Unilateral pyelonephritis associated with chronic endometritis in a mare

Introduction

Equine endometritis is a major cause of infertility and 60% of mares have been diagnosed with bacterial endometritis (LeBlanc and Causey, 2009) [8] . Generally, if a mare fails to resolve physiological endometritis, it can lead to severe inflammation especially when combined with pathogenic organisms (Christoffersen and Troedsson 2017) [5] . Sometimes, these organisms invade the endometrial glands resulting in infectious endometritis (Petersen et al., 2018) [9] . Bacterial infections in the renal pelvis and parenchyma can lead to pyelonephritis which may be of descending (haematogenous) or ascending origin (Reed et al., 2018; Sprayberry and Robinson, 2015) [10,15] . The present case describes the occurrence of the unilateral pyelonephritis associated with chronic endometritis in a mare.

Case history and observations

A 14 years old, Thoroughbred mare with a history of chronic endometritis was presented for post-mortem examination at Department of Veterinary Pathology, Veterinary College and Research Institute, Salem with the clinical history of chronic vaginal discharge for two months and pneumovagina. It was detected by the presence of foamy exudates in the vagina during the rectal examination. The animal was treated with antibiotics and a Caslick's operation/ vulvoplasty was perfoarmed at the Veterinary Clinical Complex, Veterinary College and Research Institute, Salem, to prevent penumovagina. Although, the animal initially responded positively to treatment, it eventually succumbed to chronic infection, likely exacerbated by old age and collapsed. Cytological smears were prepared from cervical and vaginal discharge and stained by the Giemsa-Leishman staining method. Sterile swabs from the purulent material in the renal pelvis were collected for bacterial culture. Kidney and endometrium samples were fixed in 10% formalin, processed and stained with Hematoxylin-Eosin (H&E) following the method described by Bancroft and Gamble (2008) [2] .

Results and Discussion

Pneumovagina/wind sucking is a common underlying problem in mare that predisposes them to ascending contamination (Samper et al., 2007) [13] . In this condition, the vaginal lumen becomes distended with air and foamy exudates, which interferes with the uterus's protective mechanisms, allowing bacteria, debris and foreign objects to enter the genital tract (Brinsko, 2011a; Brinsko, 2011b) [3,4] . Ascending bacterial infection and debris accumulation can result in chronic endometritis. Cytological smears from a cervical swab showed marked lymphocytic infiltration, consistent with the observations of Rudolph et al. (2017) [12] in case of endometritis. In this case, failure of medical treatment was largely attributed to old age, which reduces uterine clearance; older mare is less resistant infection and require longer periods to eliminate irritants from the uterus compared to younger, healthy mares (Samper et al., 2007) [13] . Grossly, petechial haemorrhages were observed in the pericardium and endocardium (Figure 1), along with mild bronchopneumonic changes, a moderately enlarged pale liver with a focal infarct, a splenic infarct, purulent discharge in the renal pelvis (Figure 2) and a thick, hemorrhagic endometrial wall filled with blood-tinged exudate (Figure 3). Histopathological examination revealed multifocal congestion and infiltration of inflammatory cells, predominantly lymphocytes with very few neutrophils, in the endometrial mucosa (Figure 4 & 5) as well as mild periglomerular fibrosis, tubular degeneration and lymphocytic infiltration in the renal interstitium (Figure 6).

In this study, the cardiac lesions confirmed the presence of septicaemic and toxaemic conditions. The mare, clinically diagnosed with chronic endometritis and pneumovagina, succumbed to septicaemia due to chronic bacterial infections and old age. Culture of the renal swabs revealed growth of Enterobacter sp. and Staphylococcus sp., findings similar to those reported by Jennifer (2007) [7] and Parveen et al. (2020) [14] . Septic nephritis, resulting in abscess/ pus and purulent discharge leads to pyelonephritis which can further cause sepsis, renal failure and death in both humans and companion animals (Ross, 2011; Gorsane et al., 2018) [11,6] . Therefore, the present case was diagnosed as pyelonephritis associated with chronic endometritis in mare. In this case, renal lesions may have occurred due to bacterial toxins delivered via the hematogenous route, as well as ascending infections associated with chronic endometritis. The kidney, being a highly vascularized organ, is particularly susceptible to bacterial invasion during septicaemia, placing horses at high risk for septic nephritis (Auer and Stick, 2019) [1] . The observed microscopic lesions in the kidney correlate with these pathophysiological mechanisms.

Conclusion

Based on the results, the mare died due to septicaemic shock by pyelonephritis and chronic endometritis.

Acknowledgement

AcknowledgementThe authors are highly thankful to the Dean, Veterinary College and Research Institute, Salem for providing facilities to carry out this work.

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