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  Discussion on Research: Pathology of Caterpillar Induced Equine Abortion
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DrO

Posted on Thursday, Jan 12, 2017 - 11:47 am:

It has been a while since we have heard much more about caterpillar induced abortion following the 2002 abortion storms. Here are two papers that explore the subject in greater depth than I have seen before. Surprising is the rapidity of the migration of the setae. Note that the setae also reliably caused inflammation of the mare's GI tract including colic and colitis.
DrO


Vet Pathol. 2014 Nov;51(6):1117-30.
Processionary caterpillar setae and equine fetal loss: 1. Histopathology of experimentally exposed pregnant mares.

Todhunter KH1, Cawdell-Smith AJ2, Bryden WL2, Perkins NR 3, Begg AP4.

Author information:
1Equine Research Unit, School of Agriculture and Food Sciences, The University of Queensland, Gatton Queensland, Australia todhunter@westnet.com.au.
2Equine Research Unit, School of Agriculture and Food Sciences, The University of Queensland, Gatton Queensland, Australia.
3Equine Research Unit, School of Agriculture and Food Sciences, The University of Queensland, Gatton Queensland, Australia AusVet Animal Health Services, Toowoomba, Queensland, Australia.
4Vetnostics, North Ryde, New South Wales, Australia.

Abstract

Six pregnant Standardbred mares aged between 6 and 14 years were gavaged with 50 g or 100 g of suspended emulsified whole Processionary caterpillars (Ochrogaster lunifer) for 5 days during 2 experiments undertaken to study the etiology of equine amnionitis and fetal loss (EAFL). The 6 treated mares and 1 untreated mare were between 128 and 252 days gestation. Mare 1 (untreated) was euthanized on day 5 of the treatment period, while the treated mares were euthanized on days 2, 4, 8, 10, 12, and 24 days from their first treatment. Caterpillar setae were not found in the untreated mare. Setal fragments were present in all regions of the gastrointestinal tracts in all treated mares, the uteri and mesenteric lymph nodes of 5 mares, and the liver of 4 mares. Acute gastroenteritis of varying severity was present in all treated mares, and 5 of 6 mares had acute colitis and endometritis. Focal hyperplastic serositis was found in the duodenum, cecum, dorsal colon, and uteri of various mares occasionally with embedded setal fragments. Setal invasion of the mucosa evoked a range of lesions including superficial erosion to deep ulceration. Inflammation in deeper tissues ranged from unapparent to neutrophilic (microabscesses), eosinophilic, or mononuclear (microgranulomas). The finding of setal fragments within the uterus of experimental mares suggests that direct migration of setal fragments acting as a bacterial vector is a likely mechanism for the bacterial abortions that characterize equine amnionitis and fetal loss.

Vet Pathol. 2014 Nov;51(6):1131-42.
Processionary caterpillar setae and equine fetal loss: 2. Histopathology of the fetal-placental unit from experimentally exposed mares.

Todhunter KH1, Cawdell-Smith AJ2, Bryden WL2, Perkins NR3, Begg AP4.

Author information:
1Equine Research Unit, School of Agriculture and Food Sciences, The University of Queensland, Gatton, Queensland, Australia todhunter@westnet.com.au.
2Equine Research Unit, School of Agriculture and Food Sciences, The University of Queensland, Gatton, Queensland, Australia.
3Equine Research Unit, School of Agriculture and Food Sciences, The University of Queensland, Gatton, Queensland, Australia AusVet Animal Health Services, Toowoomba, Queensland, Australia.
4Vetnostics, North Ryde, New South Wales, Australia.

Abstract

Pregnant mares were experimentally exposed to whole caterpillar or exoskeleton of the Processionary caterpillar (Ochrogaster lunifer) via gavage. Tissues were collected from resulting abortions and near or full-term pregnancies consisting of 13 aborted fetuses, 3 fetuses from treated euthanized mares, membranes of 5 foals, and organs from 3 foals. Three control membranes and 1 control fetus and membranes were examined. Caterpillar setal fragments were present in the allantochorion of the 3 fetuses from the euthanized mares and 11 of 12 aborted fetuses (92%) embedded in the chorion (villi or stroma) or allantois (vasculature or stroma). Placental locations of fragments ranged from the cervical pole region to the body encompassing the umbilical insertion and pregnant horn. Numbers in each fetus ranged from 1 to 7 fragments. Setae were present in the allantochorion from 2 to 22 days after the initial treatment. Acute to chronic active inflammation was present in all aborted fetuses, all euthanized fetuses, and within at least 1 tissue level (chorion, allantois, umbilical cord, or amnion) of the membranes from full-term foals. Amnionitis, funisitis, and allantoitis were present in 95% of the examined membranes. Pneumonia was present in 95% of the specimens, and bacteria were present histologically in 90.5% of the specimens with or without accompanying inflammation. The rapid migration of setae within 2 days after mare exposure suggests that direct setal migration into the fetal membranes is a likely initiating factor for equine amnionitis and fetal loss (EAFL).
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