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MD3002 > Protozoal and Helminthic Infections of the Gastrointestinal Tract > Flashcards

Protozoal and Helminthic Infections of the Gastrointestinal Tract Flashcards

1
Q

How do transmissions of intestinal protozoa and helminths occur ?

A
  • Transmission of intestinal protozoa and helminths depends on contact with faecal-derived material.
  • Usually acquired through ingestion of contaminated food or water
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2
Q

How do protozoal/helminthic infections usually present (in terms of symptoms) ?

A

Symptoms of protozoal/helminthic infections usually present as acute to chronic diarrhea and inflammation

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3
Q

Which kinds of places are protozoal/helminthic infections prevalent in ?

A

Places where hygiene/sanitation standards are poor

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4
Q

To what extent are protozoal/helminthic infections local in the body ?

A

Protozoal/helminthic infections may spread from one part of the GI to another GI organ

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5
Q

Identify the main protozoa associated with GI infections, and state where each one acts.

A

SMALL INTESTINE:

  • Giardia lamblia
  • Cryptospridium parvum

LARGE INTESTINE:
-Entamoeba histolytica

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6
Q

G. LAMBLIA

  • Disease caused
  • Transmission
  • Infective dose
  • Diagnosis
A

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
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7
Q

Describe the life cycle of G. lamblia.

A

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

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8
Q

Describe the pathogenesis of G. lamblia.

A
  • 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
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9
Q

What are the clinical manifestations of G. lamblia infection ?

A

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
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10
Q

CRYPTOSPORIDIUM PARVUM

  • Transmission
  • Human only ? Animal reservoir ?
  • Infection dose
  • Other
A

CRYPTOSPORIDIUM PARVUM

  • Transmission: drinking faecally-contaminated water
  • Animal reservoir (cattle)
  • Infection dose: as few as 10 oocysts
  • Other: opportunistic infection (AIDs defining condition)
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11
Q

Describe the life cycle of Cryptosporidium parvum.

A
  • 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)
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12
Q

Describe the pathogenesis of Cryptosporidium parvum.

A
  • 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
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13
Q

What are the clinical manifestations of Cryptosporidium parvum ?

A
  • 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
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14
Q

E. histolytica

  • Disease caused
  • Where found ?
  • Transmission
A

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
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15
Q

Describe the pathogenesis of E. histolytica.

A

• 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

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16
Q

Describe the life cycle of E. histolytica.

A
  • 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
17
Q

Describe the main clinical manifestations of E. histolytica.

A
  • 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
18
Q

Distinguish between bacillary and amoebic dysentry.

A

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

19
Q

Describe the treatment for G.lamblia protozoal infections.

A
  • Mepacrinehydrochloride
  • Metronidazole
  • Tinidazole

+ORT

20
Q

Describe the treatment for C.parvum protozoal infections.

A
  • Nitazoxanide
  • Spiramycin

+ORT

21
Q

Describe the treatment for E.histolytica protozoal infections.

A

• Metronidazole

+ORT

22
Q

How may we prevent protozoal infections of the GI tract ?

A
  • 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
23
Q

Identify the main types and subtypes of helminths.

A

1) Roundworms (Nematodes)
– Bisexual
– Cylindrical

2) Tapeworms (Cestodes)
– Elongated flatworms
– Segmented
– Hermaphrodite

3) Flukes (Trematodes)
– Leaf-shaped flatworms
– Mainly hermaphrodites
– Rare in humans

24
Q

Identify the main helminths which cause GI infections.

A

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)

25
Q

Why are nematode infections the most important intestinal worms ?

A

Because they are the most common

26
Q

How are nematode infections transmitted ? How are nematode infections diagnosed ?

A

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

27
Q

S. STERCORALIS

  • Type of worm
  • Pathogenesis
A 
S. STERCORALIS
-Type of worm: Pinworm
-Pathogenesis: 
• Disruption of small intestinal mucosa
• Villous atrophy
• Marked loss of elasticity of intestinal wall
28
Q

What are the clinical manifestations of S. STERCORALIS infection ?

A
  • 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)

29
Q

T. TRICHURIA

  • Type of worm
  • Transmission
A

T. TRICHURIA

  • Type of worm: Whipworm
  • Transmission: Acquired through ingesting eggs on vegetables
30
Q

How many years can T. Trichuria live in the gut ? How many eggs does it produce daily ?

A
  • Can live for 3 years in gut

* 10,000 eggs produced daily

31
Q

A. LUMBRICOIDES

-Type of worm

A

A. LUMBRICOIDES

-Type of worm: Giant roundworm (large thick white worm 20-30 cm)

32
Q

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) ?

A
  • Adults live in gut for 2 years

* Females produce approx. 20,000 eggs / day from 65 days after infection

33
Q

What are the clinical manifestations of A. lumbricoides infection ?

A
  • Allergic reaction in sensitised people
  • Digestive upsets
  • Protein/energy malnutrition
  • Intestinal blockages
  • Worm may invade mouth nose etc.
34
Q

ENTEROBIUS VERMICULARIS

  • Type of worm
  • Pathogenesis
  • Clinical manifestations
A

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
35
Q

ANCYLOSTOMA DUODENALE

  • Type of worm
  • Transmission
  • Pathogenesis
  • Clinical manifestations
A

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
36
Q

How much blood loss does ANCYLOSTOMA DUODENALE cause ?

A

Blood loss 0.03ml/day/worm (often 500-1000 worms)

37
Q

TAENIA SOLIUM

  • Type of worm
  • Transmission
A

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
38
Q

Describe prevention for intestinal helminth infections.

A

Improved hygiene and sanitation (including hand washing, and good cooking of food) are important in prevention of infection

39
Q

Identify the main problems posed for Antiprotozoal and Antihelminthic Agents.

A
  • Large variety of species
  • Complexities of their life cycles
  • Differences in their metabolic pathways
  • Drugs active against protozoa are inactive against helminths

MD3002 (95 decks)

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