Emily Rätsep

Animal Health Laboratory, University of Guelph, Kemptville, ON

AHL Newsletter 2022;26(1):19.

A 13-year-old Hanoverian mare aborted December 1, 2021.  The mare was up to date on vaccines with no recent history of illness, and no changes on farm beyond coming in at night starting November 15.  The aborted fetus and placenta were submitted for postmortem examination at the AHL in Kemptville.

Postmortem findings for the fetus included icterus and marked subcutaneous edema, with small to moderate volumes of translucent amber-coloured fluid in the thorax and abdomen.  Petechial hemorrhages were observed throughout the musculature of the body wall and across the epicardial surface, and the liver was markedly enlarged with small tan foci and fibrin scattered across the capsular surface (Fig. 1). The placenta was relatively unremarkable grossly, though mild edema was appreciated and the chorioallantoic surface appeared thickened and darker red in the pregnant vs the non-pregnant horn.

Histologically, there were clusters of mixed macrophages, lymphocytes and plasma cells in the epicardial connective tissue, extending slightly into the underlying myocardial interstitium.  Scattered similar inflammatory cells, along with neutrophils, were present in sinusoids throughout the liver, along with frequent bile canalicular plugs and similarly pigmented hepatocytes.  A definitive correlate for the tan foci observed grossly was not histologically apparent.  A mixed population of inflammatory cells was also observed both within and surrounding capillaries in various organs including the stomach, cerebellum, intestines, and within lymph nodes and perinodal connective tissue.

The most notable histological changes were in the placenta where there was patchy marked edema of the chorioallantoic stroma and a mixed population of inflammatory cells scattered predominantly in perivascular positions throughout the chorioallantois.  Scattered poorly preserved neutrophils were also observed admixed with cellular debris in the most severely-affected areas.  Warthin-Starry silver stain demonstrated numerous argyrophilic spirochetes within the periphery of the edematous areas of the placental stroma (Fig. 2A).  The same organisms were strongly immunoreactive for antibodies to Leptospira spp. (Fig. 2B).  Kidney submitted for PCR was also positive for Leptospira spp.

The leptospiral placentitis resulting in both fetal hypoxia and systemic bacterial spread to the fetus was determined to be the underlying cause of the abortion.  While icterus and interstitial nephritis are the most consistently reported pathological changes in aborted fetuses due to Leptospira spp., placental lesions similar to those described above have also been observed, and spirochetes have been consistently found in placental tissue (1).  Mares that abort due to a leptospiral infection may present with no clinical signs.  However, the bacteria can be shed for several weeks following abortion, and therefore could be of zoonotic concern on farm (2).   AHL

Figure 1. Aborted equine foal with icterus, subcutaneous edema, fibrinous abdominal effusion and thoracic effusion.

Figure 2.  Leptospiral placentitis in a Hanoverian foal.  Chorioallantois with immunohistochemistry for Leptospira (A) and Warthin-Starry silver stain (B).  There is both positive red immunostaining (arrowheads) and silver staining (arrows) of innumerable individual leptospires in the edematous chorioallantois.

References

1. Hodgin EC, et al.  Leptospira abortion in horses. J Vet Diagn Invest 1989;1:283-287.

2. Donahue JM and Williams NM. Emergent causes of placentitis and abortion. Vet Clin N Am:Equine Practice 2000;16(3):443-456.