Ascending placentitis in a Standardbred mare
Keywords: ascending, placentitis, yeast, bacteria abortionNote: Although is scientifically more accurate to refer to the fetal components of the placenta as the fetal membranes rather than the placenta (the placenta consisting of both fetal and maternal components) common usage will prevail in this discussion.
A pluriparous Standardbred mare aborted a fetus at approximately 9 months of gestation. This would have been her fourth pregnancy. The foal was in good body condition at presentation and although the placenta was abnormal as discussed below, the fetus itself showed no macroscopic abnormalities.
The placenta and fetus were attached i.e. the fetus and its placenta had been expelled as a unit.
The crown rump length of the fetus was approx 80 cm and its umbilical cord was 66 long with approximately equal intra-amnionic and extra-amnionic lengths. The cord was not excessively twisted and showed no macroscopic abnormalities. Also, the mare had been vaccinated repeatedly against EHV1, as is generally recommended.
Once the fetus and its placenta were cleaned and arranged for inspection, severe placentitis was evident in the placenta that had occupied the body of the uterus. The affected area reached from the cervical star to the bases of the placenta that had occupied the uterine horns. As shown below, a strip of normal placenta was present along the right side of the placenta, adjacent to the area of placentitis.
A clear line of demarcation was present between the healthy and affected areas. It appeared as though an infectious process had begun in the region of the cervical star and had progress cranially and laterally across the body of the chorion. In the image below, the cervical star is barely visible on the right side of the chorion.
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Histology was examined under the yellow ring i.e. an especially thickened, pale and rough area of the affected placenta. This area was completed denuded of villi and disseminated focal, suppurative placentitis was present. This is seen below:
A higher power view of the neutrophilic infiltration is also shown:
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A closer view of the line of demarcation shows healthy chorion (chorioallantois) on the right and the denuded, abnormal chorion on the left. The area under the yellow ring was sampled for histology
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Low power histology of the ringed area is shown below. Normal microcotyledonary placentation can be seen in the sub-image at right. The margin between normal and abnormal tissue is shown in the sub-image on the left. On the extreme left, the villi have been completely destroyed.
Complete destruction of the villi in the margin are is shown below on high power, again with substantial infiltration of neutrophils:
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Interestingly, many collections of spore-like bodies (shown under yellow rings) were present in both the areas of destruction.....
....and in the adjacent areas where villi were still present (see below).
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Paint brush petechia were present on the allantoic surface of the amnion (the allanto-amnion). These areas were not examined histologically. The petechia were presumed to be due to a local inflammatory product from the allantochorion. Histology of the fetal adrenals, lungs, kidney and liver was normal.
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Large vessels present in the amnion (red arrow) were consistent with the immature state of the fetus.
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In an attempt to demonstrate an etiologic agent, tissue sections of the placenta in the areas of chorionic villus destruction were stained with Periodic acid–Schiff (PAS) and later, with Grocott-Gomori's (or Gömöri) methenamine silver stain (GMS). Both of these stains are commonly used to identify fungi and yeasts, especially PAS which is quicker, cheaper and more convenient stain to use than GMS.
Using PAS stain, no etiologic agent could be seen. However GMS showed large populations of yeast-like organisms in the affected areas:
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It was presumed that it was these organisms and smaller forms of the same, that had been identified as "spore-like structures" on the H&E sections discussed earlier in this entry.
Thanks to Dr Peter Sudbery (P.Sudbery@shef.ac.uk) and Dr Mats Troedssen and colleagues at the Gluck institute Ky. for their opinions. These organisms were tentatively identified as yeasts. According to Dr Sudbery, because of their small size and absence of filamentous forms, they are unlikely to be C. albicans.
As shown below (with kind permission of Dr Sudbery) filamentous forms of C. albicans are common.
Image size: 960 x 1999px, copyright Dr Peter Sudbery (P.Sudbery@shef.ac.uk)
A MacDonalds gram stain also revealed the presence of large numbers of Gram positive coccobacilli bacteria deep in the chorion. This indicated that these bacteria were probably not contaminants and were most likely participants in the pathogenesis of placentitis.
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In consultation with a pathologist, it was not possible to say what genus bacteria these were.
Due to the potentially destructive nature of the yeast-like pathogen and the Gram positive bacteria, we have suggested to the mares' owner that an endometrial biopsy should be examined to determine the prognosis for fertility. Also, endometrial cytology should be studied for the continuing presence of pathogens. In the event that the yeast-like organism is still present, a 1% irrigation solution of clotrimazole should be used for treatment. In North America this is compounded for veterinary use (http://www.wedgewoodpetrx.com) and could easily be compounded elsewhere. Antibiotic treatment may also be indicated.
Finally, the cervix of this mare should be examined for tears or any other imperfections that may have contributed to ascending placentitis.
Reference: Sudbery et al. 2004. The distinct morphogenic states of Candida albicans. Trends in microbiology. 12:317-324.
