Pyometra is not contagious in the traditional sense. It has long been classified as a non-transmissible infectious disease, meaning one pet cannot “catch” pyometra from another the way they might catch kennel cough or parvovirus. The infection develops internally, driven by a combination of hormonal changes and bacteria that already live in the animal’s own body. That said, one recent case report has complicated the picture slightly, and the bacteria involved do carry some risks worth understanding.
Why Pyometra Is Not a Typical Infection
Pyometra is a bacterial infection of the uterus that occurs in unspayed female dogs and, less commonly, cats. But the bacteria don’t come from the outside world in the way a contagious disease spreads. In up to 90% of canine cases, the culprit is E. coli, a bacterium that normally lives in the dog’s own intestinal tract. The same specific strain found in an affected dog’s gut is typically the one found in her infected uterus.
The infection happens because of hormonal conditions, not exposure to a sick animal. After a heat cycle, during a phase called diestrus, progesterone levels rise and cause changes in the uterine lining: the glands secrete more fluid, the uterine walls stop contracting normally, the cervix closes, and the local immune response weakens. This creates a warm, stagnant environment where bacteria from the dog’s own digestive tract can travel upward and multiply unchecked. The disease is multifactorial, involving hormonal shifts, genetic predisposition, and pre-existing uterine changes. Nearly 25% of all unspayed female dogs develop pyometra before age 10 in populations where routine spaying is uncommon.
One Documented Case of Transmission
In 2022, researchers described what they believe is the first case of E. coli associated with pyometra being transmitted between two female dogs living together. Molecular testing confirmed that the exact same bacterial strain colonized the gut of one dog and later appeared in the uterus of her housemate, who then also developed pyometra during the same cycle. The researchers suggested the bacteria likely spread through contact with feces or vaginal discharge.
This is a single case report, and even the peer review noted it’s difficult to rule out coincidence, since dogs living together often share similar gut bacteria and may simply have developed pyometra independently. Still, the finding prompted the authors to recommend that in households with more than one unspayed female, a dog with suspected or confirmed pyometra should be kept separated from other intact females until the infection is resolved. The key distinction: even in this case, the pyometra itself wasn’t transmitted. The bacteria were. The second dog still needed the right hormonal conditions in her own body for the infection to take hold.
Risk to Humans
You cannot develop pyometra from your dog. However, the E. coli strains involved in pyometra are not harmless bystanders. Genomic research has found that many of these strains belong to the same high-risk genetic lineages that cause urinary tract infections and bloodstream infections in humans. Some carry genes for multidrug resistance. This doesn’t mean handling a dog with pyometra will make you sick, but basic hygiene matters. If your dog has open pyometra (the type where pus drains from the vulva), wash your hands after cleaning up discharge and keep the area where she rests clean.
Open vs. Closed Pyometra
Pyometra takes two forms, and the distinction matters both for recognizing the condition and for understanding any exposure risk to other pets. In open pyometra, the cervix remains partially open, allowing infected fluid to drain. You’ll typically notice a foul-smelling, often bloody or yellowish discharge from the vulva. This is the form where other animals in the household could theoretically come into contact with bacteria-laden fluid.
Closed pyometra is more dangerous for the affected dog because pus accumulates inside the uterus with no way out. There’s no visible discharge, which makes it harder to detect. Dogs with closed pyometra tend to become seriously ill more quickly, with vomiting, lethargy, loss of appetite, and a visibly distended abdomen. Because there’s no external discharge, the exposure risk to other animals is minimal, but the medical urgency is higher.
Which Animals Are at Risk
Any unspayed female dog or cat can develop pyometra, though dogs are affected far more often. The infection typically appears about a month after a heat cycle, and the risk increases with age as the uterine lining undergoes repeated hormonal stimulation over successive cycles. Certain cat breeds, including Sphynx, Siamese, Ragdoll, Maine Coon, and Bengal, have a higher risk than others. Cats often show very minimal signs, making the condition easy to miss. The use of hormonal medications for reproductive control, such as progestins or estrogen compounds, is a recognized risk factor in both species.
Treatment and Survival
Surgery to remove the uterus and ovaries is the standard treatment and is highly effective. In a large study of over 400 dogs treated surgically, 97% survived to hospital discharge. Dogs with a ruptured uterus, dehydration, or signs of kidney stress had longer hospital stays, but rupture occurred in only about 3% of cases. For animals intended for future breeding, medical management using hormone-based medications can sometimes resolve the infection, though recurrence rates are significant.
Spaying as Prevention
Spaying eliminates the risk of pyometra entirely by removing the uterus and the hormonal cycle that drives the disease. For cats and dogs not intended for breeding, this is the most reliable form of prevention. One caveat: if ovarian tissue is accidentally left behind during surgery (a situation called ovarian remnant syndrome), the remaining tissue can continue producing hormones, and a “stump pyometra” can develop in whatever uterine tissue remains. This is uncommon but is the reason veterinary guidelines emphasize complete removal of the ovaries and uterus, including the cervix in cats that have already had pyometra.