Decidual Cell Reaction and Endometritis in a Guinea Pig

A female, research-naive, strain 13 guinea pig with no previous significant health history was noted to have a persistent vaginal discharge. On physical examination a soft mass was noted in the lower abdomen accompanied by a serosanguineous vaginal discharge. Due to a poor prognosis, the animal was euthanized. At necropsy, the left uterine horn was markedly enlarged and contained a large amorphous mass. Light microscopy examination showed that the mass had dense areas containing stromal cells surrounded by connective tissue, congested blood vessels, areas of necrosis, hemorrhage, and occasional cyst formation. In some areas numerous bacteria, both rods and cocci, were noted and the uterine wall showed increased thickness caused by a polymorphonuclear cell inflammatory infiltrate. Bacteriological culture and isolation from the vaginal discharge revealed a mixed infection with Escherichia coli, Bacteroides fragilis, Proteus mirabilis, Enterococcus spp., and α-hemolytic Streptococcus spp. while culture and isolation from the uterus revealed a mixed infection with E. coli, Pseudomonas aeruginosa, B. fragilis, and Globicatella sanguinis. The pathology findings were consistent with decidual cell reaction and endometritis. Vaginal bleeding is not a common clinical sign in decidual cell reaction and usually does not require treatment since the lesion in many cases resolves on its own by apoptosis and resorption. However, in this case, systemic antibiotics may have been beneficial to treat the endometrial infection. These findings suggest that decidual cell reactions may occur accompanied by, or as a result of, intrauterine infections in guinea pigs. The potential role of bacteria in decidual cell reaction should be further explored in guinea pigs.