Plasmodia Flashcards
What are the stages of a plasmodia infection?
Hepatic
Asexual Blood Stage
Vector Stage
Describe what occurs in the hepatic stage.
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.
Describe the asexual blood stage
Merozoite becomes trophozoite which becomes schizont which may release more merosomes.
What parasitic stage is taken up by the vector?
Gametes
What happens in the vector?
Gametes form zygotes in the midgut. These become ookinetes which forms an oocyst containing sporozoites which are released into the mosquito salivary gland.
Does sexual reproduction occur in the human?
Yes but only very small amounts
What species does plasmodium infect?
A wide range. But there is rarely more than one host species infected by each species of Plasmodia
Why is it different to determine virulence factors in plasmodial species?
Different hosts have different pathology.
What is Ro?
A mathmatical model - basically a parasite needs to infect > or = to one host before it dies.
What factors may affect transmission?
Climate - therefore vector density Hypnozoite lifespan (very long lived) Vector lifespan (1-2 weeks) Host density Migration of hosts
What group is malaria particularly damaging to?
Children. Pregnant women (both of these have low immune status) Also soldiers.
Is there a danger of malaria in britain?
Anopheles mosquito can transmit the disease
Some sporadic cases from imported mosquitoes.
What is the effect of malaria on the human population as a whole?
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)
What are the caveats to malarial immunity?
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.
How can the vector be controlled?
Biological control - fish DDT - pressure for its use Bed nets - controversy Sleeping next to cows insect repellants
How do merozoites infect RBCs?
They have to recognise proteins on the blood cell surface.
Do many sporozoites survive when injected into the host?
No - they must penetrate liver cells rapidly.
Why would one not be able to vaccinate against P.falciparum and P. vivax with the same molecule?
They recognise different RBC proteins.
Why do plasmodial infections often go unnoticed by the immune system?
AGs are only expressed by the RBCs when absolutely neccessary to the parasite. (last 12h of the LC)
Why do people often become ill in 48h waves?
This is the time taken for the asexual blood stage to occur. Bursting of the blood cells is associated with toxin release.
Why is important that gametes do not express antigens?
Most of them are not taken up by mosquitoes so any antigens that are expressed will stimulate immune responses.
How is maturation of gametes induced in the mosquito?
changes in temperature and pH.
Why are the sexual stages a good vaccination target?
They have very little antigenic variation.
What are the problems with transmission blocking vaccines?
There is ethical problems as the person vaccinated sees no benefit to themselves but there is a risk of an adverse reaction to vaccination.
