Pyometra / dvm360 Fetch conference / Charolette North Carolina / March 15 2024 Dr. Shadi Ireifej

Pyometra is defined as a pus-filled uterus and ovaries due to endometritis (inflammation of the endometrium), metritis, (inflammation of the myometrium) and cystic endometrial hyperplasia and inflammation that occur in response to estrogen-induced endogenous luteal ovarian progesterone or exogenous progesterone, and a secondary Gram-negative bacterial infection (purulent endometritis), that ultimately results in systemic changes.
Cystic endometrial hyperplasia-pyometra complex is the most common uterine disorder of intact bitches. The incidence of pyometra is 19 to 25% in intact female dogs by the time they reach 10 years of age. It is seen in 19% of all intact female bitches. Without treatment the disease is fatal.
Pyometra occurs in middle to older age bitches, at an average of 8 to 9.36 years of age, with 3 to 66% (average of 20%) occurring in intact female dogs before 10 years of age (varying based on breeds). Affected animals can be any age with dogs ranging from 6 months to 18 years of age. Most are over 4 to 6 years of age and within 8 weeks of their last estrus. Nulliparous bitches are more often afflicted than multiparous and primiparous bitches.
Despite the common nature of this condition, the suspected causes of pyometra are multiple. Such causes include hormonal influences, the presence of an open cervix, structural uterine changes, dietary, and genetic influences. The most common and influential of these is hormonal influences.
Estrus promotes uterine cell growth, endometrial vascularization, uterine sensitivity, and uterine response to progesterone. These hormonal changes are less prominent in the face of estrogen. Hormonal imbalances or an abnormal response to the normal concentration of estrogen and progesterone alters uterine epithelial cells, facilitating bacterial adherence, colonization, and growth. Formation of the cystic hyperplasia-pyometra complex usually occurs in the early or first half of the diestrus phase. However, pregnancy and the luteal phase itself may be involved.
Postpartum bacterial presence or bacterial infiltration after breeding may occur due to the presence of an open cervix. Bacterial routes of access to the ovarian bursa or uterus include hematogenous, peritoneal, lymphatic, and ascending. The normal perineal and normal bitch vaginal flora include Escherichia coli (E. Coli). However, it has also been stated that the normal commensal bacteria of the vagina do not reflect the uterine organisms found. Mycoplasma and Ureaplasma organisms may be normal in canine genitourinary tract as well.
Retained fetal and placental tissues, obstetrical manipulations, and infectious abortions can also contribute to pyometra development.
A lower growth rate of E. coli from the B2 phylogroup was observed in dogs fed a raw meat-based diet than in those fed commercial dry feed. This may suggest that intestinal colonization by certain types of E. coli could be a risk factor for the occurrence of E. coli pyometra in bitches and that diet can influence intestinal colonization by such strains.
A genome-wide association study in the Golden Retriever breed found an increased risk of developing pyometra with a risk ratio of 3.3. The study identified four missense single nucleotide polymorphisms within the ABCC4 gene. One missense was located at chr22:45,893,198 (p.Met787Val) which showed complete linkage disequilibrium and the other locus identified was on chromosome 18 overlapping the TESMIN gene. Therefore genetic may play a role in predisposing some dogs to pyometra development.
The cause(s) described above, with progesterone being the main hormone involved, set the stage for formation of the cystic hyperplasia-pyometra complex, which usually occurs in the early or first half of the diestrus phase (a 15% incidence). However, pregnancy and the luteal phase itself may be involved. Less uterine androgen receptors are present in affected uteri as well. With bacterial involvement, infection develops and a secondary septicemia and endotoxemia can occur.