What is Pyometra, or ‘Pyo’?

A “pyo” is the common phrase used to describe a pyometra — a very serious and potentially fatal infection of the uterus (womb). It is one of the most common reproductive disorders in the bitch, but unfortunately, the initial symptoms are often vague and subtle, meaning that by the time we see these patients they are often critically ill. 

What causes it?

After every season the entire (unneutered) bitch will enter a false pregnancy (technically, the dioestrous phase of her cycle). In this period, which lasts a little over 2 months, the ovary releases progesterone to make sure that the uterus is prepared to maintain pregnancy, even if there aren’t actually any puppies in there. One effect of this is that the lining of the uterus becomes thickened and secretes fluid – this is the cystic endometrial hyperplasia complex.

Normally, this fluid will be reabsorbed at the end of the false pregnancy; however, sometimes it becomes infected as bacteria penetrate the uterus. The uterine secretions are a perfect growth medium for bacteria that otherwise would be essentially harmless (they’re generally normal vaginal and skin commensals).

The multiplication of the bacteria causes the uterus to fill with pus, causing severe systemic illness, septic shock and if untreated, death from septicaemia or shock.

Surely that can’t be common though?

Actually, studies suggest that pyometra affects 2.2% of the entire female population every year. Put another way, by 10 years of age, 24% of entire bitches will suffer a pyometra – that’s one in four. The high-risk period is the 2-4 months after a bitch’s season.

Are all pyos the same?

No, there are two different forms of the disease:

  • Open Pyo – this is usually a less severe form. It occurs when the cervix (the muscular valve that separates the uterus from the vagina) remains open. This allows the pus in the uterus to drain – meaning that the infection tends to grumble on, but is less likely to be rapidly fatal.
  • Closed Pyo – this is the most dangerous type, where the cervix is closed, preventing the pus from draining. These dogs become progressively more and more sick until the pressure in the uterus causes it to burst internally, leading to peritonitis, collapse, and death.

What are the symptoms?

Usually, symptoms start off fairly mild and become progressively worse. Some only apply to an open pyo, and some are common to both types. The usual signs are:

  • Off colour
  • Loss of appetite
  • Increased thirst
  • Increased urination
  • Licking at her back end (in open pyos)
  • Discharge from the vulva (usually red or brown, but occasionally white or yellow, pus – open pyos only)
  • Vomiting
  • Swollen abdomen
  • Collapse and death

Can it be treated?

Yes, if caught early enough. The treatment of choice is ovariohysterectomy – emergency surgery to remove the swollen uterus and the pus it contains before it can burst. If the bitch is in a state of dehydration and collapse, however, she may not be well enough to survive surgery immediately, so she will be admitted for intensive care (on a drip, antibiotics, and anti-inflammatories) until she is fit for surgery.

Obviously, the surgical route means that the bitch cannot be used for breeding again in the future, but it is the only treatment available for a closed pyo. There is a medical option; using antibiotics to fight the infection and certain hormones to shut down the uterus and push out the infection. However, this option may also impair future fertility,  doesn’t always work, and about 60% of the time the pyo will recur after the next season.

If I suspect my dog has any of these symptoms, what should I so?

A pyo is potentially fatal, so if you are at all suspicious, bring her in for our vets to check as soon as possible! We’ll carry out a full examination, and if necessary we’ll carry out an ultrasound scan to see if the uterus is indeed full of pus.