Malaria Flashcards
(29 cards)
How long does it take for malaria parasite to transfer from person-mosquito-person?
approximately 2 weeks
What are the two main types of malaria parasite?
P. falciparium: Causes a lot of morbidity and mortality
P. vivax: Cause of severe illness. Has a dormant stage in the liver
Where in the world is P. falciparium a major problem?
Sub-sahara Africa and PNG
Where in the world is P. vivax a major problem?
90% in Asia and south central America
Not common in Africa due to mutations that make people resistant
Who is at high risk of complications from malaria infection?
Pregnant women: causes low birth weight in neonate (most severe indicator of health)
Children: impacts on education and development and compounds poverty
What are some obstacles that need to be overcome to combat malaria?
More effective control measures (so far only have bed- nets doused with insecticides)
No vaccine currently available
Insecticide and drug resistance increasing
Social, economic and political factors
Can malaria be passed between species?
NO. The only exception is P. knowlesi
Describe the life cycle of P. falciparum?
Infected female mosquito bites host > Enters hepatocytes > replicates in hepatocytes > burst hepatocytes > enter blood > Merozoite undergoes sexual reproduction > new female mosquito takes up parasite > matures in mosquito
How long does it take for the parasite to enter the liver?
1-2 hours
How long does it take for the parasite to burst the hepatocyte and enter the RBC stage?
7-10 days
Is the entire lifecycle of malaria symptomatic for the host?
NO. The liver stage is asymptomatic
What are the clinical features of uncomplicated malaria?
‘Flu-like’ - fever, headache, malaise
What are the clinical features of severe malaria?
Severe anaemia Cerebral complications (coma, convulsions, neuro deficits - 15-30% of children with this will die) Respiratory destress and metabolic acidosis (reduced tissue perfusion and lung damage.
What is the treatment for mild malaria?
3 day course of anti-malarial tablets (90% effective)
Aremisinin combination therapy
for P. vivax clearance of liver stage: primaquine
What is the treatment for severe malaria?
ASAP: anti-malarials IV artemisinin or quinine (7-10 days)
Supportive therapy: IV fluids, blood transfusion, anti-convulsives, anti-coagulants and anti-inflam drugs
Describe the illness associated with malaria?
Parasite accumulation in vital organs
Inflammatory response
Destruction of RBC from spleen (even uninfected cells)
Can immunity to malaria develop?
Eventually yes but the individual will have 20-30 episodes of infection
What are the types of immunity to malaria?
Immunity to prevent: severe malaria (specific antigens are recognised) OR any malaria (Ab targeting conserved epitopes or antibodies for all serotypes)
Immunity to malaria in pregnancy
Why is there slow development of immunity to malaria?
There is a lot of antigenic variation - polymorphic evades the immune system
Can switch on/off genes to evade responses
Host immune response may be inadequate, non-functional or develop poor memory
What are the important adaptive immune system responses to malaria?
B cells: Antibodies for neutralisation, opsinization (phagocytosis) ans complement binding (lysis)
T cells: CD4 and CD8 (and activated Macrophages
Can people become immune to malaria? If so, how?
YES.
Genetic factors: sickle cell trait, alpha thalassaemia or some particular blood groups can be resistant.
Innate immunity: Plasma type (complement, MBL), innate cell response (NK cell) and activated macrophage
Acquired immunity
How does acquired immunity to malaria work?
This can occur at different stages of infection in malaria life cycle.
- Sporozoite stage: Ab and Tcell response inhibit infection of hepatocytes
- Liver stage: T cell response CD8+ againstinfected hepatocytes
- Merozoite stage: Ab response
- Infected RBC: Ab and T cells. RBC lack MHC so CD8+ cells are of no use. CD4+ cells play a supportive role in splenic clearance (and macrophage phagocytosis) of infected RBC. Ab to merozoites inhibit invasion of RBC or Ab to proteins on RBC surface can cause opsinisation of RBC for phagocytosis (PROBLEM: lots of variation)
Why is it important to have a good understanding of how immunity develops
Vaccine development
Does the cell mediated immune response in the blood stage of malaria infection contribute to disease?
It depends on what cytokines are produced. IFN-gamma is associated with protection but the pro-inflammatory cytokines (TNF-a) are associated with severe disease
