Signalment:  

Two age-unknown (post-weaning) female and castrated male Norwegian Landrace pigs, (Sus scrofa domestics).Two pigs were received for necropsy from a farm with diarrhea among weaned pigs.

Gross Description:  

The nutritional status of both pigs was slightly below normal. Feces in the large bowel of both pigs had looser consistency than normal, but the cecum and colon were otherwise normal macroscopically. One of the pigs had slightly enlarged mesenteric lymph nodes. 

Histopathologic Description:

Histologic findings were similar in colon and cecum from one pig (13/226) and colon from the other pig (13/227). Surface epithelium was multifocally attenuated, and variably covered by numerous bacteria. Numerous crypts contained abundant bacteria with a morphology consistent with spirochetes. Number of goblet cells in crypt epithelium varied from few to moderate, but was generally decreased. Some crypts contained abundant neutrophils (crypt abscesses), and some crypts were lined by flattened attenuated epithelial cells. The lamina propria contained a moderate increase in lymphocytes and macrophages and few neutrophils. 

In the deeper parts of some crypts (moderate numbers in the colon of pig 13/226, and few in the cecum from pig 13/226 and colon from pig 13/227) there were luminal pyriform to crescent-shaped organisms, approximately 5 x 7 μm in size, with a faint nucleus and eosinophilic cytoplasm (consistent with trichomonads). 

In a few sections there were also a few ciliated large protozoa (Balantidium coli) on the surface of the mucosa (incidental finding). 

Morphologic Diagnosis:  

Cecum and colon: Typhlocolitis, catarrhal, diffuse, mild with moderate numbers of crypt abscesses, high numbers of intracryptal spirochetes and moderate numbers of intracryptal trichomonads and few surface ciliated large protozoa. 

Lab Results:  

From colons of both pigs a mixed bacterial growth with Brachyspira sp. was cultured and from both pigs the Brachyspira sp. were identified as Brachyspira pilosicoli. 

Condition:  

Brachyspira pilosicoli

Contributor Comment:  

Two members of the genus Brachyspira may cause colitis in swine: the strongly hemolytic Brachyspira hyodysenteriae which is the cause of swine dysentery, and the weakly hemolytic B. pilosicoli which is the cause of porcine intestinal spirochetosis.(1,3) B. pilosicoli has a wide host range, is capable of infecting a number of animal species, both mammals and birds, and may also be zoonotic.(1) Other weakly hemolytic members of the Brachyspira genus that may be isolated from swine, B. innocens, B. intermedia and B. murdochii, have not been shown to cause disease in experimentally infected conventional pigs and are considered to be nonpathogenic commensals in pigs.(3) While swine dysentery is a highly infectious disease of mainly weaned pigs characterized by a large bowel diarrhea with mucus, blood, or fibrin in the feces, porcine intestinal spirochetosis is typically a milder disease characterized by transient watery to mucoid diarrhea without blood,(1) as was seen in these two pigs. The histologic findings are focal erosions, slight edema, crypt abscesses, mild infiltrate of mononuclear cells in lamina propria and the spirochetes may be found attached to surface epithelium, inside dilated crypts, invading through tight junctions between colonic enterocytes, within goblet cells, and within the lamina propria.(3,4)

The protozoal organisms located in colonic crypts were interpreted as trichomonads. Tritrichomonas suis is considered to be an apathogenic commensal in pigs that may colonize nasal cavity and intestines of pigs. This species has been found to be identical in sequence to T. foetus,(2,7) a venereally transmitted pathogen that affects cattle; however, other trichomonads may also be identified in fecal samples from pigs, such as Tetratrichomonas buttreyi,(6) Trichomitus rotunda and others unrelated to previously described trichomonads.(5)

JPC Diagnosis:  

Colon: Colitis, necrotizing, subacute, diffuse, moderate, with marked crypt hyperplasia.

Conference Comment:  

Conference participants conducted a brief discussion of the differential diagnosis for the clinical, gross and histological findings in this case, including Brachyspira hyodysenteriae, Lawsonia intracellularis, Salmonella spp., Clostridium spp., Escherichia coli, Trichuris suis, coronavirus and rotavirus. As noted by the contributor, B. hyodystenteriae is strongly beta-hemolytic and highly infectious, causing severe hemorrhagic diarrhea and fibrinonecrotic pseudomembranous colitis in affected swine. Although virulence factors are poorly defined, both B. dysenteriae and B. pilosicoli are thought to be chemotactically attracted to intestinal mucin and tend to be intimately associated with the intestinal mucus layer. Lawsonia intracellularis, on the other hand, is an obligate intracellular gram-negative bacterium that colonizes enterocytes in the ileum and colon, resulting in proliferative to necrotizing enteritis/colitis. Salmonella spp. are important enteric pathogens of swine.  S. typhimurium causes acute/chronic enterocolitis in feeder pigs; it has also been associated with necrotizing proctitis and subsequent rectal stricture. The major clinical manifestation of S. cholerasuis is septicemia with secondary endothelial damage. Common microscopic findings include interstitial pneumonia, multiple foci of hepatic necrosis (paratyphoid nodules), renal cortical microhemorrhages (turkey egg kidney), polyarthritis or polysynovitis, meningoencephalomyelitis and enterocolitis, often with colonic button ulcers.(1)

