Plasmodia

Question 1

What are the stages of a plasmodia infection?

Answer 1

Hepatic
Asexual Blood Stage
Vector Stage

Question 2

Describe what occurs in the hepatic stage.

Answer 2

Sporozoites from the mosquito vector enter the liver cells and become a hypnozoite which develops into a schizont. This releases buds of merozoites called a merozome. The merozoites infect RBCs.

Question 3

Describe the asexual blood stage

Answer 3

Merozoite becomes trophozoite which becomes schizont which may release more merosomes.

Question 4

What parasitic stage is taken up by the vector?

Answer 4

Gametes

Question 5

What happens in the vector?

Answer 5

Gametes form zygotes in the midgut. These become ookinetes which forms an oocyst containing sporozoites which are released into the mosquito salivary gland.

Question 6

Does sexual reproduction occur in the human?

Answer 6

Yes but only very small amounts

Question 7

What species does plasmodium infect?

Answer 7

A wide range. But there is rarely more than one host species infected by each species of Plasmodia

Question 8

Why is it different to determine virulence factors in plasmodial species?

Answer 8

Different hosts have different pathology.

Question 9

What is Ro?

Answer 9

A mathmatical model - basically a parasite needs to infect > or = to one host before it dies.

Question 10

What factors may affect transmission?

Answer 10

Climate - therefore vector density
Hypnozoite lifespan (very long lived)
Vector lifespan (1-2 weeks)
Host density
Migration of hosts

Question 11

What group is malaria particularly damaging to?

Answer 11

Children. Pregnant women (both of these have low immune status) Also soldiers.

Question 12

Is there a danger of malaria in britain?

Answer 12

Anopheles mosquito can transmit the disease

Some sporadic cases from imported mosquitoes.

Question 13

What is the effect of malaria on the human population as a whole?

Answer 13

Affects children, pregnant women and people from non-endemic areas the most.

It can alter the genetic makeup of a population (e.g. sickle-cell aneamia)

Question 14

What are the caveats to malarial immunity?

Answer 14

It is slow to develop and requires repeated exposures. It is also not very long lasting and is not a sterilising immunity. It is also area specific.

Anti-toxin immunity seems to be reached before anti-parasite immunity in children.

Question 15

How can the vector be controlled?

Answer 15

Biological control - fish
DDT - pressure for its use
Bed nets - controversy
Sleeping next to cows
insect repellants

Question 16

How do merozoites infect RBCs?

Answer 16

They have to recognise proteins on the blood cell surface.

Question 17

Do many sporozoites survive when injected into the host?

Answer 17

No - they must penetrate liver cells rapidly.

Question 18

Why would one not be able to vaccinate against P.falciparum and P. vivax with the same molecule?

Answer 18

They recognise different RBC proteins.

Question 19

Why do plasmodial infections often go unnoticed by the immune system?

Answer 19

AGs are only expressed by the RBCs when absolutely neccessary to the parasite. (last 12h of the LC)

Question 20

Why do people often become ill in 48h waves?

Answer 20

This is the time taken for the asexual blood stage to occur. Bursting of the blood cells is associated with toxin release.

Question 21

Why is important that gametes do not express antigens?

Answer 21

Most of them are not taken up by mosquitoes so any antigens that are expressed will stimulate immune responses.

Question 22

How is maturation of gametes induced in the mosquito?

Answer 22

changes in temperature and pH.

Question 23

Why are the sexual stages a good vaccination target?

Answer 23

They have very little antigenic variation.

Question 24

What are the problems with transmission blocking vaccines?

Answer 24

There is ethical problems as the person vaccinated sees no benefit to themselves but there is a risk of an adverse reaction to vaccination.