Many years ago, I was visiting a friend’s cat in the vet hospital. In the cage next door was a very, very sick female cat. She was so ill with pyometra, a dire uterine infection, that the vet couldn’t even spay her until he got her stabilized. Here’s what you need to know on this deadly disease.

1. It all starts with hormones

When a cat goes into heat, the levels of a hormone called progesterone increase dramatically. This allows the uterine lining to thicken in preparation for pregnancy and the cervix to open in order for sperm to enter the uterus. After a heat cycle ends, progesterone levels remain high for several weeks. If a cat goes into heat several times and does not get pregnant, the thickened uterine lining develops cysts.

2. Then come the bacteria

Because the cat’s cervix is open while progesterone levels are high, bacteria normally found in the vagina can make their way into the uterus. Add to that the fact that high progesterone levels also keep disease-fighting white blood cells out of the uterus — because they would kill sperm cells and prevent fertilization — and you’ve got a perfect breeding ground for nasty infections.

3. Symptoms

The symptoms of pyometra depend on whether the cervix is open or closed when the infection develops. If the cervix is open, you may see pus or bloody discharge coming from your cat’s vagina or stains in her bedding. (As a side note, it’s never normal for a cat to have bloody vaginal discharge, even when she’s in heat.) If the cervix is closed, the infection is trapped in the uterus and you won’t see any discharge. As the infection gets more severe, you’ll see signs like lethargy, depression, loss of appetite and excessive drinking and urination.

4. How pyometra is diagnosed

Any very sick intact female cat who is drinking a lot and has a swollen or painful abdomen is generally assumed to have pyometra. A vet will run a blood test, collect discharge from the vagina to see if bacteria are present, and take X-rays to see if the swollen uterus is visible. If the X-rays are inconclusive, the vet may also want to perform an ultrasound exam.

5. Pyometra is a life-threatening emergency

If you think your cat has pyometra, don’t wait until the next day to get an appointment with your regular vet. Go directly to the emergency clinic. Without immediate treatment, toxins will build up in the bloodstream and cause acute renal failure as the infection overwhelms the body’s defenses. Another possible complication is that the uterus can rupture, causing the infection to spill into the abdominal cavity and cause fatal peritonitis.

6. Surgery is the most common treatment

An emergency spay is the treatment of choice for pyometra. But depending on how sick the cat is when she presents to the clinic, the vet may need to use IV fluids and antibiotics and other methods to stabilize her enough to survive the surgery. Although medical treatment is possible with hormones called prostaglandins, which open the cervix and cause the uterus to contract, vets will recommend against it except in very rare cases, because the long-term success rate for this treatment is pretty low.

7. Although it’s rare, even spayed cats have been known to develop pyometra

The best way to prevent pyometra is to have your cat spayed before the age of six months. But if the spay was done incorrectly and some uterine or ovarian tissue is left in the cat’s body, it’s possible for the remaining uterine stump to get infected.

Have you lived with or rescued an intact cat who developed pyometra or a spayed cat who got stump pyometra? Did you have the cat spayed or did you try medical treatment? What was the outcome? Share your stories in the comments.

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About JaneA Kelley: Punk-rock cat mom, science nerd, animal shelter volunteer and all-around geek with a passion for bad puns, intelligent conversation, and role-play adventure games. She gratefully and gracefully accepts her status as chief cat slave for her family of feline bloggers, who have been writing their award-winning cat advice blog, Paws and Effect, since 2003.