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Medical Microbiology > GI Parasites > Flashcards

GI Parasites Flashcards

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Biology 101 flashcards USMLE® Step 1 flashcards
1
Q

Describe the features of a cestode

A
  • No mouth, digestive tract or vascular system
  • Scolex (a head but not a head)
  • Attaches to intestinal wall by suckers
  • Tegument (whole body)
    * Absorbs nutrients
  • Proglottids (segments)
    * Form the tegument
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2
Q

How is Taenia Saginata transmitted?

A

Cyst in beef

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3
Q

What are the symptoms of infection by Taenia Saginata?

A

Epigastric pain
Vomiting
Diarrhoea

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4
Q

How is Tania Solium transmitted?

A

Cyst in pork

Faecal-oral (causes cysticercosis)

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5
Q

What are the symptoms of infection by Tania Solium?

A

Epigastric pain
Vomiting
Diarrhoea

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6
Q

What are the symptoms of Cysticercosis?

A

Muscle pain and weakness, ocular and neurologic problems

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7
Q

Describe the features of proglottids

A

Each tapeworm is made up of many proglottids in a ‘tape’

  • Contains male and female reproductive organs producing large quantities of infective eggs
    * Eggs are infectious
    * Proglottids break off - These are infectious too
  • Hermaphrodite
    * Self fertilise (sperm & egg from same proglottid)
    * Cross fertilise (sperm & egg from different proglottid)
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8
Q

Describe the lifecycle of the tapeworm

A

Eggs or gravid proglottids in faeces and passed into environment

Cattle and pigs become infected by ingesting vegetation infected by eggs or gravid proglottids

Oncospheres hatch, penetrate intestinal wall and circulate into musculature

Oncospheres develop into cysticerci in muscle

Humans infected by eating raw or undercooked infected meat

Scolex attaches to intestine

Adults in small intestine

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9
Q

When does cysticercosis occur?

A

Only occurs when humans eat infected Taenia eggs from pig

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10
Q

Where is cysticercosis most common?

A

– China
– India
– Central & South America
– West / Central / Southern Africa

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11
Q

Describe the pathogenesis of cysticercosis

A

• Occurs when humans consume pork tape worm eggs (not undercooked meat)
– This is what usually happens in pigs
– Poor sanitation
– Faecally contaminated food/water

• The eggs hatch in the intestine
– But instead of developing into an adult
– Penetrate the mucosa
– Migrate to muscles / brain / eyes – Develop into cysticerci

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12
Q

How is Taenia infection diagnosed?

A

Fresh faecal sample (eggs & proglottids)
• Looking for the presence of eggs

Biopsy of the infected tissue or X-Ray
• Presence of calcified larvae in tissue

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13
Q

How is Taenia infection treated?

A
  • Praziquantal

* Albendazole + steroids (cysticercosis)

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14
Q

How is Taenia infection prevented?

A 
Cook pork properly (T. solium)
Cook beef properly (T. saginata)
Keep pigs away from human areas, prevents:
• Poor hygiene
• Contamination of water supplies
• Contamination of crops
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15
Q

Give examples of pathogenic amoebae

A

Naegleria fowleri
Acanthamoeba spp.
Balamuthia mandrillaris
Entamoeba histolytica

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16
Q

What disease does Naegleria fowleri cause?

A

• Primary amoebic meningoencephalitis (PAM)

17
Q

What diseases does Acanthamoeba spp. cause?

A
  • Granulomatous amoebic encephalitis (GAE)

* Acanthamoeba keratitis (AK)

18
Q

What disease does Balamuthia mandrillaris cause?

A

• Balamuthia amoebic encephalitis (BAE)

19
Q

What diseases does Entamoeba histolytica cause?

A
  • Amoebic dysentery

* Amoebiasis

20
Q

Describe the epidemiology of Entamoeba histolytica

A

10% of world population are infected
• 50% in some areas
100,000 deaths per annum
• Invasive infection

• More prevalent in tropical and developing countries, due to:
• Poor sanitation
• Use of human faeces to fertilise/irrigate crops
- Night Soil

21
Q

Describe the features of Entamoeba histolytica

A

Enteric pathogen

• Transmitted by the faecal-oral route by contaminated food or water

22
Q

What are the symptoms of infection by Entamoeba histolytica?

A 
Asymptomatic or abdominal pain/cramps
Rectal prolapse
• Trophozoites penetrate the intestinal mucosa
Dysentery
• Bloody watery faeces
Trophozoites full of erythrocytes can be seen in samples
Hepatic abscess – Invasive infection
Necrosis of the liver
Other sites (Lungs / Brain) - Rare
23
Q

Describe the pathogenesis of entamoeba histolytica infection

A

Amoebae attach to a galactose lectin on intestinal epithelium

This causes the release of cysteine proteases
• Digests cell
• Forms Amoebapore

Entry of parasite into epithelium causes an immune response
• Release of cytokines (IL-8)
• Neutrophil and Eosinophil influx

D – Invades the body
• Inflammation helps the entry
• Can migrate to liver to form an abscess
• Inflammatory damage / tissue lysis

24
Q

How is Entamoeba histolytica infection diagnosed?

A
  • Microscopic examination of faeces for cysts
  • Aspirate abscess
  • Serology (IFA) - antibodies
25
Q

How can Entamoeba histolytica infection be prevented?

A

• Avoid contaminated foods
• Wash fruit / veg before eating
• Drink bottled / chemically treated water
- Iodine (Chlorine / Silver not effective)

26
Q

How is Entamoeba histolytica infection treated?

A 
Metronidazole / Tinidazole
• Taken up by diffusion
• Prodrug
• Targets pyruvate:ferredoxin oxidoreductase system in the mitochondria of obligate anaerobes
• Knocks out anaerobic respiration
27
Q

What problems occur with metronidazole treatment

A

Aldehyde-dehydrogenase inhibitor

• Disulfiram reaction - You cannot drink alcohol

28
Q

Are there any commensal amoeba found in the gut?

A

Entamoeba coli & Entamoeba dispar

29
Q

Describe the features of Giardiasis

A 
Non fatal infection
• Often associated with hikers and drinking lake/river water
Caused by Giardia lamblia
 Intestinal flagellate
• Uses its flagella to swim
30
Q

Describe the life cycle of Giardia

A

Two stage life cycle
• Cyst
• Trophozoite

Patient ingests cysts from contaminated food or water

Excystation occurs after it passes through the stomach

Trophozoites feed and divide in the intestine

Encystation occurs when trophozoites pass into lower part of the intestine

Cysts are passed in faeces

31
Q

What are the symptoms of Giardiasis?

A
  • Diarrhoea
  • Bloating
  • Steatorrhea (smelly, pale, greasy, floaters)
32
Q

What complications can occur with Giardiasis?

A 
Can cause villous atrophy
• Problem in developing countries
• Poor diet
• Malabsorption syndrome
• Malnutrition
33
Q

Describe the pathology of Giardiasis

A

Production of cathepsin protease
• Damages villi

Lysis of villi
• Damages villi and tight cellular junctions
• Bacterial translocation

Immune response
• Inflammation in intestinal wall
• T cell proliferation
• Neutrophil chemotaxis
• Further damage to villi
34
Q

How is Giardiasis diagnosed?

A
  • Microscopy of faeces (IFA)

* Culture of duodenal aspirate

35
Q

How is Giardiasis treated?

A

Metronidazole or Tinidazole

36
Q

How is Giardiasis prevented?

A
  • Avoid contaminated foods and water
  • Drink bottles water
  • Use purification tablets

Medical Microbiology (13 decks)

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