6. Protozoal and Helminthic Infections of the Gastrointestinal Tract Flashcards
What is the method of transmission of intestinal protozoa and helminths?
Faecal-derived materials
Acquired during ingestion of contaminated food or water
Presentation of intestinal protozoa and helminths?
Acute to chronic diarrhoea and inflammation
Name protozoal infection of the GIT, 2 in SI and 1 in colon?
SI: GIardia lambda, crytosporidium parvum
LI: Entamoeba histolytic
Describe the 2 stages of the life cycle of G. lamblia?
- Trophozoite
- Flagellated and bi-nucleated
- Lives in upper part of SI
- Adheres to brush border of epithelial cells - Cyst
- Formed when trophozoite forms resistant wall
- Passes out in stools
- Can survive for several weeks
Pathogenesis of G. lamblia?
Present in duodenum, jejunum and upper ileum
Attaches to the mucosa via ventral sucker
Does not penetrate the surface
Causes damage to the mucosa and villous atrophy
Leads to malabsorption of food, esp. fats and fat soluble vitamins
May swim up bile duct to gall bladder
Clinical presentation of G. lamblia?
Mild infections = asymptomatic
Chronic diarrhoea presents in immunocompromised patients
Stools are characteristically loose, foul-smelling and fatty
C. parvum, transmission and reservoir?
Transmission: Faecally contaminated drinking water
Reservoir: Animals (usually cattle)
Life cycle of C. parvum?
Asexual & sexual development
within host:
• Ingestion of resistant oocysts
• Release of infective sporozoites in small intestine
• Invasion of intestinal epithelium
• Division to form merozoites which re-infect cells
• After sexual phase, oocytes released
Pathogenesis of C. parvum?
- Enters cells of the microvillus border ofsmall intestine
- Remains within vacuole of epithelial cell
- May multiply to give large numbers of progeny, especially in immunocompromised hosts
Presentation of C. parvum?
- Moderate to severe profuse diarrhoea
- Up to 25 litres of watery faeces / day
- Usually self limiting disease
- In HIV positive individuals with CD4+ T-cell counts of <100/mm3, diarrhoea is prolonged and may become irreversible and life- threatening
E. histolytica:
Transmission?
Role of cysts?
Transmission: Ingestion of contaminated food/water, anal sexual activity
Role of cysts:
• Cysts pass through stomach and excyst (break open and release contents) in the small intestine giving rise to progeny
• These adhere to epithelial cells and cause damage mainly through cytolysis
• After mucosal invasion, cysts invade red blood cells giving rise to amoebic colitis
• Trophozoite stages live in large intestine and pass out as resistant, infective cysts
Pathogenesis of E. histolytica?
• Adheres to epithelium and acute
inflammatory cells
• Resists host humoral and cell mediated immune defence mechanisms
• Produces hydrolytic enzymes, proteinases, collagenase, elastase
• Produces protein that lyses neutrophils, the contents of which are toxic to the host
Clinical presentation fo E. histolytica?
- Small localised superficial ulcers leading to mild diarrhoea
- Entire colonic mucosa may become deeply ulcerated leading to severe amoebic dysentery
- Complications include intestinal perforation
- Trophozoites may spread to the liver, and other organs
- Rarely, abscesses spread to overlying skin
Difference between bacillary and amoebic dysentery?
Shigella sp. (bacillary) • Many PMN in stool • Eosinophilsabsent • Many bacilli in stool • Blood/mucus present in stool
Entamoeba (amoebic) • Few PMN in stool • Eosinophils present • Few amoebae in stool • Blood/mucus present in stool
Difference between the treatment of G. lamblia, C.parvum and E.histolytica?
G. lamblia
• Mepacrine hydrochloride
• Metronidazole
• Tinidazole
C.parvum
• Nitazoxanide
• Spiramycin
E.histolytica
• Metronidazole
ORT for all.
