Abstract

Pseudomembranous enterocolitis due to Clostridium difficile has been identified in a number of terrestrial mammals, including humans, nonhuman primates, hamsters, rabbits, pigs, horses and guinea pigs. In captive and wild marine mammals clostridial enterocolitis is sporadically recognized and has generally been attributed to Clostridium perfringens enterotoxaemia. This case series characterizes a hemorrhagic enterocolitis in neonatal and juvenile harbor seals (Phoca vitulina) putatively associated with Clostridium difficile toxin A and toxin B.

Over the course of the last 10 years, 15 apparently healthy neonatal and juvenile harbor seals presented to local rehabilitation facilities have either died peracutely with no overt premonitory signs, or had an acute onset of lethargy, depression and dehydration, that rapidly progressed to death. Animals featured segmental to diffuse hemorrhagic enterocolitis characterized by dark red to pink mucoid intestinal contents that were frequently admixed with variably amounts of fibrin. In more severely affected segments of intestine, the mucosa was diffusely dark red, friable, and frequently featured miliary punctate foci of acute hemorrhage. There was mild to moderate transmural edema and occasional hemorrhage with pronounced injection of the serosal vasculature. Mesenteric lymph nodes were enlarged, grey black, and glistening on sectioned surfaces. Histopathology revealed superficial to near full thickness necrosis of the mucosa with intermittent fibrin pseudomembrane formation. The lamina propria had variable congestion with multifocal hemorrhage. Microscopically, these alterations were consistent with Clostridium difficile and certain strains of Escherichia coli, possibly exacerbated by agonal shock. Aerobic and anaerobic culture of multiple levels of bowel have yielded variable, often mixed growth of Escherichia coli, Enterococcus spp, Pseudomonas spp, Aeromonas spp, and Cl. perfringens. Multiplex gene sequence analysis of select E. coli and Cl. perfringens isolates has either been unremarkable or failed to consistently identify toxin-specific genes.

In the summer of 2003, segments of bowel from 5 affected and 5 age-matched controls that succumbed to other, unrelated non-gastrointestinal disease processes were harvested. Ingesta was evaluated by an enzyme immunoassay for the detection of Clostridium difficile toxin A and B in ingesta samples (Premier^TM Meridian Bioscience, Inc, Cincinnati, OH) and proved positive in all the affected, and negative in all unaffected animals. In a small percentage of animals Cl. difficile is part of the normal intestinal flora and toxin production is thought to be associated with antimicrobial administration and disruption of the normal intestinal flora. In wild animals and select captive seals, there was no history of antibiotic administration and the precise pathogenesis of this condition in harbor seals remains unknown. Efforts are underway to further characterize the clinical and pathologic features of this condition.