Serious severity

Pyometra

A life-threatening infection that fills the womb with pus, seen in unspayed female cats. It is a surgical emergency — without prompt treatment it is frequently fatal.

⚠️ Common symptoms

Lethargy and depressionLoss of appetiteIncreased thirst and urinationA swollen or distended bellyVomitingA foul, blood-tinged or pus-like discharge from the vulva (open pyometra)Fever, or in advanced cases a low body temperature and collapse

Pyometra is one of the most important reasons that veterinary surgeons urge owners to have female cats spayed. The word means, quite literally, "pus in the uterus," and that plain description undersells how dangerous the condition is: an infected, pus-filled womb can leak toxins into the bloodstream, send a cat into septic shock, and in the worst cases rupture into the abdomen. It is, without exaggeration, a killer of unspayed cats.

The disease is rooted in the normal hormonal cycle. After a queen comes into heat, progesterone prepares the uterus for a possible pregnancy by thickening its lining and quietening the local immune defences. If pregnancy does not follow, those same changes — repeated season after season — leave the uterus increasingly hospitable to bacteria. Eventually organisms ascend from the vagina, take hold, and the womb begins to fill with pus. This is why pyometra is overwhelmingly a problem of middle-aged and older intact females, and why the risk climbs with every unbred heat.

Vets divide the condition into two forms. In an open pyometra the cervix remains open, so owners often notice a foul, blood-tinged discharge — an unpleasant sign, but a useful early warning. In a closed pyometra the cervix is sealed, trapping the pus inside; there is no discharge to see, the uterus swells dangerously, and the only clues may be a generally sick cat who is off her food, drinking more, vomiting and developing a distended belly. Closed cases are the more lethal of the two precisely because they are easier to miss.

Treatment is surgical and urgent. The cat is first stabilised with intravenous fluids and antibiotics, then the infected uterus and ovaries are removed — essentially an emergency spay performed on an animal who is already ill. Caught early, most cats recover well and, having been spayed in the process, can never develop the condition again. Caught late, after rupture or sepsis, the prognosis falls sharply. The reassuring conclusion for owners is simple: routine spaying removes the risk almost completely, turning a potentially fatal emergency into something that need never happen at all.

🔍 Causes

Pyometra develops under the influence of the hormone progesterone in the weeks after a heat cycle. Progesterone thickens the uterine lining and dampens the local immune response, creating conditions in which bacteria — usually E. coli that have travelled up from the vagina — can multiply unchecked and fill the womb with pus. It is therefore a disease almost exclusively of unspayed (intact) female cats, becoming more likely with each heat the cat goes through without becoming pregnant, and more common in middle-aged and older queens. In an "open" pyometra the cervix is open and pus drains out; in a more dangerous "closed" pyometra the cervix is shut, so the pus accumulates with nowhere to go.

🛡 Prevention

Pyometra is almost entirely preventable by spaying. Removing the ovaries and uterus eliminates both the hormonal driver and the organ that becomes infected, which is one of the most compelling health reasons to neuter any female cat not intended for a carefully managed breeding programme. Owners of intact queens should be alert in the four to eight weeks following each heat — the highest-risk window — and avoid the use of progesterone-based hormone treatments, which sharply increase the risk.

💊 Treatment

The definitive treatment is emergency surgery to remove the infected uterus and ovaries (ovariohysterectomy — the same operation as routine spaying, but far higher-risk on a sick cat). The cat is stabilised first with intravenous fluids and antibiotics to combat shock and infection, then taken to surgery as soon as she is fit enough. Medical management with hormone drugs is occasionally attempted in valuable breeding queens with an open pyometra, but it is slower, less reliable and carries a high risk of recurrence, so surgery remains the strongly preferred option. The outlook is good when the condition is caught and operated on early, and poor once the uterus has ruptured or the cat has become septic.

When to see a vet: Treat pyometra as an emergency. Any unspayed female cat that becomes unwell in the weeks after a season — especially with lethargy, poor appetite, increased drinking, a swollen abdomen or a discharge from the vulva — needs to be seen by a vet without delay. A closed pyometra is particularly dangerous because there is no obvious discharge, so vague illness in an intact queen should never be dismissed. Diagnosis is usually quick, combining the history with blood tests and an ultrasound or X-ray of the abdomen.

A historical veterinary plate of the female reproductive organs — pyometra fills the uterus with pus

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⚕️ Medical disclaimer

This information is educational only and is not a substitute for veterinary advice.
Symptoms overlap between conditions — only a vet can diagnose accurately.
Never withhold treatment or self-medicate based on information found online.
When in doubt, call your vet. Early intervention almost always leads to better outcomes.

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