6. Protozoal and Helminthic Infections of the Gastrointestinal Tract Flashcards
Name the protozoal infections of the large and small intestine
Small intestine:
Giardia lamblia
Cryptosporidium parvum
Large intestine:
Entamoeba histolytica
Describe the features of giardia lamblia
Frequent cause of travellers diarrhoea Detected in drinking and recreational water Can be passed person-person Infective dose 10-25 cysts Diagnosis by microscopy of stool samples
Describe the life cycle of giardia lamblia
Trophozite:
Flagellated and binucleated
Lives in upper part of small intestine
Adheres to brush border of epithelial cells
Cyst:
Formed when trophozite forms resistant wall
Passes out in stools
Can survive for several weeks
Describe the pathogenesis of giardia lamblia
Present in duodenum, jejunum and upper ileum
Attaches to mucosa via ventral sucker
Does not penetrate the surface
Causes damage to mucosa and villous atrophy
Leads to malabsorption of food; esp. fats and fat soluble vitamins
May swim up the bile duct to gall bladder
Describe the clinical manifestations of giardia lamblia
Mild infections are asymptomatic
Diarrhoea usually self limiting
Chronic diarrhoea presents in immunocompromised patients
Stools are characteristically loose, foul smelling and fatty
Describe the features of cryptospordium parvum
Opportunistic infection
Transmission through faecally contaminated drinking water
Animal resevoir
Infective dose 10 oocysts
Describe the life cycle of cryptospordium parvum
Asexual and sexual development within host
Ingestion of resistant oocysts
Release of infective sporozoites in small intestine
Invasion of intestinal epithelim
Division to form merozoites which re-infect cells
After sexual phase, oocytes released
Describe the pathogenesis of cryptospordium parvum
Enters cells of microvillus border of small intestine
Remains within vacuole of epithelial cell
May multiply to give large numbers of progeny, especially in immunocompromised hosts
Describe the clinical manifestations of cryptospordium parvum
Moderate to severe diahhroea
Up to 25L/day
In HIV + people with CD4+ T-cell counts of <100/mm3, diahhroea is prolonged and may become irreversible
Describe the features of entamoeba histolytica
Trasnmission via ingestion of contaminated food and water; also anal sexual activity
Cysts pass through stomach and excyst in the small intestine giving rise to progeny
These adhere to epithelial cells and cause damage mainly through cytolysis
After mucosal invasion, cysts invade RBCs giving rise to amoebic colitis
Trophozite stage live in large intestine and passed out as resistant, infective cysts
Describe the pathogenesis of entamoeba 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 which are toxic to the host
Describe the clinical manifestations of entamoeba 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
Trophozites may spread to liver and other organs
Rarely, abscesses spread to overlying skin
Compare bacillary vs amoebic dysentery
Shigella sp.: Many PMN in stool Eosinophils absent Many bacilli in stool Blood/mucus present in stool
Entamoeba: Few PMN in stool Eosinophils present Few amoebae in stool Blood/mucus present in stool
How is giardia lamblia treated
Mepacrine hydrochloride
Metronidazole
Tinidazole
How is cryptospordium parvum treated
Nitazoxanide
Spiramycin
How is entamoeba histolytica treated
Metronidazole
Name the Helminthic infections of the GI tract
Strongyloides stercoralis - pinworm/threadworm
Trichuris trichiura - whipworm
Ascaris lumbricoides - giant roundworm
Enterobius vermicularis - pinworm/threadworm
Ancylostoma duodenale - hookworm
Taenia solium - tapeworm
Describe the features of strongyloides stercoralis
Pinworm
Disruption of small intestinal mucosa
Villous atrophy
Marked loss of elasticity of intsetinal wall
Describe the clinical manifestations of strongyloides stercoralis
Dysentery Dehydration Malabsorption Anal prurtis Association with appendicitis
Describe the features of trichuris trichiura
Whip worm
Can live >3yr in gut
Acquired through ingesting eggs on vegetables
Describe the features of ascaris lumbricoides
Giant round worm
Large thick white form
Adults live for two years in gut
Describe the clinical manifsetations of ascaris lumbricoides
Allergic reaction in sensitised people Digestive upsets Protein/energy malnutrition Intestinal blockages Worm may invade nose, mouth
Describe the features of enterobius vermicularis
Thread wor,
Small cylindrical nematodes
Females migrate to anus at night to lay eggs
Describe the clinical features of enterobius vermicularis
Intense itching Secondary bacterial infection Mild catarrhal inflammation Diarrhoea Slight eosinophilia
Describe the features of ancylostoma duodenale
Hookworm
Often picked up walking barefoot in infected areas
Attaches to small intestine, suck blood and protein
Causes hypochromic anaemia
Blood loss
Describe the features of taenia solium
Acquired from ingesting eggs or worms in undercooked prok
Reside in large intestine
Scolex - for attachment
