Infections of the Intestines: Tuberculosis (TB) & Amoebiasis

State the common bacterial infections of the intestines.

1. Secretory diarrhoea

• Vibrio cholerae, enterotoxigenic and enterohaemorrhagic E.coli

• Generally non-invasive

• Secretory diarrhoea with no faecal leucocytes

2. Inflammatory diarrhoea

• Enteroinvasive E.coli, Shigella, Campylobacter, non-typhoidal Salmonella

species

• Readily invade intestinal epithelium

• Provoke intense polymorph reaction

2. Describe the pathological features of tuberculous enteritis. (C2)

• primary infection of small intestines

• Secondary infection of small intestines

• Ilio-caecal tuberculosis

Primary infection

• Inconspicuous intestinal lesion

Gross enlargement of mesenteric lymph nodes

(characteristic of bovine TB in UK, now eliminated through introduction of tubercle-

free herds of cattle and pasteurization of milk)

Describe the pathological features of tuberculous enteritis. (C2)

• primary infection of small intestines

• Secondary infection of small intestines

• Ilio-caecal tuberculosis

Secondary infection

Occur as complication of extensive pulmonary tuberculosis - swallowing infected

sputum

• Ulcer in ileum - typical alimentary lesion

• Ulcers enlarge and follow paths of lymphatic around the circumference of

intestines → encircle the bowel (transverse mucosal ulcers)

• Heals by fibrosis → results in stricture formation in subsequent cicatrisation

• Inflammatory exudate on serosal surface may organize → form fibrous adhesions

Describe the pathological features of tuberculous enteritis. (C2)

• primary infection of small intestines

• Secondary infection of small intestines

• Ilio-caecal tuberculosis

Ilio- caecal tuberculosis

Distinct form of infection

• Ulcerative, granulomatous and fibrotic process occur around ilio-caecal valve

• Variable extension into ileum and caecum

• Thickening and stenosis present picture frequently indistinguishable from

Crohn's disease

• Active intra-intestinal TB can be treated with chemotherapy

• Surgery required for treatment of complications:

• Intestinal obstruction by strictures and adhesions

• Perforation of ulcers and malabsorption due to widespread mucosal

involvement and blockage of lymphatic drainage

Complications of Tuberculous Enteritis

1. Intestinal obstruction due to kinking by adhesions

2. Perforation, with "walled-off" or generalized peritonitis

3. Malabsorption syndrome due to extensive involvement of small bowel and mesenteric

   lymphatics, and enteroenteric fistulae

Pathological features of Amoebiasis in large

intestines

Disease of large intestine

• Causative agent: protozoan Entamoeba histolytica common in subtropical regions; affects 10% world's population

• Mode of spread: faeco-oral transmission of amoebic cysts

• Cysts pass unharmed through stomach; cyst wall dissolved on r

active amoebae released

• Cysts secrete cytolytic enzymes - enables passage through intestine

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Histologically:

• Lead to deep, flask shaped ulcers,

extending into the submucosa

• Architectural distortion of adjacent

mucosa - mimicking ulcerative colitis

Common sites affected

• Caecum and ascending colon - most involved

• Sigmoid colon, rectum and appendix - may be involved

Complications of amoebic enteritis

Complications:

1. Blood spread may result in liver abscesses - potentially fatal complication

2. Rarely abscesses reach lung and heart by direct extension

3. Spread to kidneys and brain via blood spread

Clinical presentation of amoebic enteritis

1. Asymptomatic - present with mild diarrhoea, dysenteric and invasive infection

2. Occasionally present as acute necrotizing colitis and megacolon

• Both associated with significant mortality