PaBi (11): vaccines for human nematodes

Question 1

What is the difference between monovalent and multivalent vaccines?

Answer 1

Monovalent vaccinates against one strain or organism or only contains one antigen where as multivalent vaccinates against multiple

Question 2

What type of vaccine are nematode vaccines?

Answer 2

monovalent

Question 3

What is the effect of hookworms and other soil transmitted nematodes on quality of life?

Answer 3

They cause morbidity rather than mortality. Affect the number of “useful” healthy days you have in your life. Many children can’t go to school and this means they have a 40% reduction in their ability to earn money so continues the cycle of poverty

Question 4

What is the most prevalent of hookworms?

Answer 4

Necator americanus

Question 5

What is the lifecycle of the hookworm?

Answer 5

Live for 1-2 years in the small intestine, females produce ~10,000 eggs per day which are excreted into the environment. The eggs hatch and the larva molts 3 times and burrow into the skin. They travel through the lymphatics to the lungs, up the trachea and are swallowed so they reach the small intestine.

Question 6

What are the pathological effects of helminth infections?

Answer 6

They drink a lot of blood (~1ml per day) so can lead to severe anaemia.

Question 7

What are the problems of using drug based control for hookworms?

Answer 7

Frequent use leads to resistance and the effects of the drug don’t last very well so people are easily reinfected if there is high numbers of the worm

Question 8

What was the ideal hookworm vaccine?

Answer 8

Vaccinate against multiple antigens and life stages, and provide protection into adulthood

Question 9

What were the realistic aims of creating the vaccine, since sterilising immunity was not an option?

Answer 9

To reduce the severity of the infection and reduce blood and nutrient loss

Question 10

What hookworm stage is the dog vaccine against?

Answer 10

The third larvae stage, L3

Question 11

What antigen is a potential vaccine candidate in humans?

Answer 11

Activation-associated secretory proteins (ASP-2) secreted from the L3

Question 12

Why was the vaccine with ASP-2 halted?

Answer 12

In phase 1 clinical trial some people had type 1 hypersensitivity reactions so now adult worm antigens are being researched.

Question 13

What is a promising vaccine target in the adult worm?

Answer 13

Glutathione-S-transferase which converts toxic haem into a non-toxic substance so blocking this would kill the parasite