Processionary caterpillar setae and equine fetal loss: 2. Histopathology of the fetal-placental unit from experimentally exposed mares.

This research aims to explore the impact of exposure to the Processionary caterpillar or its exoskeleton on pregnant horses, finding that it may be a significant cause of amnionitis and fetal loss in horses.

Experimental Procedure

• The researchers conducted an experiment involving pregnant mares which were subjected to exposure to either the entire Processionary caterpillar or its exoskeleton. The method of exposure was through gavage, a process where food is administered directly to the stomach.
• The experiment led to certain pregnancies leading to abortions or being near/full term. The resulting tissues from these events, which consisted of aborted fetuses, fetuses from euthanized mares, foals’ membranes, and foals’ organs, were collected and analyzed.
• In addition to these, tissue from control groups unexposed to the caterpillar, including fetus and membranes, were also studied.

Results

• The scientists found that fragments of the caterpillar’s hair, or setae, were present in the allantochorion (fetal membrane functioning to exchange nutrients) of the fetuses from the mares that had been euthanized, and in a majority (92%) of the aborted fetuses.
• The fragments were located in different parts of the placenta, ranging from the cervical pole region to the body that encompasses the umbilical insertion and pregnant horn.
• The numbers of fragments in each fetus varied, ranging from a single fragment to as many as seven.
• The seta were observed in the allantochorion from as early as two days after the initial treatment and remained for up to 22 days.

Pathological Findings

• The study observed acute to chronic active inflammation in all aborted fetuses, euthanized fetuses, and at least one tissue level in the membranes from full-term foals.
• 95% of the examined membranes presented with amnionitis, funisitis, and allantoitis, conditions involving inflammation of different areas of the fetal membranes.
• Pneumonia was present in 95% of the specimens. Furthermore, bacteria was noticed in the tissue of 90.5% of the specimens, with or without accompanying inflammation.

Significance

• The results of this study suggest a clear link between exposure to the Processionary caterpillar or its shed skin and fetal loss in horses, based on the rapid migration of setae.
• This supports the hypothesis that direct migration of setae into the fetal membranes could be a major initiating factor for inflammation of the amnion and subsequent fetal loss.