GI Parasites Flashcards
Describe the features of a cestode
- 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
How is Taenia Saginata transmitted?
Cyst in beef
What are the symptoms of infection by Taenia Saginata?
Epigastric pain
Vomiting
Diarrhoea
How is Tania Solium transmitted?
Cyst in pork
Faecal-oral (causes cysticercosis)
What are the symptoms of infection by Tania Solium?
Epigastric pain
Vomiting
Diarrhoea
What are the symptoms of Cysticercosis?
Muscle pain and weakness, ocular and neurologic problems
Describe the features of proglottids
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)
Describe the lifecycle of the tapeworm
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
When does cysticercosis occur?
Only occurs when humans eat infected Taenia eggs from pig
Where is cysticercosis most common?
– China
– India
– Central & South America
– West / Central / Southern Africa
Describe the pathogenesis of cysticercosis
• 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
How is Taenia infection diagnosed?
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
How is Taenia infection treated?
- Praziquantal
* Albendazole + steroids (cysticercosis)
How is Taenia infection prevented?
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
Give examples of pathogenic amoebae
Naegleria fowleri
Acanthamoeba spp.
Balamuthia mandrillaris
Entamoeba histolytica
What disease does Naegleria fowleri cause?
• Primary amoebic meningoencephalitis (PAM)
What diseases does Acanthamoeba spp. cause?
- Granulomatous amoebic encephalitis (GAE)
* Acanthamoeba keratitis (AK)
What disease does Balamuthia mandrillaris cause?
• Balamuthia amoebic encephalitis (BAE)
What diseases does Entamoeba histolytica cause?
- Amoebic dysentery
* Amoebiasis
Describe the epidemiology of Entamoeba histolytica
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
Describe the features of Entamoeba histolytica
Enteric pathogen
• Transmitted by the faecal-oral route by contaminated food or water
What are the symptoms of infection by Entamoeba histolytica?
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
Describe the pathogenesis of entamoeba histolytica infection
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
How is Entamoeba histolytica infection diagnosed?
- Microscopic examination of faeces for cysts
- Aspirate abscess
- Serology (IFA) - antibodies
How can Entamoeba histolytica infection be prevented?
• Avoid contaminated foods
• Wash fruit / veg before eating
• Drink bottled / chemically treated water
- Iodine (Chlorine / Silver not effective)
How is Entamoeba histolytica infection treated?
Metronidazole / Tinidazole • Taken up by diffusion • Prodrug • Targets pyruvate:ferredoxin oxidoreductase system in the mitochondria of obligate anaerobes • Knocks out anaerobic respiration
What problems occur with metronidazole treatment
Aldehyde-dehydrogenase inhibitor
• Disulfiram reaction - You cannot drink alcohol
Are there any commensal amoeba found in the gut?
Entamoeba coli & Entamoeba dispar
Describe the features of Giardiasis
Non fatal infection • Often associated with hikers and drinking lake/river water Caused by Giardia lamblia Intestinal flagellate • Uses its flagella to swim
Describe the life cycle of Giardia
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
What are the symptoms of Giardiasis?
- Diarrhoea
- Bloating
- Steatorrhea (smelly, pale, greasy, floaters)
What complications can occur with Giardiasis?
Can cause villous atrophy • Problem in developing countries • Poor diet • Malabsorption syndrome • Malnutrition
Describe the pathology of Giardiasis
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
How is Giardiasis diagnosed?
- Microscopy of faeces (IFA)
* Culture of duodenal aspirate
How is Giardiasis treated?
Metronidazole or Tinidazole
How is Giardiasis prevented?
- Avoid contaminated foods and water
- Drink bottles water
- Use purification tablets
