Protozoal and Helminth Infections of the GI tract Flashcards
What do rates of intestinal protozoa and helminth infections in a population generally reflect?
Hygiene / sanitation standards
How are new infections brought about?
- Contact with faecal-derived material
- Usually acquired through ingestion of contaminated food or water
What do infections generally present with?
Acute to chronic diarrhoea and inflammation
What bacterial disease can lie dormant in the gallbladder?
Salmonella
What protozoal infections affect the SI?
- Giardia lamblia
- Cryptosporidium parvum
What protozoal infections affect the LI?
- Entamoeba histolytica
What protozoal infection is a frequent cause of travellers’ diarrhoea?
Giardia Lamblia
What are the 2 stages of giardia lamblia life cycle?
Trophozoite - Flagellated and bi-nucleated - Lives in upper part of SI - Adheres to brush border of epithelial cells Cyst - Formed when trophozoite forms 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 the mucosa via ventral sucker
- Does not penetrate surface
- Causes damage to the mucosa and villous atrophy
- Leads to malabsorption of food, esp. fats and fat soluble vitamins
- May swim up the bile duct to gall bladder
What are the clinical manifestations of G. lamlia infection?
- MIld infections are asymptomatic
- Diarrhoea is usually self-limiting (7-10 days)
- Chronic diarrhoea presents in immunocompromised patients
- Stools are characteristically foul-smelling and fatty
What led to a massive increase in cryptosporidium parvum infections in the past?
AIDS epidemic (oppurtunistic infection)
How is C. parvum transmitted and what is the reservoir?
- Usually through faecally-contaminated drinking water
- Animal reservoir (usually cattle)
- As few as 10 oocysts required for infection
Describe the life cycle of C. parvum
- Host ingests oocysts with sporozoites
- Sporozoites attach to host cells and invade intestinal epithelium
- Division to form merozoites which re-infect cells can cause auto-infection
- Sexual phase and produce fertilized oocysts
- Mature oocyst then released in faeces
What are the 2 different types of C. parvum cysts?
- Thin walled stay in host
- Thick walled are released into environment
Describe the pathogenesis of C. parvum
- Enters cells of the microvillus border of SI
- Remains within vacuole of epithelial cell
- May multiply to give large numbers of prgeny, especially in immunocompromised hosts
How much faeces can be produced as a result of C. parvum infection?
25 litres of watery faeces / day
What does Entamoeba histolytica cause?
Emebic dysentary
How can E. histolytica be transmitted?
- Contaminated food or water
- Anal sexual activity
What can amoebic ulcers cause?
After mucosal invasion, cysts invade RBCs giving rise to amoebic colitis
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 toxin to the host
What are the clinical manifestation of E. hostolytica?
- Small localised superficial ulcers leading to mild diarrohoea
- Entire colonic mucosa may become deeply ulcerated leading to severe amoebic dysentery
- Complications include intestinal perfusion
- Trophozoites may spread to the liver, and other organs
- Rarely, abscesses spread to overlying skin
What are the differences between bacillary and amoebic dysentery?
- Bacillary have many PMN in stool few in entamoeba
- Eosinophils abscent in bacillary present in amoebic
- Many bacilli in stool few amoebae in stool
- Blood/mucus in both
What antibiotic is very affective against protozoal infection?
Metronidazole
What are the ingrediants in ORS?
- Glucose 13.6g/L
- NaCl 2.6g/L
- KCl 1.5g/L
- Trisodium citrate dihydrate 2.9g/L
What are the features of roundworms (nematodes)?
- Bisexual
- Cylindrical
What are the features of tapeworms (Cestodes)?
- Elongated flatworms
- Segmented
- Hermaphrodite
What are the features of flukes (Trematodes)?
- Leaf-shaped flatworms
- Mainly hermaphrodites
- Rare in humans
Name some helminthic organisms which infect the GI tract
- Strongyloides stercoralis (pinworm / threadworm)
- Trichuris trichiura (whipworm)
- Ascaris lumbricoides (giant roundworm)
- Enterobius vermicularis (pinworm / threadworm)
- Ancylostoma duodenale (hookworm)
- Taenia solium (tapeworm)
What are the most clinically relevant intestinal worms?
Nematodes
How are nematodes often transmitted?
- Often soil-trnsmitted
- Swallowing infective eggs
- Active skin penetration by larvae and systemic migration through lung to intestine (strongyloides stercoralis)
How are nematode infections diagnosed?
Stool microscopy
What are the features of Strongyloides stercoralis?
- Pinworm
- Cresnt shaped
How does S. stercoralis affect the GI tract?
- Disrupts small intestinal mucosa
- Villous atrophy
- Marked loss of elasticity of intestinal wall
What are the clinical manifestations of S. stercoralis?
- Dysentery (persistent in immunocompromised hosts)
- Dehydration
- Malabsorption syndrome
- Anal pruritis
- Association with appendictis
How long can Trichuris trichiura live in the gut for?
Over 3 years
What does T. trichiura look like?
Whipworm
How is T. trichiura transmitted?
Acquired through eggs on vegetables
What is the appearence of Ascaris lumbricoides?
- Giant roundworm
- Large thick white worm approx. 20 - 30 cm
How many eggs to A. lumbricoides produce?
approx 20,000 eggs / day from 65 days after infection
How long does A. lumbricoides live in the gut for?
Adult lives in gut for 2 years
How prevelant is A. lumbricoides infection?
- 1 million clinical cases per year
- 20,000 deaths
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.
What does Enterobius vermicularis look like?
- Threadworm
- Small cylindrical nematodes < 1 cm
How does E. vermicularis infect humans?
- Female migrates to anus at night to lay approx. 10,000 eggs, which may develop to infective stage within hours
What is the clinical manifestation of E. vermicularis infection?
- Intense itching
- Secondary bacterial infection
- Mild catarrhal inflammation and diarrhoea
- Slight eosinophilia
What does ancylostoma duodenale look like?
Hookworm
How can ancyclostoma duodenale be transmitted?
Walking barefoot in infected areas
What are the affects of A. duodenale / what does it do?
- Attaches to SI, suck blood and protein, often present in huge numbers
- Cause hypochromic anaemia
- Blood loss 0.03ml/day/worm (often 500-1000 worms)
What kind of worm is Taenia solium?
Tapeworm
How large can Taenia solium grow?
7m
Where does Taenia solium reside?
The large intestine
How is T. solium usually transmitted?
Ingesting worms or eggs in undercooked pork
What part of T. solium attaches to the intestine?
Scolex
What are the diffficulties around antiprotozoal and antihelminthic agents?
- Large variety of species to treat
- Complexities of their life cycles
- Differences in their metabolic pathways
- Drugs active against protozoa are inactive against helminths
