Pyometra is a serious and life threatening infection that results in a pus-filled uterus. This infection occurs when an animal isn’t spayed and goes into heat creating the perfect environment for bacterial growth, resulting in the accumulation of pus inside the animal’s uterus. An intact female can develop pyometra at any age, but it is more common in older pets. Symptoms range from obvious pus draining from the vagina to more subtle symptoms such as lethargy and decreased appetite. If pus is retained in the uterus, the animal’s abdomen will be distended and the animal will become very sick, very quickly. If caught early, a physical exam may be enough for a diagnosis. However, more often, bloodwork and abdominal x-rays will be required. The most common and effective treatment is surgery to remove the infected uterus and ovaries (a spay). Hormone therapy is another treatment option, but not all pets are candidates, and the success rate is much lower, putting your animal at higher risk.


A normal cat uterus.

     Pyometra removed at Harbor Point Animal Hospital.


For more detailed information about this life threatening infection, see below!


What it is:

Pyometra is an infection in the uterus that is considered serious and life threatening. If not treated quickly and aggressively, pyometra can lead to death (Ward).

How it Happens:

Pyometra is a secondary infection that occurs as a result of hormonal changes in the female’s reproductive tract. During estrus (“heat”), white blood cells, which normally protect against infection, are inhibited from entering the uterus. This allows sperm to safely enter the female’s reproductive tract without being damaged or destroyed by these immune system cells. Following estrus, progesterone hormone levels remain elevated up to two months and cause thickening of the lining of the uterus in preparation for pregnancy and fetal development. If pregnancy does not occur for several consecutive estrus cycles, the uterine lining continues to increase in thickness until cysts often form within the tissues (a condition called Cystic Endometrial Hyperplasia). The thickened, cystic lining secretes fluids that create an ideal environment for bacteria to grow in. Additionally, high progesterone levels inhibit the ability of the muscles in the wall of the uterus to contract and expel accumulated fluids or bacteria (Ward). The combination of these factors often leads to infection.

When Does it Occur:

Pyometra may occur in any sexually intact young to middle-aged dog or cat; however, it is most common in older animals.

After many years of estrus cycles without pregnancy, the uterine wall undergoes the changes that promote this disease. Pyometra usually occurs two to eight weeks after the last estrus (ACVS).

Signs and Symptoms:

The clinical signs depend on whether the cervix remains open or not. If it is open, pus will drain from the uterus through the vagina to the outside. Pus or an abnormal discharge is often seen on the skin or hair under the tail or on bedding and furniture where the dog or cat has recently laid. Fever, lethargy, anorexia, and depression may or may not be present (Ward).

If the cervix is closed, pus that forms is not able to drain to the outside. It collects in the uterus ultimately causing the abdomen to distend. The bacteria release toxins that are absorbed into the bloodstream. Animals with closed pyometra become severely ill very rapidly. They are anorectic, very listless and very depressed. Vomiting or diarrhea may also be present (Ward).

Toxins released by the bacteria affect the kidney’s ability to retain fluid. Increased urine production occurs, and many animals drink an excess of water to compensate. Increased water consumption may occur in both open- and closed-cervix pyometra (Ward).


If the animal is examined early slight vaginal discharge and no other signs of illness is expected. However, most animals with pyometra are brought in after the illness has progressed. A very ill female dog or cat with a history of recent “heat” that is drinking an increased amount of water should be suspected of having pyometra. This is especially true if there is a vaginal discharge or a painful, enlarged abdomen (ACVS).

The animal’s white blood cell count will be elevated. Often, an elevation of globulins (a type of protein often associated with the immune system) in the blood will also be seen. The animal’s urine may also be more concentrated due to the effects of the bacteria on the kidneys (ACVS). However, these changes are not enough to diagnose pyometra as they may be present in any dog or cat with a major bacterial infection.

If the cervix is closed, radiographs (x-rays) of the abdomen will often identify the enlarged uterus. If the cervix is open, there will often be such minimal uterine enlargement that the radiograph will be inconclusive. An ultrasound examination may be helpful in identifying an enlarged uterus and differentiating that from a normal pregnancy. Ultrasound changes that indicate pyometra include increased uterine size, thickened uterine walls, and fluid accumulation within the uterus (Ward).


The preferred treatment is to surgically remove the infected uterus and ovaries, known as a spay. Dogs and cats diagnosed in the early stage of the disease are very good surgical candidates, although surgery is somewhat more complicated. Unfortunately, most pets are diagnosed with pyometra when they are quite ill. This results in a more complicated surgical procedure and a longer length of recovery. Antibiotics are usually given following surgery (Ward).

Is Surgery Necessary?

There is an alternative treatment for pyometra, however, it does not have a high success rate. Prostaglandins are a group of hormones that lower the blood level of progesterone, relax and open the cervix, and cause the uterus to contract and expel bacteria and pus. They can be used to treat this disease, but they are not always successful and have many limitations (Ward).

Is Treatment Necessary?

The chance of successful resolution without surgery or prostaglandin treatment is extremely low. If treatment is not performed quickly, the toxic effects from the infection can be fatal. If the cervix is closed, it is possible for the uterus to rupture, spilling the infection into the abdominal cavity (ACVS). This will also be fatal. Pyometra is a serious medical condition that requires prompt treatment.


ACVS, American College of Veterinary Surgeons. “Pyometra.” American College of Veterinary Surgeons. 2017. Web. 6 Mar. 2017.

Ward, Earnest. “Pyometra in dogs.” VCA. VCA_Corporate, 11 Dec. 2008. Web. 6 Mar. 2017.