Protozoal and Helminthic Infections of the Gastrointestinal Tract Flashcards
How do transmissions of intestinal protozoa and helminths occur ?
- Transmission of intestinal protozoa and helminths depends on contact with faecal-derived material.
- Usually acquired through ingestion of contaminated food or water
How do protozoal/helminthic infections usually present (in terms of symptoms) ?
Symptoms of protozoal/helminthic infections usually present as acute to chronic diarrhea and inflammation
Which kinds of places are protozoal/helminthic infections prevalent in ?
Places where hygiene/sanitation standards are poor
To what extent are protozoal/helminthic infections local in the body ?
Protozoal/helminthic infections may spread from one part of the GI to another GI organ
Identify the main protozoa associated with GI infections, and state where each one acts.
SMALL INTESTINE:
- Giardia lamblia
- Cryptospridium parvum
LARGE INTESTINE:
-Entamoeba histolytica
G. LAMBLIA
- Disease caused
- Transmission
- Infective dose
- Diagnosis
G. LAMBLIA
- Disease caused: Giardiasis (frequent cause of travellers’ diarrhea)
- Transmission: in drinking and recreational water, but can also be passed on person to person
- Infective dose: 10-25 cysts
- Diagnosis: microscopy of stool samples
Describe the life cycle of G. lamblia.
2 stages:
1) Trophozoite (when causing damage to microvili)
- Flagellated and bi-nucleated
- Liver in upper part of small intestine
- Adheres to brush border of epithelial cells (using sucker)
2) Cyst
- Forms when trophozoites form resistant wall
- Passes out in stools
- Can survive for several weeks
Describe the pathogenesis of G. lamblia.
- Present in the duodenum, jejunum and upper ileum
- Attaches to mucosa via central sucker
- Does NOT penetrate the surface
- Causes damage to mucosa, and villous atrophy
- Leads to malabsorption of foods, especially fats and fat soluble vitamins
- May swim up the bile duct to the gall bladder
What are the clinical manifestations of G. lamblia infection ?
G. lamblia infections:
- Mild infections are asymptomatic
- Diarrhea usually self-limiting (7-10 days)
- Chronic diarrhea occurs in immunocompromised patients
- Stools characteristically loose, foul smelling, and fatty
CRYPTOSPORIDIUM PARVUM
- Transmission
- Human only ? Animal reservoir ?
- Infection dose
- Other
CRYPTOSPORIDIUM PARVUM
- Transmission: drinking faecally-contaminated water
- Animal reservoir (cattle)
- Infection dose: as few as 10 oocysts
- Other: opportunistic infection (AIDs defining condition)
Describe the life cycle of Cryptosporidium parvum.
- Sexual and asexual development within the host
- Ingestion of resistant oocysts
- Release of infective sporozoites within small intestine
- Invasion of intestinal epithelium
- Division to form merozoites which re-infect cells
- After sexual phase, oocysts released (in feces)
Describe the pathogenesis of Cryptosporidium parvum.
- Enters cells of the microvillus border of small intestine
- Remains within vacuole of epithelial cell
- May multiply to give large numbers of progeny, especially in immunocompromised hosts
What are the clinical manifestations of Cryptosporidium 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
- Disease caused
- Where found ?
- Transmission
E. histolytica
- Disease caused: Amoebic Colitis (which may show deep ulcers)
- Where found ? Common in tropical and sub-tropical countries: prevalent in >50% of population
- Transmission: via ingestion of contaminated food or water, also through anal sexual activity
Describe the 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
Describe the life cycle of E. histolytica.
- 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 red blood cells giving rise to amoebic colitis
- Trophozoite stages live in large intestine and pass out as resistant, infective cysts
Describe the main clinical manifestations of E. histolytica.
- Small localised superficial ulcers leading to mild diarrhea
- Entire colonic mucosa may become deeply ulcerated leading to severe amebic dysentry
- Complications include intestinal perforation
- Trophozoites may also spread to liver and other organs
- RARELY, abscesses spread to overlying skin
Distinguish between bacillary and amoebic dysentry.
1) BACILLARY DYSENTRY
-Shigella spp
• Many PMN in stool
• Eosinophilsabsent
• Many bacilli in stool
• Blood/mucus present in stool
2) AMOEBIC DYSENTRY
-Entamoeba histolytica
• Few PMN in stool
• Eosinophilspresent
• Few amoebae in stool
• Blood/mucus present in stool
Describe the treatment for G.lamblia protozoal infections.
- Mepacrinehydrochloride
- Metronidazole
- Tinidazole
+ORT
Describe the treatment for C.parvum protozoal infections.
- Nitazoxanide
- Spiramycin
+ORT
Describe the treatment for E.histolytica protozoal infections.
• Metronidazole
+ORT
How may we prevent protozoal infections of the GI tract ?
- Improved hygiene and water supplies
- Eating only freshly prepared food served hot
- Avoiding salads and fruit which cannot be peeled
- Avoiding tap water and ice cubes
Identify the main types and subtypes of helminths.
1) Roundworms (Nematodes)
– Bisexual
– Cylindrical
2) Tapeworms (Cestodes)
– Elongated flatworms
– Segmented
– Hermaphrodite
3) Flukes (Trematodes)
– Leaf-shaped flatworms
– Mainly hermaphrodites
– Rare in humans
Identify the main helminths which cause GI infections.
Roundworms (Nematodes):
• Strongyloides stercoralis (pinworm / threadworm)
• Trichuris trichiura (whipworm)
• Ascaris lumbricoides (giant roundworm)
• Enterobius vermicularis (pinworm / threadworm)
• Ancylostoma duodenale (hookworm)
Tapeworms (Cestodes):
• Taenia solium (tapeworm)
