Vl 11 Nematodes II

Question 1

Which parasitic disease is close to extinction? Explain.

Answer 1

Guineaworm infection

through the eradication program:
human is the primary host⇒ can be controlled by identifying all cases and modifying human behavior to prevent it from recurring (assuring access to clean drinking water, detecting + containing infected people and keeping them away from water)

Once all human cases are eliminated, the disease cycle will be broken, resulting in its eradication

Question 2

Which parasitic diseases can lead to anemia? Why?

Answer 2

• malaria (from Plasmodium) invades erythrocytes and let’s them rupture after proliferating
• hookworms = blood feeding nematodes ⇒ attach to mucosa and constantly bite

Question 3

Describe the life cycle of Onchocerca volvulus

Answer 3

1) blackfly bite transmits L3
2) mature into adults in subcutaneous knot
3) adults produce microfilariae (found in skin and lymphatics of connective tissues)
5) filariae taken up by Blackfly
6) penetrate midgut and migrate to thoracic muscle
7) develop to L3, migrate to head and proboscis

Question 4

Describe the life cycle of Wucheria bancrofti.

Answer 4

1) mosquito injects L3 larvae into skin
2) develop to adults (reside in lymphatics)
3) produce microfilariae (migrate into lymph and blood channels)
4) filariae ingested by mosquito⇒ penetrate mosquitos midgut and migrate to thoracic muscles
6) develop to L3 larvae
7) migrate to head and proboscis

Question 5

What factors determine the disease spectrum in patients with Onchocerca volvulus infections?

Answer 5

• number of filariae in host
• immune response against microfilariae
• if tending towards inflammation or not
• susceptibility of patient to immune modulation of parasite:
  ~30% hyperreactive: strong pathology with inflammation around mostly dead filariae
  ~30% hyporeactive: cellular suppressed with swollen lymph nodes, produce microfilariae
  ~30% silent resistant: no filariae

Question 6

How does mebendazole, the major anti-helminthic drug, act?

Answer 6

selectively inhibits synthesis of microtubules ⇒ destroys extant cytoplasmic microtubules in parasite intestinal cells⇒ blocks uptake of glucose and other nutrients⇒ gradual immobilization and eventual death of the helminths

Question 7

What are strategies for hookworm vaccines? What are alternative control measures?

Answer 7

• vaccine with irradiated L3 larvae to generate immune response
• combination of two antigens:
• ASP-2 and APR-1 to reduce larval migration through tissue (ASP-2) and block hemoglobinases (APR-1)

also:

• wear proper shoes or sandals
• sanitary institutions

Question 8

What are control strategies against Onchocerca volvulus?

Answer 8

• spraying insecticides at vector breeding sites (fast flowing rivers)
• kill microfiliariae with Ivermectin (annually)
• nodulectomy (removal of knots caused by onchocerca)
• antibiotic treatment vs wolbachia endosymbiont in Onchocerca (doxycycline)
• exposure to cattle filaria O. ochengi (not developing in humans) provides partial immunity