Processionary caterpillar setae and equine fetal loss: 1. Histopathology of experimentally exposed pregnant mares.

The research article discusses a study where six pregnant horses were exposed to Processionary caterpillars to understand their role in causing equine amnionitis and fetal loss – a condition that leads to abortion in horses.

Experiment Overview

• The researchers selected six pregnant Standardbred mares between the ages of 6 and 14 for the experiment. An additional mare, left untreated, served as a control.
• The mares received a dose of 50g or 100g of Processionary caterpillars daily for five days, and their gestation period ranged between 128 and 252 days.
• The untreated mare was euthanized on day 5 of the experiment, while the treated mares were euthanized at different intervals after their first exposure to the caterpillars. This allowed the researchers to examine the progression of the condition over time.

Observations and Findings

• In the untreated mare, no fragments of caterpillar setae (bristles) were found. However, in the treated mares, these fragments were present in various parts of the body, including the gastrointestinal tracts, uteri, mesenteric lymph nodes, and the liver.
• All treated mares displayed various degrees of acute gastroenteritis, and five out of six mares showed signs of acute colitis and endometritis.
• The researchers also found evidence of focal hyperplastic serositis, an inflammatory condition, in some of the treated mares.
• The caterpillar setae proved damaging to the mucosa, causing various levels of damage, from superficial erosion to deep ulceration. It also caused inflammation in deeper tissues, with different cellular responses depending on the mare.

Conclusion and Implications

• The presence of setal fragments within the uterus of the treated mares suggests that these fragments likely play a direct role in bacterial abortions characteristic of equine amnionitis and fetal loss.
• The follow-up implication is that these caterpillar setae, acting as a bacterial vector, may be directly responsible for this condition among horses. This insight could pave the way for appropriate preventive measures and treatments.