Bowel Infection

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Infective disorders of the bowel are common and  are due to many classes of organism.

  Viruses: rotaviruses cause 50% of infantile diarrhoea and account for some adult cases. Norwalk viruses acount for 30% of adult cases of gastroenteritis.

  Bacteria: some bacteria cause direct damage to thebowel (e.g. Salmonella typhi and Campylobacter jejuni), while others produce enterotoxins (e.g. in salmonellosis and enteropathogenic E. coli).
Tuberculosis may affect the gut, particularly the terminal ileum.
Yersinia infection may cause ulceration and ileitis.
Campylobacter infection is the commonest cause of bacterial diarrhoea mainly affecting  the colon.

  Protozoa: Giardia causes infection of the small bowel  and gives rise to a malabsorption syndrome.Cryptosporidia and microsporidia may cause disease, particularly in immunosuppressed patients.

  Fungi: infection is virtually restricted to   immunosuppressed patients.

  Helminths: parasitization of the bowel by helminths is widespread, especially in the tropics. Many of the clinical problems are caused by immune-mediated hypersensitivity causing hypereosinophilia syndromes.

Gastrointestinal infections are common in immunosuppressed patients, particularly with AIDS.
Most patients with AIDS have chronic diarrhoea which can be caused by a wide range of pathogens.

Several bacterial infections of the gut cause infection by invasion of the mucosa. Many cause diarrhoea with blood and pus in the stool, termed bacterial dysentery. The main organisms causing this type of infection are:

  Campylobacter invades mucosa in the jejunum, ileum and colon, causing ulceration and acute inflammation.

  Salmonella typhi, S. paratyphi A, B, and C are transmitted in food and water contaminated by the faeces or urine of a carrier.
In S.typhi infection organisms initially proliferate in the reticuloendothelial system. A secondary bacteraemia develops and Peyer's patches become ulcerated.
Patients develop fever, diarrhoea, splenomegaly (75%), and a skin rash consisting of rose   spots (50%).

  Shigella infections are mainly seen in young children. The organism invades mucosa of the colon and distal ileum causing mucosal ulceration, most marked in the sigmoid colon and rectum.

Most cases of intestinal tuberculosis are caused by ingestion of bacteria in food.
The disease particularly affects the terminal ileum and caecum.

Whipple's disease is a rare condition caused by infection by an actinomycete called Tropheryma whippelii.
 
It is a multisystem disorder with malabsorption due to small bowel involvement, lymphadenopathy, arthritis and CNS symptoms.

Some bacteria produce enterotoxins and cause disease without invasion Bacterial enterotoxins cause disease in two
circumstances.

In the first, the toxin is formed in the food before it is eaten, resulting in
vomiting and diarrhoea about 12 hours after ingestion (e.g. staphylococcal food poisoning).

In the second, the bacteria proliferate in the gut after ingestion and produce toxins which then cause intestinal disturbance; this extra growth stage means that the disease takes about 24 hours to develop after contaminated food is eaten.

Salmonella enteritidis, S. typhimurium, S. hadar, S. virchow produce enterotoxin-induced fluid and electrolyte disturbance. Incubation is 24-48 hours, resulting in an enterocolitis with profuse diarrhoea and vomiting lasting about 48 hours.

Vibrio cholerae is acquired through water contaminated with faeces.
Organisms grow in the small bowel and secrete a toxin which causes uncontrolled cAMP-stimulated secretion of fluid into the gut producing severe watery diarrhoea.

Pseudomembranous enterocolitis is caused by a clostridial toxin causing mucosal necrosis

In pseudomembranous colitis, Clostridium difficile overgrowth produces an enterotoxin that results in necrosis of the colonic mucosa.

The condition is almost invariably associated with antibiotic therapy, but other diseases of the colon which allow clostridial overgrowth, also predispose to its development (gastrointestinal surgery, ischaemia, shock, burns).
Patients develop fever, abdominal pain and diarrhoea.

Colon showing small areas of superficial ulceration typical of pseudomembranous enterocolitis.
 
The appearance is likened to 'paint splashes'.

Important protozoans causing bowel infection are Giardia, Cryptosporidium and Entamoeba

The most important protozoa causing gut infection are:

  Giardia lamblia, which is a flagellate protozoan acquired  from contaminated water. It infects the duodenum and
   upper jejunum and may cause diarrhoea, abdominal pain,  weight loss, or malabsorption.

  Cryptosporidium parvum, which is acquired from  contaminated water causing a self-limiting diarrhoeal
   illness which may be severe in patients with AIDS.

  Entamoeba histolytica, which is acquired through water or food contaminated by cysts and causes amoebic colitis.

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