, mares assessed by repeated PCR and culture; seroconversion (CF antibodies) between 21 and 45 days
  • Does not consistently lead to colonization and seroconversion of test mares; therefore test breed in conjunction with direct assessment of stallion

PCR

  • Rapid and cost-effective test for mares and stallions
  • Not sufficiently validated for screening of cooled or frozen semen, and embryos
  • Experimentally can discriminate between T. equigenitalis and T. asinigenitalis
  • Used in conjunction with culture, more effective technique than culture alone

Pathologic Findings!!navigator!!

N/A

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

Under federal supervision at approved quarantine station.

Stallions

  • Completely extrude and wash penis in chlorhexidine 4% scrub
  • Remove all smegma, especially from the urethral fossa and skin folds of prepuce
  • Dry all structures completely
  • Nitrofurazone 0.2% or silver sulfadiazine 1% dressing is applied liberally
  • Repeat above procedure daily for 5 days

Mares

  • Acute endometritis:
    • Intrauterine antibiotics—crystalline penicillin (5–10 × 106 IU for 5–7 days), ampicillin (2 g in 60 mL normal saline for 3–5 days)
    • Systemic antimicrobials—trimethoprim–sulfamethoxazole (30 mg/kg PO for 5 days)
  • Clitoral carriers:
    • Cleansing of the clitoral fossa and sinuses with chlorhexidine scrub to remove all smegma
    • Pack with nitrofurazone 0.2% or 1% silver sulfadiazine ointment
    • Repeat daily for 5 days
  • May be beneficial to combine above protocols to prevent colonization of clitoris during treatment
  • Several treatment cycles may be necessary to eliminate infection/carrier state

Retest all treated mares and stallions no less than 21 days following above protocols to ensure freedom from colonization with T. equigenitalis.

Surgical Considerations!!navigator!!

Mares—clitoral sinusectomy or clitorectomy for intractable cases.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

See Treatment.

Contraindications!!navigator!!

N/A

Precautions!!navigator!!

  • Mucosal irritation from drugs
  • Concurrent systemic antimicrobial treatment of mares and stallions may reduce bacterial load and therefore diminish chance of successful culture in carrier animals

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Culture (Timing)

  • Swabs—at least 7 days after the last day of treatment with systemic antimicrobials, or 21 days following topical antimicrobials, must elapse before testing
  • Use most current protocol as dictated by the country regulations. In USA (USDA/APHIS):
    • Mares—3 consecutive estrus periods
    • Stallions—every 2 days for 3 sets

Culture (Locations)

  • Mares—swab the clitoris and endometrium at estrus before breeding; swab during abnormal estrous intervals
  • Stallions—swabs from teaser and breeding stallions before season begins, as described in Bacterial Cultures

Culture (Equipment)

Disposable gloves, sleeves, and speculum. Clean disposable tail wrap.

Prevention/Avoidance!!navigator!!

  • All horses older than 2 years entering the USA from CEM-affected countries must follow treatment and testing protocol
  • Mares—culture 3 times in 7 days, then treat for 5 days; if 3 negative cultures are obtained, the mare is released
  • Stallions require a set of negative cultures followed by negative test breeding to 2 known CEM-negative mares; if positive, treat, then repeat cycle until 3 consecutive, negative culture results and negative test breeding results are obtained
  • Use artificial insemination when feasible or permitted by breed society regulations

Expected Course and Prognosis!!navigator!!

Recovery with treatment.

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Synonyms!!navigator!!

Formerly Haemophilus equigenitalis.

See Also!!navigator!!

N/A

Abbreviations!!navigator!!

  • CEM = contagious equine metritis
  • CF = complement fixation test
  • PCR = polymerase chain reaction
  • USDA/APHIS = United States Department of Agriculture/Animal and Plant Health Inspection Service

Suggested Reading ⬆ ⬇

Baverud V, Nystrom C, Johansson KE. Isolation and identification of Taylorella asinigenitalis from the genital tract of a stallion, first case of a natural infection. Vet Microbiol 2006;116:294–300.

Carleton CL, Donahue JM, Marteniuk JV, et al. Bacterial and fungal microflora on the external genitalia of male donkeys (Equus asinus). Anim Reprod Sci 2015;153:62–68.

Dennis S, Pearson LK, Campbell AJ, Tibary A. Interstate equine semen and embryo shipment regulations in the United States and their implications on control of disease transmission. J Equine Vet Sci 2014;34(7):897–902.

Klein C, Donahue JM, Sells SF, et al. Effect of antimicrobial-containing semen extender on risk of dissemination of contagious equine metritis. J Am Vet Med Assoc 2012;241(7):916–921.

Schulman ML, May CE, Keys B, Guthrie AJ. Contagious equine metritis: artificial reproduction changes the epidemiologic paradigm. Vet Microbiol 2013;167(1):2–8.

Timoney PJ, Kristula MA, Ford ES, et al. Contagious equine metritis: efficacy of US post-entry testing protocols for identifying carrier stallions and mares. J Equine Vet Sci 2016;39:S60.

Wakeley PR, Errington J, Hannon S, et al. Development of a real time PCR for the detection of Taylorella equigenitalis directly from genital swabs and discrimination from Taylorella asinigenitalis. Vet Microbiol 2006;118:247–254.

Watson ED. Swabbing protocols in screening for contagious equine metritis. Vet Rec 1997;140:268–271.

Wood JL, Kelly L, Cardwell JM, Park AW. Quantitative assessment of the risks of reducing the routine swabbing requirements for the detection of Taylorella equigenitalis. Vet Rec 2005;157:41–46.

Author(s) ⬆

Author: Peter R. Morresey

Consulting Editor: Carla L. Carleton