Pyometra

Signs appear during dioestrus, after oestrus has ended. Common findings are vaginal discharge (76.7% in one series of bitches), anorexia, depression, increased thirst and urination, vomiting and sometimes diarrhoea. Fever, dehydration, abdominal pain and pale or congested mucous membranes may be found. Closed-cervix cases lack discharge, may show abdominal distension and are more severely ill. Blood work often shows leucocytosis with a left shift, monocytosis, anaemia and raised urea and creatinine. Ultrasound shows an enlarged uterus with thickened walls and fluid in the lumen.

Pyometra is a suppurative bacterial infection of the uterus in which pus accumulates in the uterine lumen. It arises in the progesterone-dominated luteal phase: progesterone, possibly aggravated by oestrogen, causes cystic endometrial hyperplasia by stimulating endometrial gland proliferation and secretion, and it also suppresses uterine immunity, closes the cervix and reduces myometrial contractions. Opportunistic bacteria from the vagina, most often Escherichia coli, then infect the altered endometrium, and E. coli is associated with more severe endometrial lesions. Endotoxin from Gram-negative bacteria is a potent inducer of inflammation, so many animals become septic. When the cervix is closed, pus and bacterial products are retained and the illness is more severe.

Pyometra affects intact bitches and queens. In dogs it is one of the most common diseases of intact females, reported to affect about 25% before 10 years of age (Jitpean et al. 2014) or about 20% (Jitpean et al. 2017), with incidence differing between breeds. Middle-aged and older bitches after one or more non-pregnant oestrous cycles are typical, and disease is initiated during dioestrus. In a series of 111 dogs, 65% had open-cervix and 35% closed-cervix pyometra, and sepsis was present in 77% of closed-cervix versus 51% of open-cervix cases. Escherichia coli was isolated in pure culture in 57.7% of cases in a Brazilian dog and cat series.

Uterus (endometrium, myometrium), cervix, ovaries and corpus luteum, vagina, kidneys, peritoneum (after rupture), bloodstream (sepsis)

Ovariohysterectomy (spaying) removes the risk of recurrence. Bitches kept for breeding after medical treatment should be bred at the next oestrus.

Good after ovariohysterectomy; reported mortality 3-4% (Jitpean 2014) or 3-10% (Jitpean 2017), 1% postoperative in one series of 315. Peritonitis from uterine rupture occurs. Recurrence is likely at later cycles after medical treatment.