Infection 2: Pathogenesis of malaria Flashcards
Why is the cases of malaria decreasing in malaria endemic areas? (2)
ITNs Indoor residual spraying Diagnostics Treatment Prevention in pregnancy
What types of fever do the fevers cause
p. falciparum: malignatnt tertian
p. vivax: benign tertian
p. ovale: tertian
p. malariae: quartan
p. knowlesi: quotidian
Describe the life cycle of plasmodium
look at diagram
Name 3 methods for diagnosis of malaria (3)
giemsa stained blood film
Rapid diagnostic test
thick and thin film
what does microscopy tell you about malaria?
Species (may be multiple)
Parasitemia (density)
Parasite stage
how does malaria RDT work?
antibody is bound on the RDT and and the blood sample is then put onto test and the antibody will bind to the antigen from the blood and the fluorescent marker on the antibody will be positive.
Name 3 issues with RDTs
They are less sensitive by 10 – 100x than microscopy
Detect parasite antigen rather than live parasite
may therefore be positive in patients who have been recently treated (up to 2 weeks) or come from a malaria endemic area and have a low level of asymptomatic parasitaemia
Not possible to determine the % parasitaemia or stage of parasite
How is malaria classified?
UNCOMPLICATED
Parasitaemia <2% AND no schizonts AND no clinical complications
SEVERE Parasitaemia >2% or Parasitaemia <2% plus… either schizonts reported on blood film or complications
How does malaria infect RBCs and evade the immune system? (3)
The parasite regularly exchanges the expressed var gene, leading to antigenic variation. As an antibody response forms to 1 PfEMP, there is a switch of expression to alternative PfEMPs, escaping the immune response and maintaining infection.
On the surface of the Infected Red Blood Cell, the parasite expresses an adhesive molecule called Plasmodium falciparum Erythrocyte Membrane Protein, PfEMP-1
features of severe malaria
cerebral anaemia, anaemia, jaundice, resp distress, renal impairment, blackwater fever, hypoglycaemia
what score is used in children for cerebral malaria
Unrousable COMA in the presence of peripheral parasitaemia
where other causes of ENCEPHALOPATHY have been excluded
In children the Blantyre coma score is used. (Total score of 3 or less -> CM)
The clinician must be alert to ANY alteration in consciousness
Diffuse cerebral dysfunctions. Generalised convulsions
Focal neurologic signs and brainstem signs (abnormal oculo-vestibular reflexes)
Abnormalities of posture and muscle tone
Differential Diagnosis: Meningitis (including TB), encephalitis, brain access….
Describe the pathogenesis of malarial anaemia (3)
[1] Haemolysis of iRBC
[2] Haemolysis of uRBC
[3] Bone Marrow Suppression (dyserythropoiesis)
mx of malaria?
IV artesunate and may add primiquinine
action of artesunate
stops at ring stage
Artesunate kills circulating ring-stage parasites as well as schizonts whereas quinine does not. Both artesunate and quinine are active against the more pathological cytoadhering stages that sequester in the venules and capillaries of vital organs. Thus, artesunate prevents maturation of the younger parasite stages and thereby prevents sequestration,34 which reduces consequent microcirculatory obstruction
how is sickle cell protective ?
Sickle cell trait – HbS relatively protected
Because P. falciparum malaria has been a leading cause of death in Africa since remote times, the sickle cell trait is now more frequently found in Africa and in persons of African ancestry than in other population groups.
