JPC SYSTEMIC PATHOLOGY

REPRODUCTIVE SYSTEM

DECEMBER 2024

R-B05

 

Signalment (JPC #1844806): A mare

 

HISTORY: This mare's uterus was inoculated with a bacterial suspension 14 days previously. She developed a mucopurulent vaginal discharge.

 

MICROSCOPIC DESCRIPTION: Uterus: Diffusely, the superficial endometrial stroma is mildly expanded by moderate numbers of lymphocytes, fewer macrophages, plasma cells, and neutrophils. Multifocally, low numbers of neutrophils transmigrate the endometrial epithelium. There is mild congestion and edema diffusely within the endometrium.

 

MORPHOLOGIC DIAGNOSIS: Uterus: Endometritis, lymphoplasmacytic, diffuse, mild, breed unspecified, equine.

 

ETIOLOGIC DIAGNOSIS: Endometrial taylorellosis 

 

ETIOLOGY: Taylorella equigenitalis

 

DISEASE: Contagious equine metritis (CEM)

 

GENERAL:

• CEM, caused by Taylorella equigenitalis, a microaerophilic gram-negative coccobacillus, is a highly contagious venereal disease of mares that is characterized by endometritis, transient infertility, and rarely abortion
• Stallions do not develop clinical disease, but can transmit the organism; recovered mares can harbor the organism for several months and are an important reservoir
• May cause substantial economic damage in a valuable equine breeding population

 

PATHOGENESIS:

sinus) and stallions (urethral fossa, urethral sinus, preputium); carrier mares and stallions are the most important source of infection

• Transmission occurs by the venereal route, through natural service or artificial insemination, or by contaminated equipment

• The endometritis causes transient infertility

 

TYPICAL CLINICAL FINDINGS: 

• Mucopurulent vaginal and cervical discharge within 48 hours of exposure and lasting 2-3 weeks
• Transient infertility (clinical hallmark of the disease) or rare early abortion
• No evidence of systemic illness

 

TYPICAL GROSS FINDINGS:

• Endometrial folds are edematous and swollen
• Hyperemia and edema of the cervix and palpably firm uterine walls
• Cloudy, odorless, viscid, mucopurulent exudate on endometrial folds, cervix, and vagina
• Salpingitis is an uncommon finding

 

TYPICAL MICROSCOPIC FINDINGS:

• The best indication of endometritis in all species consists of accumulations of plasma cells and foci of lymphocytes in the stroma
• Mild to moderate diffuse, acute endometritis and cervicitis that is initially predominantly neutrophilic but can persist as a mild, multifocal, lymphoplasmacytic endometritis for several months
• Subepithelial neutrophils, lymphocytes, plasma cells, macrophages (numbers and proportions vary with stage of disease), and edema
• Transmigrating neutrophils within the epithelium; degenerating neutrophils 

within uterine glands

 

ADDITIONAL DIAGNOSTIC TESTS:

• Serial bacteriologic cultures because of fastidious nature of the organism
• PCR

 

DIFFERENTIAL DIAGNOSIS:

Common causes of equine uterine infection

• Infectious endometritis – similar clinical, gross, and histologic changes; bacteriologic culture to differentiate
  • Beta-hemolytic streptococci (S. equi ssp. zooepidemicus: beta-Strep.)
  • Klebsiella pneumoniae
  • Escherichia coli
• Persisent mating-induced endometritis
  • Anatomic or physiologic abnormalities that cause uterine fluid accumulation or impair normal uterine clearance 
• Chronic degenerative endometritis
  • Increased fibrosis, cystic glands, lymphangiectasia
• Endometrial biopsy in subfertile mares used to evaluate the stage of cycle, inflammation, presence of fibrosis, dilation of lymphatics, and loss of glands

 

REFERENCES:

1. Foster RA, Premanandan C. Female Reproductive System and Mammae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:1279-1280, 1283.
2. Schlafer DH, Foster RA. Female genital system. In: Maxie MG, ed. Jubb, Kennedy, Palmer’s Pathology of Domestic Animals. Vol 3. St. Louis, MO: Elsevier; 2016:388-389, 393.
3. Schnobrich MR. Disorders of the reproductive tract. In: Reed SM, Bayly WM, Sellon DC, eds. Equine Internal Medicine. 4^th ed. St. Louis, MO: Elsevier; 2018:1246-1252.

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