6. Protozoal and Helminthic Infections of the Gastrointestinal Tract

Question 1

Name the protozoal infections of the large and small intestine

Answer 1

Small intestine:
Giardia lamblia
Cryptosporidium parvum

Large intestine:
Entamoeba histolytica

Question 2

Describe the features of giardia lamblia

Answer 2

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

Question 3

Describe the life cycle of giardia lamblia

Answer 3

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

Question 4

Describe the pathogenesis of giardia lamblia

Answer 4

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

Question 5

Describe the clinical manifestations of giardia lamblia

Answer 5

Mild infections are asymptomatic
Diarrhoea usually self limiting
Chronic diarrhoea presents in immunocompromised patients
Stools are characteristically loose, foul smelling and fatty

Question 6

Describe the features of cryptospordium parvum

Answer 6

Opportunistic infection
Transmission through faecally contaminated drinking water
Animal resevoir
Infective dose 10 oocysts

Question 7

Describe the life cycle of cryptospordium parvum

Answer 7

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

Question 8

Describe the pathogenesis of cryptospordium parvum

Answer 8

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

Question 9

Describe the clinical manifestations of cryptospordium parvum

Answer 9

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

Question 10

Describe the features of entamoeba histolytica

Answer 10

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

Question 11

Describe the pathogenesis of entamoeba histolytica

Answer 11

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

Question 12

Describe the clinical manifestations of entamoeba histolytica

Answer 12

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

Question 13

Compare bacillary vs amoebic dysentery

Answer 13

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

Question 14

How is giardia lamblia treated

Answer 14

Mepacrine hydrochloride
Metronidazole
Tinidazole

Question 15

How is cryptospordium parvum treated

Answer 15

Nitazoxanide

Spiramycin

Question 16

How is entamoeba histolytica treated

Answer 16

Metronidazole

Question 17

Name the Helminthic infections of the GI tract

Answer 17

Strongyloides stercoralis - pinworm/threadworm
Trichuris trichiura - whipworm
Ascaris lumbricoides - giant roundworm
Enterobius vermicularis - pinworm/threadworm
Ancylostoma duodenale - hookworm
Taenia solium - tapeworm

Question 18

Describe the features of strongyloides stercoralis

Answer 18

Pinworm
Disruption of small intestinal mucosa
Villous atrophy
Marked loss of elasticity of intsetinal wall

Question 19

Describe the clinical manifestations of strongyloides stercoralis

Answer 19

Dysentery
Dehydration
Malabsorption
Anal prurtis
Association with appendicitis

Question 20

Describe the features of trichuris trichiura

Answer 20

Whip worm
Can live >3yr in gut
Acquired through ingesting eggs on vegetables

Question 21

Describe the features of ascaris lumbricoides

Answer 21

Giant round worm
Large thick white form
Adults live for two years in gut

Question 22

Describe the clinical manifsetations of ascaris lumbricoides

Answer 22

Allergic reaction in sensitised people
Digestive upsets
Protein/energy malnutrition
Intestinal blockages
Worm may invade nose, mouth

Question 23

Describe the features of enterobius vermicularis

Answer 23

Thread wor,
Small cylindrical nematodes
Females migrate to anus at night to lay eggs

Question 24

Describe the clinical features of enterobius vermicularis

Answer 24

Intense itching
Secondary bacterial infection
Mild catarrhal inflammation
Diarrhoea
Slight eosinophilia

Question 25

Describe the features of ancylostoma duodenale

Answer 25

Hookworm
Often picked up walking barefoot in infected areas
Attaches to small intestine, suck blood and protein
Causes hypochromic anaemia
Blood loss

Question 26

Describe the features of taenia solium

Answer 26

Acquired from ingesting eggs or worms in undercooked prok
Reside in large intestine
Scolex - for attachment