What is pyometra?
Pyometra is a secondary infection that occurs as a result of hormonal changes in the female’s reproductive tract. Following estrus (heat), the hormone progesterone remains elevated for up to two months and causes the lining of the uterus to thicken in preparation for pregnancy. If pregnancy does not occur for several consecutive estrus cycles, the uterine lining continues to increase in thickness until cysts form within the uterine tissues (a condition called cystic endometrial hyperplasia). The thickened, cystic lining secretes fluids that create an ideal environment for bacterial growth.
In addition, the muscles of the uterus cannot contract properly either due to thickening of the uterine wall or the high levels of the hormone progesterone. This means that bacteria that enters the uterus and fluids that have accumulated cannot be expelled.
During estrus, white blood cells, which would normally protect against infection by eliminating bacteria, are inhibited from entering the uterus. This normal occurrence allows sperm to safely enter the female’s reproductive tract without being damaged or destroyed by these immune system cells.
The combination of these three factors can often lead to life threatening infection.