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)
Why are nematode infections the most important intestinal worms ?
Because they are the most common
How are nematode infections transmitted ? How are nematode infections diagnosed ?
TRANSMISSION
-Often soil-transmitted
-Infection occurs either by:
• swallowing infective eggs (Ascaris lumbricoides, Trichuris trichiura)
• active skin penetration by larvae and systemic migration through lung to intestine (Strongyloides stercoralis)
DIAGNOSIS
-Diagnosis by stool microscopy
S. STERCORALIS
- Type of worm
- Pathogenesis
S. STERCORALIS -Type of worm: Pinworm -Pathogenesis: • Disruption of small intestinal mucosa • Villous atrophy • Marked loss of elasticity of intestinal wall
What are the clinical manifestations of S. STERCORALIS infection ?
- Dysentery (persistent in immunocompromised hosts)
- Dehydration
- Malabsorption syndrome
- Anal pruritis
- Association with appendicitis
Main problem: one helminthic infection that can complete its whole life cycle in human host (replication does occur)
T. TRICHURIA
- Type of worm
- Transmission
T. TRICHURIA
- Type of worm: Whipworm
- Transmission: Acquired through ingesting eggs on vegetables
How many years can T. Trichuria live in the gut ? How many eggs does it produce daily ?
- Can live for 3 years in gut
* 10,000 eggs produced daily
A. LUMBRICOIDES
-Type of worm
A. LUMBRICOIDES
-Type of worm: Giant roundworm (large thick white worm 20-30 cm)
How many years can A. lumbricoides live in the gut ? How many eggs do female A. lumbricoides produce per day (from 65 days after infection) ?
- Adults live in gut for 2 years
* Females produce approx. 20,000 eggs / day from 65 days after infection
What are the clinical manifestations of A. lumbricoides infection ?
- Allergic reaction in sensitised people
- Digestive upsets
- Protein/energy malnutrition
- Intestinal blockages
- Worm may invade mouth nose etc.
ENTEROBIUS VERMICULARIS
- Type of worm
- Pathogenesis
- Clinical manifestations
ENTEROBIUS VERMICULARIS
- Type of worm: Threadworm (small cylindrical nematodes < 1 cm)
- Pathogenesis: female migrates to anus at night to lay approx. 10,000 eggs, which may develop to infective stage within hours
- Clinical manifestations: Intense itching, secondary bacterial infection – mild catarrhal inflammation and diarrhoea, slight eosinophilia
ANCYLOSTOMA DUODENALE
- Type of worm
- Transmission
- Pathogenesis
- Clinical manifestations
ANCYLOSTOMA DUODENALE
- Type of worm: Hookworm
- Transmission: Often picked up walking barefoot in infected areas
- Pathogenesis: Attaches to small intestine, suck blood and protein, often present in huge numbers
- Clinical manifestations: Cause hypochromic anaemia
How much blood loss does ANCYLOSTOMA DUODENALE cause ?
Blood loss 0.03ml/day/worm (often 500-1000 worms)
TAENIA SOLIUM
- Type of worm
- Transmission
TAENIA SOLIUM
- Type of worm: Tapeworm
- Transmission: Acquired from ingesting worms or eggs in undercooked pork
- Pathogenesis: Reside in large intestine (uses scolex for attachment), can grow up to 7m long
Describe prevention for intestinal helminth infections.
Improved hygiene and sanitation (including hand washing, and good cooking of food) are important in prevention of infection
Identify the main problems posed for Antiprotozoal and Antihelminthic Agents.
- Large variety of species
- Complexities of their life cycles
- Differences in their metabolic pathways
- Drugs active against protozoa are inactive against helminths
