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.
