Signalment:  

Juvenile, weaned harbor seal (Phoca vitulina)Over the course of the last 10 years, 20 apparently healthy neonatal and juvenile harbor seals presented to local rehabilitation facilities having either died peracutely with no overt premonitory signs, or had an acute onset of lethargy, depression and dehydration, that rapidly progressed to death.

In this case, the animal had presented to rehabilitation as a neonate in late August, 2007, had been apparently normal for 4 weeks, and fed a herring-based formula. The animal presented acutely moribund, inappetant, unresponsive, and died.

Gross Description:  

On necropsy, this animal featured segmental to diffuse hemorrhagic enterocolitis characterized by dark red to pink mucoid intestinal contents that were frequently admixed with variable amounts of fibrin. In more severely affected segments of bowel, the mucosa was diffusely dark red, friable, and frequently featured miliary punctuate foci of acute hemorrhage. Mesenteric lymph nodes were enlarged, grey black, and glistening on sectioned surfaces.

Histopathologic Description:

Along varying levels of bowel revealed superficial to near full thickness necrosis of the mucosa with segmental to diffuse fibrin pseudomembrane formation. The lamina propria had variable congestion with multifocal hemorrhage and occasional scattered neutrophils.

Morphologic Diagnosis:  

Intestine: Enteritis, fibrinous and erosive, marked, multifocal to segmental, presumptively due to Clostridium difficile

Condition:  

Clostridium difficile

Contributor Comment:  

In this case, aerobic and anaerobic culture of multiple levels of bowel yielded mixed growth of Escherichia coli, Enterococcus spp, and Pseudomonas spp. Culture with selective media isolated Clostridium difficile, and ingesta was positive for Clostridium difficile toxin A and B (ELISA, Premier TM Meridian Bioscience, Inc., Cincinnati, OH). Microscopically, these enteric lesions are consistent with a variety of bacterial pathogens, including Salmonella spp, Clostridium perfringens, Clostridium difficile, and strains of Escherichia coli, possibly exacerbated by agonal shock (peracute ischemia may present with similar mucosal changes). In human and veterinary medicine, many clostridial infections are polymicrobial and it is difficult to resolve their contribution to the pathogenesis of the lesions. Further microscopic characterization and possible in vitro studies or use of ligated bowel may assist in resolving the role of this pathogen in clinical disease.

Members of the genus Clostridium are considered ubiquitous within the environment, often associated with detritus, soil, ocean sediment, and as a component of the gastrointestinal tract flora of humans and other vertebrates. Many infections are considered endogenous. In humans, foals and piglets, this pathogen is associated with antibiotic associated diarrhea and pseudomembranous colitis and infection may be mild and self limiting or fatal due to enterocolitis. It is important to note that toxin positive animals may not exhibit signs or lesions and lab results should be correlated clinically and pathologically.

Even if this is not considered a significant pathogen from the host perspective, harbor seals in rehabilitation facilities may function as multiplying species for a potential zoonotic pathogen and staff should be appropriately educated about hygienic practices. The culture from this animal, and isolates from 4 other post mortem cases were forwarded to the CDC, Atlanta, Georgia and the more virulent form of this bacteria, strain 027, was not detected by molecular screening.

JPC Diagnosis:  

Small intestine, villi: Necrosis, acute, diffuse, with myriad bacilli

Conference Comment:  

Clostridium difficile causes pseudomembranous colitis in primates, and enteritis and/or colitis in many other species. Disease is usually associated with an imbalance in the intestinal flora and clostridial overgrowth secondary to antibiotics, stress or a change in feed.(1) In horses, C. difficile causes proximal enteritis and hemorrhagic enteritis in foals, and colitis in horses of all ages. Colitis X is an acute colitis in horses that is often attributed to Clostridium perfringens type A, or less commonly C. difficile.(1) In neonatal pigs, C. difficile causes fibrinous typhlocolitis with volcanic ulcers, and scrotal edema, hydrothorax and edema of the mesocolon similar to seen with Edema disease.(1) C. difficile causes disease in a variety of laboratory animals, but is most significant in the guinea pig where it results in antibioticassociated dysbacteriosis. Although C. difficile can cause diarrhea in rabbits, the most common clostridial pathogen associated with the enteritis complex in juvenile rabbits is Clostridium spiroforme.(3)

C. difficile produces two major toxins: toxin A and toxin B. Toxin A is an enterotoxin that stimulates chemokine production, which attracts leukocytes. Toxin B is a cytotoxin that modulates cellular signaling pathways, induces cytokine production and causes apoptosis.(4,6)

References:

1. Brown CC, Baker DC, Barker IK: Alimentary system. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 5th ed., vol. 2, pp. 221. Saunders, Edinburgh, Scotland, 2007
2. Hammitt MC, Bueschel DM, Keel MK, GLock RD, Cuneo P, DeYoung DW, Reggiardo C, Songer JG: A possible role for Clostridium difficile in the etiology of calf enteritis. Vet Microbiol. 127:343-352, 2007
3. Percy DH, Barthold SW: Pathology of Laboratory Rodents and Rabbits, 3rd ed., pp. 225, 268. Blackwell Publishing, Ames, Iowa, 2007
4. McAdam AJ, Sharpe AH: Infectious Diseases. In: Pathological Basis of Disease, eds. Kumar V, Abbas AK, Fausto N, 7th ed., p. 394. Elsevier Saunders, Philadelphia, PA, 2005
5. Merck Veterinary Manual, 9th ed. Aiello S, Ed, Stoskopf M, Contributor Exotic and Laboratory Animals: Marine Mammals. Merck & Co, Inc., 2006
6. Liu C, Crawford JM: The gastrointestinal tract. In: Pathological Basis of Disease, eds. Kumar V, Abbas AK, Fausto N, 7th ed., pp. 836-838. Elsevier Saunders, Philadelphia, PA, 2005
7. Rodriques-Palacios A, Stampfli HR, Duffield T, Peregrine AS, Trotz-Williams KA, Arroyo LG, Brazier JS, Wese JS. Clostridium difficile PCR ribotypes in calves. Canada Emerg. Infect. Dis. 12:1730-1736, 2006