GI Parasites

Question 1

Describe the features of a cestode

Answer 1

• 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

Question 2

How is Taenia Saginata transmitted?

Answer 2

Cyst in beef

Question 3

What are the symptoms of infection by Taenia Saginata?

Answer 3

Epigastric pain
Vomiting
Diarrhoea

Question 4

How is Tania Solium transmitted?

Answer 4

Cyst in pork

Faecal-oral (causes cysticercosis)

Question 5

What are the symptoms of infection by Tania Solium?

Answer 5

Epigastric pain
Vomiting
Diarrhoea

Question 6

What are the symptoms of Cysticercosis?

Answer 6

Muscle pain and weakness, ocular and neurologic problems

Question 7

Describe the features of proglottids

Answer 7

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)

Question 8

Describe the lifecycle of the tapeworm

Answer 8

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

Question 9

When does cysticercosis occur?

Answer 9

Only occurs when humans eat infected Taenia eggs from pig

Question 10

Where is cysticercosis most common?

Answer 10

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

Question 11

Describe the pathogenesis of cysticercosis

Answer 11

• 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

Question 12

How is Taenia infection diagnosed?

Answer 12

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

Question 13

How is Taenia infection treated?

Answer 13

• Praziquantal

* Albendazole + steroids (cysticercosis)

Question 14

How is Taenia infection prevented?

Answer 14

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

Question 15

Give examples of pathogenic amoebae

Answer 15

Naegleria fowleri
Acanthamoeba spp.
Balamuthia mandrillaris
Entamoeba histolytica

Question 16

What disease does Naegleria fowleri cause?

Answer 16

• Primary amoebic meningoencephalitis (PAM)

Question 17

What diseases does Acanthamoeba spp. cause?

Answer 17

• Granulomatous amoebic encephalitis (GAE)

* Acanthamoeba keratitis (AK)

Question 18

What disease does Balamuthia mandrillaris cause?

Answer 18

• Balamuthia amoebic encephalitis (BAE)

Question 19

What diseases does Entamoeba histolytica cause?

Answer 19

• Amoebic dysentery

* Amoebiasis

Question 20

Describe the epidemiology of Entamoeba histolytica

Answer 20

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

Question 21

Describe the features of Entamoeba histolytica

Answer 21

Enteric pathogen

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

Question 22

What are the symptoms of infection by Entamoeba histolytica?

Answer 22

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

Question 23

Describe the pathogenesis of entamoeba histolytica infection

Answer 23

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

Question 24

How is Entamoeba histolytica infection diagnosed?

Answer 24

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

Question 25

How can Entamoeba histolytica infection be prevented?

Answer 25

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

Question 26

How is Entamoeba histolytica infection treated?

Answer 26

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

Question 27

What problems occur with metronidazole treatment

Answer 27

Aldehyde-dehydrogenase inhibitor | • Disulfiram reaction - You cannot drink alcohol

Question 28

Are there any commensal amoeba found in the gut?

Answer 28

Entamoeba coli & Entamoeba dispar

Question 29

Describe the features of Giardiasis

Answer 29

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

Question 30

Describe the life cycle of Giardia

Answer 30

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

Question 31

What are the symptoms of Giardiasis?

Answer 31

* Diarrhoea * Bloating * Steatorrhea (smelly, pale, greasy, floaters)

Question 32

What complications can occur with Giardiasis?

Answer 32

``` Can cause villous atrophy • Problem in developing countries • Poor diet • Malabsorption syndrome • Malnutrition ```

Question 33

Describe the pathology of Giardiasis

Answer 33

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 ```

Question 34

How is Giardiasis diagnosed?

Answer 34

* Microscopy of faeces (IFA) | * Culture of duodenal aspirate

Question 35

How is Giardiasis treated?

Answer 35

Metronidazole or Tinidazole

Question 36

How is Giardiasis prevented?

Answer 36

* Avoid contaminated foods and water * Drink bottles water * Use purification tablets