C. perfringens type C is associated with outbreaks of necrohemorrhagic enteritis in suckling piglets, while C. difficile is recognized as a cause of fibrinous typhlocolitis and mesocolonic edema in neonatal piglets see ( WSC 2013-2014, conference 17, case 1 for a more detailed discussion of Clostridium spp.). Enterotoxigenic E. coli (ETEC) causes profuse watery diarrhea in neonatal piglets via heat-labile (LTI and LTII) and heat-stable (STa and STb) enterotoxins (see WSC 2013-2014, conference 12, case 2 for a more detailed discussion of E. coli); however, histological changes are typically minimal. Enteropathogenic (attaching and effacing) E. coli is a less frequently reported cause of diarrhea in swine, and, although an uncommon manifestation, enteritis has also been associated with some strains of enterohemorrhagic, Shiga-like toxin producing E. coli, the cause of porcine edema disease. The whipworm Trichuris suis inhabits the cecum and colon of swine, where it embeds in the surface epithelium; severe infections may lead to mucohemorrhagic typhlocolitis.(1)

There are two coronaviruses associated with porcine diarrhea. Transmissible gastroenteritis (TGE) is a highly contagious disease that is most severe in piglets younger than 10 days of age, characterized by high morbidity with vomiting and profuse diarrhea. The causative agent, a group 1 porcine coronavirus, destroys intestinal villar epithelial cells, resulting in marked villar atrophy and diarrhea secondary to malabsorption. Porcine epidemic diarrhea (PED) virus is another group 1 coronavirus that causes similar, though less severe signs in older pigs. The PED virus is endemic in many Asian countries, and has been present in Europe since the early 1970s; however, until recently (i.e., May 2013), it was not present in the United States, and its emergence has caused epidemic disease with important economic implications for the American pork industry. Rotavirus is enzootic in many swine herds and causes villar atrophy with ensuing diarrhea in both suckling and weaned pigs, although it is generally less severe than TGE. Finally, porcine adenoviral inclusions have been identified within small intestinal enterocytes in both asymptomatic pigs and those presenting with watery diarrhea; however, the significance of this finding remains controversial, and adenoviral infection is not yet recognized as a significant cause of enteric disease in swine.(1)

In this case, histochemical staining with Warthin-Starry highlights numerous argyrophilic spirochetes adhered to the enteric mucosa, supporting a diagnosis of colonic spirochetosis, while the culture results as reported by the contributor definitively identify the etiologic agent as Brachyspira pilosicoli.

References:

1. Brown CC, Baker DC, Barker IK. Alimentary system. In: Maxie MG, ed. Jubb, Kennedy and Palmer's Pathology of Domestic Animals. Vol. 2. 5th ed. Philadelphia, PA: Elsevier; 2007:3-296.

2. Frey CF, Muller N. Tritrichomonas- systematics of an enigmatic genus. Mol Cell Probes. 2012;26:132-136.

3. Hampson DJ, Duhamel GE. Porcine colonic spirochetosis / intestinal spirochetosis. In: Straw BE, Zimmerman JJ, D'Allaire S, Taylor DJ, eds. Diseases of swine. Oxford, UK: Blackwell Publishing; 2006:755-783. 

4. Jensen TK, Moller K, Boye M, Leser TD, Jorsal SE. Scanning electron microscopy and fluorescent in situ hybridization of experimental Brachyspira (Serpulina) pilosicoli infection in growing pigs. Vet Pathol. 2000;37:22-32.

5. Mostegl MM, Richter B, Nedorost N, Lang C, Maderner A, Dinhopl N, et al. First evidence of previously undescribed trichomonad species in the intestine of pigs? Vet Parasitol. 2012;185:86-90.

6. Rivera WL, Lupisan AJ, Baking JM. Ultrastructural study of a tetratrichomonad isolated from pig fecal samples. Parasitol Res. 2008;103:1311-1316.

7. Tachezy J, Tachezy R, Hampl V, Sedinova M, Vanacova S, Vrlik M, et al. Pathogen Tritrichomonas foetus (Riedmuller, 1928) and pig commensal Tritrichomonas suis (Gruby & Delafond, 1843) belong to the same species. J Eukaryot Microbiol. 2002;49:154-163.

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2-1. Colon

2-2. Colon

2-3. Colon

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