Pyometra: Desexing cats and dogs can prevent uterus infection

The prevalence of pyometra seems to be creeping up again. Picture: Shutterstock
The prevalence of pyometra seems to be creeping up again. Picture: Shutterstock

Pyometra is a condition I see occasionally in dogs and cats, although anecdotally the prevalence seems to be creeping up again.

The word pyometra is based on the Greek words "pyo" for pus and "metra" for uterus, and basically that's exactly what it is: a pus-filled uterus.

It usually occurs in undesexed (or as veterinary team members say, "entire") animals, and can be life threatening if not addressed.

The risk of pyometra is one reason that we recommend desexing of non-breeding animals.

Interestingly, the condition is more common in countries where companion animals are not routinely desexed, like Sweden.

Pyometra most commonly affects middle-aged to older dogs and cats, but I have seen occasional cases in animals just over the age of one year old and it has been reported in dogs as young as four months old.

The average age of affected dogs is 7 years, while the average age of affected cats is about 5.5 years.

Previous treatment of animals with hormones increases the risk of pyometra.

Signs vary depending on whether the cervix is open or closed. If the cervix is open, there is usually continuous or intermittent vaginal discharge which is pussy or bloody. It can be hard to tell, as fastidious animals will often lick themselves clean. But owners often notice spots on their pet's bedding or on the floor.

But if the cervix is closed, there is no discharge. Instead, the pus builds up, filling up the uterus like a balloon. Closed pyometra is often associated with more severe signs, including a reduced or absent appetite, lethargy, increased thirst, increased frequency and volume of urination, vomiting, diarrhoea, abdominal pain, abdominal bloating and weakness.


Often these animals experience a fever. A closed pyometra can rupture, spilling pussy contents into the abdomen and leading to septic peritonitis, a severe and life-threatening condition.

Diagnosis is based on the history (this condition often develops a few months after an animal has been on heat or in season), physical examination, blood tests to determine the severity of the condition and to guide supportive care, and abdominal imagining, which may include x-rays, ultrasound or both. It is easier to diagnose an open pyometra, but diagnosis can be tricky in the absence of vaginal discharge and unusual clinical signs.

There are other conditions that can cause the uterus to swell, including hydrometra (water in the uterus) and mucometra (mucus in the uterus), although affected animals aren't usually as sick as those with pyometra.

The treatment of choice is surgical removal of the uterus and ovaries. Because the uterus is compromised by disease, it is more fragile and - unlike a normal uterus - is full of pus, the surgery tends to be a bit more involved than a routine desexing procedure. It can be a bit like removing a water balloon while trying not to burst it.

To give you an idea of size, I have removed a pyometra weighing 4kg from a dog weighing (before surgery) about 20kg. Many of my colleagues have removed even larger pyos (every veterinarian and veterinary nurse I know has a story about the biggest pyo they have ever removed).

In addition, unlike healthy pets underdoing a routine desexing procedure, dogs and cats with pyometra may be systemically unwell. Affected animals are also usually treated with intravenous fluids, antibiotics and of course pain relief. They usually require longer periods in hospital. All of this increases the cost associated with the treatment.

Medical treatment is sometimes used in young, otherwise healthy breeding animals with an open pyometra. This tends to be more costly than surgery alone, and animals undergoing treatment need to be monitored very closely. If treatment does not succeed the patient may require surgery.

Pyometra can be prevented by ensuring that your pet is desexed.

If you suspect that your pet has signs of pyometra, seek veterinary attention immediately. The earlier treatment is instituted, the better the prognosis.

  • Dr Anne Quain BVSc (Hons), MANZCVS (Animal Welfare), Dip ECAWBM (AWSEL) is a lecturer at the Sydney School of Veterinary Science and a practising veterinarian.