

Pyometra is a deadly infection that affects unspayed female dogs and cats. This happens when the uterus gets infected and fills up with pus. Pyometra often comes as a result of the hormonal shifts present during the dog or cat's heat cycle.
The disease is more common in middle-aged to older female dogs and cats. However, it can occur in younger animals as well, especially those that have gone through multiple heat cycles without mating.
What Are the Types of Pyometra?
The condition is often categorized into two types: open and closed pyometra. Either type is considered a medical emergency that requires urgent veterinary care.
Open Pyometra
In this form, the cervix remains open, allowing pus and other discharge to exit the body through the vaginal canal. This can make the condition easier to detect, as owners may notice foul-smelling discharge, often accompanied by lethargy and a loss of appetite.
Open pyometra is generally less immediately life-threatening because the infection can drain, reducing the risk of uterine rupture.
Closed Pyometra
In closed pyometra, the cervix is sealed, trapping pus and infection inside the uterus. This form is more dangerous because the infection cannot easily escape, leading to rapid toxin buildup in the bloodstream.
Here, the swollen uterus can also rupture. This can result in internal bleeding and widespread infection, which are life-threatening emergencies. Closed pyometra is often harder to diagnose early because there is no visible discharge, and symptoms may appear more suddenly.
How Does Pyometra Develop?
Pyometra usually develops after a heat cycle when the hormone progesterone increases to prepare the uterus for a possible pregnancy. Here, the cervix will be opened up, allowing bacteria to sneak in.
Next, the cervix will close. During this time, the uterine lining thickens and produces secretions, while the immune system becomes suppressed. If there is no pregnancy, the secretions present within the uterus may serve as an ideal space for bacteria to grow.
The infection itself causes the uterus to fill with pus, causing swelling and pain. If the cervix is open, then the pus may drain out. If it’s closed, then it stays trapped.
The most common bacteria involved in pyometra are Escherichia coli. Other notable species can come from Staphylococcus, Streptococcus, and Pseudomonas.
What Are the Risk Factors for Pyometra?

While infection is the main cause, there are certain factors that can increase the risk of this disease. Here are the common risk factors for pyometra:
Age and Reproductive History
The risk of pyometra increases with age. The most commonly affected dogs and cats are those who are middle-aged. Additionally, pets that have undergone multiple heat cycles without mating are also more susceptible.
Each heat cycle exposes the uterus to hormonal changes that can lead to the thickening of the uterine lining. If they are unspayed, they are susceptible to bacterial growth within the uterus.
Breed Predisposition
Some breeds are genetically predisposed to developing pyometra. These are dogs such as:
Rottweilers
Bernese Mountain Dogs
Cavalier King Charles Spaniels
For cats, these are breeds like:
Hormonal Treatments
Treatments that are used to suppress heat cycles and prevent pregnancy are called hormonal treatments. These treatments can increase the chances of pyometra. This is due to the synthetic progesterone or estrogen in these drugs, which can cause hormonal imbalances.
With an imbalance of hormones, the uterus will be exposed to these hormones for an extended period. This results in the dog and cat’s immune system weakening, making them vulnerable to bacterial infection.
Weakened Immune System
Dogs and cats with compromised immune systems are also at risk of pyometra. When their immune response gets weaker, the body will have a harder time fighting off infections. This makes it easier for bacteria to come in and grow.
Frequently Asked Questions
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