Anti-Protozoals and Anti-Helminthics

Question 1

List the protozoal infections of the GI tract

Answer 1

Small intestine:

• giardia lambila
• cryptospordium parvum

Large intestine:
- entamoeba histolytica

Question 2

Describe the life cycle of G. lamblia and how it causes disease

Answer 2

2 stages of life cycle:
Trophozoite:
- flagellated and binucleated
- lives in upper part of small intestines
- adheres to brush border of epithelial cells (how it causes disease)

Cyst:

• formed when it forms resistant wall
• passes out in stools
• can survive for several weeks outside of host

Question 3

How would you treat G.lamblia?

Answer 3

intestinal trophozoite is treated with metronidazole or tinidazole in a single dose

Question 4

Describe the life cycle of C. parvum

Answer 4

• asexual and sexual development within host
• host ingests resistant oocysts
• release of infective sporozoites in small intestine
• invasion of intestinal epithelium
• divides to form merozoites that re-infect cells
• after sexual phase, oocytes are released

Question 5

What is the treatment for C. parvum?

Answer 5

proposed:

• paromomycin
• nitazoxanide
• spiramycin

Question 6

Describe the life cycle of E. histolytica

Answer 6

• cysts pass through stomach and excyst in small intestine to give rise to progeny
• these adhere to epithelial cells and cause damage through cytolysis
• after mucosal invasion cysts invasde RBCs to give rise to amoebic colitis
• trophozoite stages live in large intestines and pass out resistant infective cysts

Question 7

How do you treat amoebiasis?

Answer 7

• intestinal infection: metronidazole
• if chronic infection, cysts will survive and cause relapse that is resistant to metronidazole
• so treated with diloxanide furoate
• if abscess then treat with metronidazole at higher and longer doses

Question 8

How does metronidazole work?

Answer 8

• under aerobic conditions can generate toxic radicals that damage bacterial and protozoal DNA
• penetrates well in tissue
• used for E. histolytica and G. lambila

Question 9

What are the side effects of metronidazole?

Answer 9

• metallic taste

- acute nauseous reaction to alcohol

Question 10

What does diloxanide furoate do?

Answer 10

its an aminoglycoside that kills cystic amoebas but does not eradicate them from the gut

Question 11

What are the side effects of diloxanide furoate?

Answer 11

• flatulence
• itchiness
• hives

Question 12

What does paromomycin do?

Answer 12

its an aminoglycoside that kills cystic amoebas. Not absorbed by GI tract

Question 13

What are the side effects of paromomycin?

Answer 13

• abdo cramps
• diarrhoea
• heartburn
• nausea
• vomiting

Question 14

How can you prevent protozoal infections of GIT?

Answer 14

• improve hygiene and water supplies
• eat only freshly prepared food served hot
• avoid salads and fruit that cannot be peeled
• avoid tap water and ice cubes

Question 15

What are the different classes of helminths?

Answer 15

• nematodes (round worms)
• crestodes (flat worms)
• trematodes (flukes - leaf shaped)

Question 16

What are the pathological mechanisms of helminthic infections and its treatment?

Answer 16

• inflammation: anti-inflammatory drugs
• competition for nutrients: reduce worm burden and support nutrition
• space occupying lesions: helminth eradication and treatment of secondary effects
• stimulation of fibrosis: helminth eradication and treatment of secondary effects

Question 17

What are the intestinal helminths (of nematode class) and their pathological mechanism?

Answer 17

• ascaris (competition for nutrients, space occupying lesions)
• hookworm (competition for nutrients)
• enterobius (inflammation)
• trichiuris (competition for nutrients)

Question 18

What are the clinical features of trichiuris?

Answer 18

• whipworm that causes vague abdo symptoms
• trichiuris dysentery syndrome
• growth retardation
• intellectual compromise (due to micronutrient deficiency and mucosal integrity)

Question 19

What is the clinical manifestation of E. vermicularis?

Answer 19

• threadworm that causes intense itching
• secondary bacterial infection
• mild catarrhal inflammation
• diarrhoea
• slight eosinophilia

Question 20

What are the drugs used to treat intestinal helminths?

Answer 20

• praziquantel
• albendazole
• piperazine
• pyrantel
• levamisole
• ivermectin
• niclosamide

Question 21

How does praziquantel work?

Answer 21

• increases calcium permeability of membranes depolarising them (may interfere with purine synthesis)
• cestodes

Question 22

What are the side effects of praziquantel?

Answer 22

• dizziness
• headache
• drowsiness
• abdo cramps and nausea
• rash
• interacts with rifampicin, carbamazine, phenytoin

Question 23

How does albendazole work?

Answer 23

• for nematodes, some protozoa and some cestode
• binds to colchicine sensitive receptor or tubulin to prevent polymerisation into tubules
• impaires glucose uptake and depletes glycogen stores

Question 24

What are the side effects of albendazole?

Answer 24

• may be teratogenic
• persistent sore throat
• headaches
• dizziness
• acute liver failure
• aplastic anaemia and marrow suppression