Parasitology: Helminths

Question 1

What are the main classifications of helminths?

Answer 1

1. Flatworms
   - trematodes (flukes)
   - cestodes (tapeworms)
2. Round worms
   - filarial (have juvenile offspring)
   - non-filarial

Question 2

What helminths are segmented?

Non-segmented?

Answer 2

Segmented: tapeworms (cestodes)

Non-Segmented: flukes (trematodes), nematodes

Question 3

What 2 types of life-cycle do helminths have?

Answer 3

1. direct (1 host)

2. indirect (>1 host)

Question 4

What is the definitive host?

Answer 4

The organism in which the sexually reproducing parasite reaches sexual maturity.

Question 5

What is the intermediate host?

Answer 5

The organism in which larval, juvenile or non-sexual stages develop.

Question 6

Describe the life cycle of Ascrais:

Answer 6

Helminth, fecal-oral, DIRECT

Question 7

What are the 6 ways in which helminths harm their hosts?

Answer 7

1. mechanical (obstruction/barrier)=Ascaris, Filaria
2. Compete with host for resources= Tapeworms (B12), Hookworm (iron)
3. Cytotoxicity= Flukes (liver fluke)
4. Inflammation= flukes (in blood; Schistosoma–> granuloma)
5. Immune-mediated injury = filaria
6. Malignant transformation = flukes

Question 8

What is the host response to helminths consistent of?

Answer 8

Cell-mediated immunity:

• effector cell activation w release of cytokines
• macrophages, PMNs, phagocytic cells, NK cells, CTL
• TH2 response necessary to clear intestinal worms (extracellular pathogen)
• eisonophils: degranulate onto IgE-coated worms

Question 9

What are the hallmarks of immune response to worm infx?

Answer 9

• eisonophilia

- high circulating IgE

Question 10

What cytokines to TH2 cells secrete to activate effector cells?

Answer 10

IL-4
IL-5
IL-13

Question 11

What are the 6 means of helminth diagnosis?

Answer 11

1. direct examination (stool helminths)
2. culture (strongyloides)
3. antigen detection (blood flukes, filaria)
4. host antibody detection (all tissue invasive worms)
5. nucleic acid amplification some tissue invasive worms)
6. radiologic (hydatid cyst, cysticerosis)

Question 12

What are the 2 medical Rx for helminths?

Answer 12

1. conventional anti-parasitics (all helminths)

2. herbs/plant extracts (pumpkin seeds for tapeworm)

Question 13

What are the 3 interventional Rx for helminths?

Answer 13

1. percutaneous drainage (hydatid cyst)
2. endoscopic removal (biliary ascaris, intraventricular neurocysticercosis)
3. surgical excision (hydatid cyst, filaria)

Question 14

What causes Neurocysticercosis?

What is its life cycle?

Answer 14

Taenia solium (larval stage of tapeworm in pork=cysticerci)

helminth, ingestion, indirect

Question 15

What antiparasitics are used to treat Cysticercosis?

What interventional treatment is used

Answer 15

• Albendazole
• Praziquantel

-Endoscopic removal (from ventricles)

Question 16

What is the life cycle of cutaneous larva mirgans?

Answer 16

-Helminth, Skin, penetration INDIRECT

Question 17

What is the treatment for cutaneous larva migrans?

Answer 17

• Albendazole

- Ivermectin

Question 18

What is the worm that crawls across the eyeball?

Answer 18

Loiasis

a type of filariasis, roundworm/nematode

Question 19

What is the life cycle of Loa loa?

Answer 19

Helminth, vector-borne, INDIRECT

Question 20

What condition is caused by Loaisis infection?

Answer 20

Elephantiasis due to lymphatic filariasis (mechanical obstruction of lymphatics)

Question 21

What treatments are used for Filariasis?

Answer 21

• ABs: Doxycycline
• Antiparasitic: Diethylcarbamazine, Albendazole, Ivermectin
• Interventional:
• surgical excision (from eye, nodulectomy)