Pyometra is the accumulation of pus in the uterus of a bitch (female dog) due to infection. It forms part of a very complex disease known as CEHMEP (Cystic endometrial hyperplasia, mucometra, endometritis, pyometra complex) which is life-threatening and can lead to systemic shock, renal failure and death.
Pyometra: how it occurs
Pyometra happens because of the hormonal influence of oestrogen and progesterone on the uterus. Female dogs have endometrial glands in the uterus that are stimulated by reproductive hormones. These endometrial glands become cystic with each subsequent heat, creating the perfect environment for bacterial infection.
The infection occurs directly after the bitch is on heat. The reproductive hormones suppress the local immunity of the uterus, and also the systemic immunity of the bitch. This makes the bitch more susceptible for uterine infection and subsequent systemic infections. Because of the reduced immunity of the reproductive tract and the bitch in general, the normal bacteria that inhabits the vagina, will migrate into the reproductive tract and/or urinary tract. This leads to subsequent infections of the bladder (cystitis), kidneys (nephritis) and the uterus (endometritis/pyometra), which can lead to serious complications such as systemic infection or septic shock.
Another downside of these reproductive hormones during the dioestrus phase (the period after ovulation when the dominant hormone is progesterone) is that it causes partial closure of the cervix, trapping the infection in the uterus. Pus accumulates in the uterus, serving as a reservoir that infects the rest of the body.
Why contraception doesn’t help
The condition is more likely to occur with every subsequent heat the bitch has (which is on average every 6 to 7 months). With every subsequent heat the endometrial glands become more and more cystic, increasing the chances of the bitch developing pyometra with each consecutive heat. Although the disease is mainly seen in middle-aged to older bitches, the condition already starts at a young age and only manifests as a clinical condition when the bitch is older. Contraceptives in bitches are contraindicated because of this condition. Because contraceptives are hormones, they only exacerbate the condition in bitches. Contraceptives will in fact stimulate bitches to develop pyometra.
The bitch that does develop pyometra has to undergo extensive medical and surgical treatment, with a high risk of developing kidney failure, systemic infection, septic shock or death. Due to the complex nature of this disease and the high risk associated with it, the only way to prevent this disease is to sterilise the bitch at a young age. An intact bitch is highly likely to develop this condition later in life, not to mention the other risks and diseases associated with intact bitches.