Swine dysentery

Early signs are partial anorexia and soft yellow to grey faeces containing mucus and flecks of blood, sometimes with fever of 40 to 40.5 degrees C. Diarrhoea becomes watery, with blood, mucus and fibrinous exudate. Prolonged cases show dehydration, weight loss, hollow flanks and slowed growth. At necropsy, lesions are confined to the caecum, colon and rectum: the intestinal wall, mesentery and mesenteric lymph nodes are hyperaemic and oedematous, and mucus, fibrin and blood cover the mucosa, most markedly at the apex of the spiral colon.

Swine dysentery is a mucohaemorrhagic colitis caused by strongly beta-haemolytic Brachyspira species, chiefly Brachyspira hyodysenteriae, with B. hampsonii and B. suanatina also implicated. These Gram-negative, motile, spiral anaerobes rely on chemotaxis and flagellar motility to reach the colonic mucus layer and produce haemolysins and lipooligosaccharide. Acting together with other anaerobes of the large-bowel microbiota, they injure the surface of the caecum and colon: epithelium necroses, mucus is hypersecreted, multifocal haemorrhage and fibrinous exudate form, goblet cells multiply and neutrophils infiltrate the lamina propria. The damaged mucosa can no longer reabsorb fluid, so diarrhoea containing blood and mucus results.

Grower and finisher pigs are mainly affected, weaners less often. Spread is faecal-oral, most often through introduction of subclinical carrier pigs, and indirectly through contaminated transport vehicles, lagoon water and animal vectors. B. hyodysenteriae has been detected in rats, mice, wild birds such as mallards and gulls, feral pigs, dogs, flies and cockroaches, and it survived 78 days in soil containing faeces at 10 degrees C, and up to 112 days in pure pig faeces. Reported prevalence ranges from 0% to nearly 40%. Carriers shed the organism before signs appear, allowing spread before the disease is recognised. Losses come from deaths, antimicrobial costs and poor feed conversion, and diets that deliver more fermentable substrate to the large intestine increase disease.

Colonic spirochaetosis from Brachyspira pilosicoli causes milder green or brown watery to mucoid diarrhoea that may recur. Proliferative enteropathy from Lawsonia intracellularis shows crypt hyperplasia with loss of goblet cells, unlike dysentery. Salmonellosis produces necrotic enterotyphlocolitis extending to the ileum, and culture yields Salmonella. Heavy whipworm (Trichuris suis) infection is also considered. Selective anaerobic culture with PCR or MALDI-TOF identifies the Brachyspira species.

Large intestine: caecum, spiral colon, descending colon, rectum; colonic mucosa and mucus layer; mesentery and mesenteric lymph nodes

Strict quarantine of incoming pigs; all-in/all-out with cleaning and disinfection; rodent and waterfowl control; diets with more soluble fibre (e.g. sugar beet pulp). Vaccines have had limited success.

Mortality 50-90% in severe haemorrhagic cases (Alvarez-Ordonez et al.; Luppi et al.); morbidity can exceed 50% and mortality 30% or more if untreated (MSD). Early antimicrobial treatment is effective, but strains with reduced susceptibility are emerging.