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EQUINE VETERINARY EDUCATION
Equine vet. Educ. (2020) 32 (8) 444-448 doi: 10.1111/eve.13010
Review Article A review of fungal endometritis in the mare
C. J. Scott Rossdales Veterinary Surgeons, Beaufort Cottage Stables, Newmarket, Suffolk, UK Corresponding author email:
camilla.scott@
rossdales.com
Keywords: horse; mare; infertility; fungal; endometritis
Summary Fungal endometritis is a relatively rare cause of infertility in the mare, accounting for only 1–5% of all cases of endometritis. However, it remains a challenge to the clinician due to difficulties in diagnosing and effectively treating affected mares, resulting in a high rate of recurrence and a guarded prognosis for ongoing fertility. Often occurring as an opportunistic infection, the most common causes of fungal endometritis in the mare are yeasts (Candida spp.) and moulds with septated hyphae (Aspergillus spp.). Early detection and identification of the causative agent are vital when choosing appropriate treatment as sensitivities to commonly used antifungals vary significantly. Assessing in vitro sensitivity for each isolate is accordingly recommended. Treatment of mares with fungal endometritis is multifaceted and includes; correction of any anatomical defects, uterine lavage and systemic and/or intrauterine infusion of antifungals. Concurrent bacterial infection is common so anticipation and subsequent treatment of bacterial endometritis is also often required.
Introduction
Endometritis is a leading cause of infertility in the mare and a major cause of economic loss to the equine breeding industry (Riddle et al. 2007). Whilst fungal infections only account for 1–5% of all cases of endometritis (Dascanio et al. 2001), due to difficulties in accurately identifying the causative agent and a lack of controlled studies and pharmacokinetic data on antifungals, effective treatment can be a challenge. In addition, with a high incidence of recurrence and a guarded prognosis for future fertility, fungal endometritis becomes an important consideration in the problem mare. Fungal organisms consist of both yeasts, that are single-
celled organisms, and moulds/hyphae, which are long, branching, filamentous structures. Certain fungal organisms such as Candida spp. are dimorphic and have the ability to exist in both forms under specificconditions. Themost common causes of fungal endometritis following the culture of 102 fungal isolates, were yeast (69%, primarily Candida spp.), mould with septated hyphae (26%, primarily Aspergillus spp. [18%]) and mould with nonseptated hyphae (5%, primarilyMucor spp. [4%]) (Beltaire et al. 2012). Distinction between the different forms of fungal organisms is vital when considering treatment and assessing in vitro sensitivity for each isolate is recommended, as sensitivities to commonly used antifungals vary significantly.
Aetiology
Fungal endometritis in the mare is typically thought to occur as an opportunistic infection, with the primary reservoir being the caudal reproductive tract, including the vagina and
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clitoral fossa. Risk factors for infection include; poor perineal conformation, compromised uterine defenses, necrotic foci (such as retained fetal membranes, abortion and trauma following dystocia) and endocrine/immune disorders resulting in immunosuppression. Fungal endometritis is often identified following the repeated use of intrauterine antimicrobials. Whilst the exact mechanisms are still unknown, the combination of a disrupted vaginal flora caused by the antimicrobial treatment and potential iatrogenic introduction of pathogens into the uterus has been suggested (Hinrichs et al. 1992). Progesterone supplementation may also increase the risk of mycotic infection due to decreased neutrophil function, reduced uterine contractility and increased cervical tone (Evans et al. 1986; Watson 1988). In 152 mares presented to Utrecht University, the
incidence of fungal endometritis was highest in barren (74%), followed by maiden (16%) and foaling (9%) mares. Risk factors in this study included previous intrauterine antibiotic treatment (87%), pneumovagina/urovagina (39%), excessive intrauterine fluid (33%) and a history of dystocia/retained fetal membranes (18%) (Stout 2008). Concerns have been raised about the risk of venereal transmission as samples taken from the reproductive tract of
healthy stallions have been shown to be positive for filamentous fungi and/or yeasts; however, there are no current studies to confirm semen as a source of infection in mares (Malmgren et al. 1998; Rota et al. 2011).
Diagnosis
Horses presenting with fungal endometritis are often older, multiparous mares with a history of chronic infertility. Clinical signs may include a purulent vaginal discharge and excessive amounts of flocculent fluid within the uterine lumen on palpation and ultrasound examination (Fig 1), whereas other cases may be subclinical. Adefinitive diagnosis is made based on endometrial
cytology, culture or quantitative polymerase chain reaction (qPCR). Endometrial cytology should be performed using a double-guarded uterine swab, cytobrush or following centrifugation of the effluent from a low volume uterine lavage (Fig 2). An endometrial brush will yield higher number of cells, whilst a low volume lavage is likely to produce a more representative sample of the entire uterus when compared with a standard swab technique (Cocchia et al. 2012). Positive smears provide a quick and reliable diagnosis and will often show evidence of inflammation in addition to fungal elements. Various stains can be used to identify fungal organisms including; trichrome, periodic acid-schiff (PAS), Gram stain, Romanovsky and modified Wright’s (Diff-Quick).1 Yeast will be visualised on cytology as single-celled organisms, spherical/oval in shape and approximately 3–4 lm
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