Malaria

Question 1

What is the genus of protozoans that cause malaria? What are the species?

Answer 1

Plasmodium

P. malariae

P. falciparum

P. ovale

P. vivax

all of these species can cause it

Question 2

What species of mosquito carries these parasites?

Answer 2

The Anopheles mosquito, the FEMALE Anopheles mosquito

Question 3

What is the phylum which contains these protozoans?

What are some of their defining characteristics?

Answer 3

Sporozoa, previously called Apicomplexa.

Obligate intracellular parasites.

Spore-forming (sporozoites).

Non-motile, with no structures for movement? Slide said this, but plasmodium sporozoites are definitely motile.

Complex, multiple life stages.

Question 4

How is Malaria diagnosed? Which species causes malaria?

Answer 4

By blood smear and Giemsa stain

Or by PCR of blood sample

Question 5

Describe the life cycle

Answer 5

Injection of motile, spindle-shaped sporozoiteswhen the mosquito bites. This initiates theAsexualportion of their life cycle,called schizogony.

Sporozoites infect liver cells where they develop into Schizonts (dividing by nuclear multiplication hundreds of times, then forming individual cell membranes around them)

Liver cells rupture, merozoites are released into the blood and infect RBCs.

Merozoites or immature trophozoites, the ball shaped form which looks like signet rings develop inside of the RBCs. A Trophozoite undergoes thousands of nuclear divisions inside the RBC. Then membranes form around these nuclei, and they are called merozoites.

RBCs rupture,starting the exo-erythrocyte cycle, andmerozoites re-infect more RBCs, starting the erythrocyte cycle again.

Some merozoites form Gametocytes, which die if they aren’t eaten by a mosquito within a few days.

In the mosquito they can go through the Sporogonic Cycle, forming megagametocytes and microgametocytes and reproducing sexually.

In P. vivax and P. ovale a dormant stage [hypnozoites] can persist in the liver and cause relapses by invading the bloodstream weeks, or even years later

Question 6

What are the species that cause malaria and the differences between them

Answer 6

P. falciparum: The most common and most deadly species. RBC bursts and fever at irregular intervals every 36-48 hours.

P. vivax and P. ovale: Both can form dormant stage in the liver and cause relapses after months or years. RBC bursts are every 48 hours regularly, called tertian malaria.

P. malariae: RBC bursts every 72 hours, called quartan malaria.

Question 7

Clinical presentation of malaria

Answer 7

Periodic episodes of severe fever and chills

Last about 6 hours and correspond to cycles of RBC ruptures.

RBC invasion causes anemia and sticky/viscous RBCs

Hepatosplenomegaly occurs as the reticuloendothelial (macrophage) system clears the lysed RBCs and debris

RBCs plug vessels, causing diffuse haemorrhage and ischemia

• renal failure
• pulmonary edema
• coma
• seizures
• death

Death rates are highest in sub-saharan children who develop cerebral malaria

Question 8

What are some genetic factors that are protective against malaria?

Answer 8

Sickle cell anemia is protective against P. falciparum

People who lack the Duffy a & b antigens on their RBCs are protected against P. vivax

Question 9

How is malaria diagnosed?

Answer 9

RBC smears

History and geography

Immunohistochemistry of the blood smear to identify species

PCR of blood sample.

Question 10

Malaria treatment and prevention

Answer 10

Chlorquine, a specific drug for malaria, which inhibits the parasites ability to de-toxify metabolites from heme degradation.

Chloroquine resistant strains exist: use mefloquine, quinine, and artemisin

To treat P. vivax and P. ovale, Primaquine must be used to eliminate potential hypnozoite spores dormant in the liver.

Prevention:

• mosquito nets
• pesticides and repellents for Anopheles mosquito,
• Chloroquine, or mefloquine and doxycycline prophylaxis