Malaria Flashcards
What’s the life cycle of malaria?
Replicats in gut of mosquito then it’s present in the saliva which when it bites a human enters their tissue
Invades liver cell, does asexual replication there, then hepatocyte ruptures & releases the progeny into the blood
In the blood it infects erythrocytes –> ring form –> trophozoite
Erythrocyte ruptures –> releases the merozoites which invade new erythrocytes
What’s responsible for the pathology of malaria?
Due to the asexual erythrocytic stage parasites
Bursing releases parasite material and metabolites which causes an immune response
What is the progression of illness in malaria?
Incubation period between time of inoculation and appearance of symptoms
Prodromal nonspecific flu-like symptoms
Febrile attacks with perodicities
These start with a cold stage (shivering, 1 hour), then hot stage (heat, dry burning skin, headache), sweating stage (2-4 hours, fever declines),
Then fall asleep
What are the different periodicities for teh different types of malaria?
P. ovale and P. vivax = 48 hours
P. falciparum = 48 hours but is more irregular
P. malariae = 72 hours
What’s the most severe form of malaria? Most benign? Why?
P. falciparum = most severe, bc large number of merozoites & ability to invade all stages of erythrocytes
The other species are rarely lethal
P. ovale = most benign
P. malariae = benign but chronic
P. vivax and ovale prefer immature erythrocytes
Why is P. vivax rarely found in west africa?
Duffy receptor on erythrocytes is required to get pathogenesis; this is not found in people in the population of west africa
Where is are the diff strains of malaria found?
P. ovale: Subsaharan Africa, Western Pacific Islands
P. vivax: SE Asia, Americas
P. falciparum: Subsaharan africa
P. malariae: follows P. falciparum
Which strains have the lowest parasitemia?
P. ovale and P. vivax: both are difficult to distinguish, because of this & because RBC not as enlarged
P. malariae: low load causes chronic stage & does not have a persistent liver stage (perhaps spleen?)
Which strains have a dormant strain? What is the significance of this?
P. vivax and P. ovale
Means that you have to treat accordingly: not sensitive to chloroquine, quinine, mefloquine, artemisinin
What’s the name of the plasmodium stage that invades the liver? Blood cells?
Sporozoite: hepatocytes
Merozoite: erythrocytes
Why can P. falciparum lead to cerebral malaria? What is cerebral malaria?
Cerebral malaria = impaired consciousness, convulsions, headache, ultimately coma
2 hypotheses: (1) sequestration of infected erythrocytes in cerebral microvasculature (2) cytokine hypothesis - TNF-alpha –> NO –> affects neuronal function
Sequestration = due to “knobs” on infected erythrocyte making it more sticky and bind to endothelium/stay in organs; this protects the parasite from elimination from the bloodstream via the spleen
***unique to falciparum!!!
PfEMP1 is believed to be the protein on P. falciparum that is expored to erythrocyte surface & binds host receptors – note that one is beleived to be chondroitin sulfate A, which is present on placenta, so when a woman is pregnant, she can get sick even though she’s been immune her whole life
What is immunity to malaria like?
Develps by 5 years of age, not protective during pregnancy, short-lived so if you move away from an endemic area and come back you are no longer protected
Controls symptoms, not parasitemia!
People lacking Duffy antigen are refractory to P. vivax
Inherited erythrocyte disorders might protect against malaria (thalassemia, glucose-6-phosphate dehydrogenase deficiency)
How do you diagnose malaria?
How do you distinguish strains?
Recent exposure to endemic area
Interval to develpment of symptoms:
<10 days = P. falciparum
10-60 days: any species
>60 days: very unusual for P. falciparum
>3 years: P. malariae
Severity of illness: severe disease = P. falciparum
Flu-like symptoms +/- splenomegaly/hepatomegaly/anemia
Thick and thin smear
Rapid dipstick tests
On a smear, what does P. falciparum look like?
RBC is not enlarged, coarse dots, RBC might be distorted, pinkish/bluish color & darkened rim, 2 ring trophs
On a smear, what does P. vivax look like?
Very enlarged, stippling, one ring troph
Chart of “microscopic clues” for malaria on smear
Summary of comparison of the malaria subtypes
