Pyometra in Croatian cats ‒ a rare cause of death, with the first report of concurrent pyometra and pneumonia in a cat

Pyometra is a severe infection of the uterus with accumulation of pus within the uterine lumen, and is a relevant clinical problem that can be lethal. Mortality of cats from pyometra has rarely been investigated in the world, and there is no such research from Croatia. The aim of the study was to perform retrospective pathological research on pyometra-deceased cats from Croatia. Further, the study describes concurrent pyometra and pneumonia causing death in a single cat, which has, to the authors’ knowledge, not been reported before. The study included cats that died from pyometra from 2009 to 2022. The necropsy reports and histological slides of these cats were reviewed. From the investigated population of 2152 deceased cats, including 908 female cats, four cats died due to pyometra, corresponding to mortality of 0.19% (of the entire investigated population), and 0.44% (of the population of female cats). All the cats were non-pedigree, with an average age of 10.2 years. Apart from pyometra, a one-year-old cat was affected by pyothorax and multifocal to coalescing abscesses in the uterine wall and left lung, with intra-lesional Gram-positive cocci. The current study reports low mortality from pyometra, mostly affecting older cats, which corresponds to the literature data. The study also reports the first case of pyometra and pneumonia caused by Gram-positive bacteria as the coinciding causes of the death in a single cat, which differs from the literature data stating that the most frequent cause of feline pyometra is the Gram-negative Escherichia coli. This study presents valuable information for future disease prevention, health preservation, and the welfare of cats, while also demonstrating that uncommon bacteria may cause pyometra, and may affect organs other than the uterus.