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infects the large intestine and is found
mainly in developing countries. It is transmitted by the faecal-oral
route. The organism causes disease through production of cysteine
protease and amoebapore, an epithelial cytotoxin. It is morphologically
identical to E. dispar, which does not cause disease.
The onset is insidious with little systemic upset: the patient is
ambulant but passes frequent small-volume, offensive, bloody
stools. Abscesses may develop in the liver or, more rarely, abdomen,
lung or brain.
- Rectal ulceration is seen on sigmoidoscopy.
- Trophozoites are demonstrated in ulcer biopsies.
- Three stool specimens for microscopy, antigen detection and
nucleic acid amplification test (NAAT).
- CT and ultrasound for abscesses.
- Serology - may detect liver abscess, but not intestinal
Prevention and control
- Metronidazole for intestinal infection and abscess.
- Diloxanide furoate or paromomycin kills the chronic cyst stage.
Steps to ensure that water is boiled and food adequately cooked
will reduce the risk of amoebic infection.
infection occurs worldwide where poor sanitation
allows water supplies or food to be contaminated with cysts from
human or animal faeces.
Trophozoites multiply in the jejunum and attach to the intestinal
wall by a sucking disk. The mechanism for Giardia diarrhoea
uncertain and may relate to induced apoptosis. Giardial cysts
excreted in the faeces and survive well in the environment.
These may include:
- bulky, offensive, fatty stools;
- anorexia, crampy abdominal pain, borborygmi and flatus;
- weight loss;
- lactose intolerance or fat malabsorption;
- recurrent attacks of infection in patients with IgA deficiency.
- Three concentrated stool samples for microscopy.
- Aspirated jejunal contents can be examined for motile
- Enzyme immunoassay (EIA) and NAAT methods are more sensitive
Metronidazole or tinidazole are used. New therapeutic options
include albendazole and nitazoxanide. Secondary malabsorption
and vitamin deficiency may require investigation and treatment.
Infection occurs in subtropical and tropical regions from contaminated
water supplies; outbreaks from imported soft fruit and fresh
herbs have been reported.
Cyclospora are found inside vacuoles within the epithelium of the
jejunum. There is inflammation, villous atrophy and crypt hyperplasia
leading to malabsorption of vitamin B12, folate, fat and
Diagnosis and Treatment
- Infection takes the form of watery diarrhoea.
- A 'flu-like illness and weight loss may also occur.
- Infection is self-limiting, but may last for weeks with continuing
fatigue, anorexia and weight loss.
- A prolonged, severe, relapsing disease occurs in individuals who
- Microscopy for oocysts in stools.
- NAAT methods are available.
- Co-trimoxazole is an effective treatment, with nitazoxanide as
Cryptosporidium parvum is a zoonotic coccidian parasite that is
transmitted by milk, water and direct contact with farm animals.
It is naturally resistant to chemical disinfectants, surviving water
purification. Person-to-person spread can occur with intimate
contact. Infection is common in children and individuals with
AIDS. It may interfere with the glucose-stimulated sodium pump
in the small intestine, leading to fluid secretion.
Diagnosis and Treatment
- Infection usually produces self-limiting, watery diarrhoea with
- Profuse, prolonged diarrhoea in immunocompromised individuals
may cause life-threatening fluid and electrolyte imbalance.
- Biliary tree, gallbladder and respiratory tract involvement may
- Demonstration of cysts by microscopy.
- Antigen detection or NAAT.
- Nitazoxanide may improve clearance of pathogens but Management
should aim to reverse immunodeficiency (e.g. treatment of
Closely related to Cryptosporidium, Isospora belli presents with a
similar clinical picture, usually following tropical travel. Diagnosis
is by microscopy of stool. Treatment is with co-trimoxazole; fluoroquinolones
These are small intracellular protozoa that infect insects, plants
and animals. Enterocytozoon bieneusi, Encephalitozoon cuniculi,
Encephalitozoon hellem, Septata intestinalis, Pleistophora and
Nosema have been implicated in human infection, usually in
Enterocytozoon bieneusi and S. intestinalis infect epithelial cells of
the small bowel and are associated with diarrhoea. E. cuniculi
infects macrophages, epithelial cells and vascular endothelial cells
in the brain and the kidney plus renal tubular cells. It is associated
with hepatitis, peritonitis, diarrhoea, seizures and disseminated
infection. Before the advent of HIV infection, microsporidia infection
was very rare.
Diagnosis and Treatment
Microscopy using fast trichrome, calcofluor white and Ziehl-
Neelsen stains can be used. Sensitive NAATs are available to