Simply put it is an infection of the uterus caused by bacteria, often E.coli, entering via the cervix that leads to the accumulation of pus. It can be either 'open' or 'closed' and this refers to the cervix. Open pyos are generally easier to spot and diagnose as pus/discharge leaks from the vagina. In a closed pyo there is no discharge and if other symptoms are not recognised the dog can very quickly develop blood poisoning and/or the womb can become so distended with pus that it ruptures. It is therefore an extremely serious and life-threatening condition, particularly the closed variety as there is no outlet for the accumulation of pus.
Pyo obviously affects unspayed bitches - there is a condition called stump pyometra where uterine tissue left in the body after spaying becomes infected but this is relatively rare. Pyo is linked to hormonal changes during seasons and will usually occur about 8 weeks after a season; it can affect dogs at any age but older entire bitches are much more likely to be affected due to repeated changes in the uterus over many heat cycles. The preferred treatment is removal of the uterus and ovaries (spaying); some cases of open pyo can be treated with drugs but success is not guaranteed and once a bitch has had a pyo there is an extremely high likelihood of recurrence. Some affected bitches show more signs than others but for a closed pyo with no discharge symptoms may be lethargy, depression, inappetence, vomiting and increased thirst/excessive drinking.
