A series of abortions occurred in mares in New South Wales during 2004 that involved unusual bacteria and unique lesions on post mortem examination of aborted foetuses and foetal membranes. Investigations ensued to determine the cause of the abortions and the condition was termed Equine Amnionitis and Foetal Loss (EAFL). Studies within this body of work detail the histopathology and outline the bacteria associated with the clinical cases of EAFL. A detailed working case definition for EAFL is also given. An epidemiological association was found between the abortions and the presence of the Processionary caterpillar (Ochrogaster lunifer) leading to experimental studies involving the exposure of mid-term pregnant mares to the exoskeleton or whole Processionary caterpillar. The experiments involved nasogastric exposure with suspended emulsified caterpillar exoskeleton (1g, 3g, and 5g) or emulsified suspended whole caterpillar (50g, 100g) for 5 days. The histopathology of 1 untreated and six treated mares and the resulting abortions, euthanized foetuses, or compromised foals were examined in these studies to determine the effect of oral exposure to processionary caterpillars. The treated mares were selected from the two experiments involving whole caterpillars and euthanized on sequential days of 2, 4, 8, 10, 12, and 24 from the first treatment. The euthanized foetuses, abortions, stillborn and compromised foals resulting from all three experiments were also examined. Setal fragments were present in all regions of the gastrointestinal tracts in all treated mares, the uteri and mesenteric lymph nodes of five mares and within the liver of four mares. Acute gastroenteritis of varying severity was present in all treated mares with five of six mares have 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. Cellular reactions in deeper tissues ranged from unapparent to neutrophilic (microabscesses), eosinophilic, or mononuclear (microgranulomas). Caterpillar setal fragments were present in the allantochorion of the 3 foetuses from the euthanized mares and 11 of 12 aborted foetuses either 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 foetus ranged from 1 to 7 fragments. Setae were present in the allantochorion from 2 to 22 days after the initial treatment. A wide range of inflammation from subtle acute to chronic active was present in all aborted foetuses; all euthanized foetuses, and within at least 1 tissue level (chorion, allantois, umbilical cord, or amnion) of the membranes from full term compromised 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. A wide variety of bacteria were isolated from the foetuses including novel Streptococci and environmental coryneforms similar to clinical cases of EAFL. Setal fragments were found within the uterus of experimental mares and the allantochorion of aborted and euthanized foetuses as quickly as 2 days post-exposure in addition to the isolation of enteric or environmental bacteria from lung and stomach contents of aborted foetuses.
An additional experiment exposing mares in the pre-placentation stage (<45 days) or early placentation stage (45-90 days) of pregnancy resulted in the induction of two cases of focal mucoid placentitis. The histopathology of these cases are detailed in addition to two cases of focal mucoid placentitis in confirmed EAFL field cases with the characteristic histologic lesions similar to Nocardioform placentitis but with the isolation of a variety of bacteria. The induction of focal mucoid placentitis after exposure of mares in the early stages of pregnancy combined with the knowledge that caterpillar setae migrate into the uterus and allantochorion of exposed mares suggests that focal mucoid placentitis is yet another manifestation of EAFL.
Detailed experience in identifying the appearance of setal fragments which is highlighted under toluidine blue staining allowed in depth examination of tissues from equine abortions submitted for examination in 2012. Five cases were found in which a caterpillar setal fragment was found in the allantochorion confirming that setal fragments migrate from field exposure as well as experimental exposure to processionary caterpillars.
The experiments in this thesis have shown histologically for the first time, the ability of Processionary caterpillar setae to penetrate the maternal gut wall and migrate directly into the uterus and placental tissues. This is considered to be the most likely means of translocation of bacteria to the foetal membranes. The direct, rapid migration of setae in as little as two days from ingestion from the gut to the placenta facilitates bacterial infection. Bacteria present in the mare’s gut likely attach to migrating setal fragments and translocate through the gut wall, the uterus and the foetal membranes in which they subsequently colonize. Incomplete migration of setal fragments may account for the focal mucoid placentitis induced when mares were exposed in early gestation. Bacterial colonization of the foetal membranes and/or foetus may cause foetal compromise or death and eventual abortion.
The variety of manifestations of EAFL due to the migration of setal fragments ranging from acute abortion, chronic active placentitis, stillbirth, compromised preterm and full term foals, and focal mucoid placentitis have a significant impact on the breeding of horses and ultimately the racing industry in Australia.