Persistent Uterine Infection: Where to Start?

Introduction
A uterine infection can be detrimental to fertility in a number of ways; firstly, if the infection is active, the neutrophils recruited to combat the microorganisms are likely to bind and phagocytose sperm introduced during insemination thereby reducing the likelihood of conception. Secondly, persistence of a uterine infection beyond Day 6–7 after ovulation can interfere with pregnancy either by direct infection of the embryo as it enters the uterine lumen, or because the associated inflammation triggers endometrial PGF2α release leading to premature luteolysis. In the longer term, persistent or recurrent uterine infections may lead to a disturbed uterine environment, and instigate chronic degenerative changes in the endometrium that compromise the ability to maintain pregnancy; however, the evidence that recurrent infections result in chronic endometrial damage is currently lacking.

Diagnosis
In some instances, there are clear indications from a mare’s history (failure to establish pregnancy despite mating with a fertile stallion at a number of cycles; irregular cycle length) or from an initial gynaecological examination (vulval discharge; cloudy uterine fluid; excess uterine oedema) that the uterus is inflamed and/or infected. For a long time, the diagnostic cornerstone in the case of a suspected uterine infection has been the use of a guarded endometrial swab to recover a sample of uterine cells/mucus for microbiological and/or cytological examination. However, there is increasing evidence that isolated culture or cytological examination of material collected using a simple swab is not always sufficient to definitively demonstrate the presence of pathogenic microorganisms. For example, E. coli appears to stimulate a very modest neutrophil response (Leblanc 2010), while a swab can easily be contaminated with organisms from the caudal vagina or perineum such that a positive culture alone is not definitive proof of an active endometritis; for these reasons, it is sensible to consider the results of cytology and microbiology in combination before drawing conclusions. Even then, small volume uterine lavage and uterine biopsy both appear to deliver material that is more sensitive and specific in the diagnosis of uterine infection. [...]