Pyometra is a poly-systemic, dioestrual disorder that is hormonally mediated, distinguished by cystic endometrial hyperplasia (CEH) with infiltration of inflammatory cells due to secondary bacterial infection. Pyometra is reported primarily in older, sexually intact female dogs (>8 yr old), a few weeks after the last heat cycle (estrus).
Pyometra do not occur in spayed animals, since a spay surgery involves removing the uterus. It may be more common in dogs that have never had puppies.
Pyometra VS metritis: Metritis is defined as inflammation of the endometrium lining of the uterus that develops in the immediate postpartum period and occasionally after abortion, miscarriage, or breeding. But, pyometra is an infection of the uterus unrelated to pregnancy.
Acute pyometra: This occurs suddenly and produces evident signs.
Chronic pyometra: Persistent inflammation and produce no noticeable signs or mild symptoms.
The bacteria that is most often responsible for uterus infection is ubiquitous, commensal, gram-negative bacteria like Escherichia coli (sometimes staphylococci and Proteus sp).
Chronic and extreme pyometra inflammation is associated with a fatal response triggered by diverse forms of tissue injury termed systemic inflammatory response syndrome (SIRS) and this can be a life-threatening condition.