Plasmodium

Plasmodium/ Malaria
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Plasmodium
Disease Malaria is caused by four plasmodia:
- Plasmodium Falciparum ( most common causes of malaria)
- Plasmodium vivax
- Plasmodium ovale
- Plasmodium malariae
Important properties
? The vector and definitive host is the female Anopheles mosquito.
? There are two phases in the life cycle: the sexual cycle (in mosquitoes) & the asexual cycle (in humans, the intermediate hosts).
? The sexual cycle is called sporogony (sporozoites are produced). & the asexual cycle is called schizogony (schizonts are made).
Pathogenesis &Epidemiology
? Destruction of red blood cells by release of merozoites& the action of the spleen to first sequester the infected red cells & then to lyse them.
? The enlarged spleen is due to congestion of sinusoids with erythrocytes, coupled with hyperplasia of lymphocytes & macrophages.
? Malaria caused by P. falciparum is more severe than that caused by other plasmodia:
1. It is characterized by infection of far more red cells than the other species & by occlusion of the capillaries with aggregates of parasitized red cells. This is lead to hemorrhage and necrosis particularly in the brain (cerebral malaria).
2. P. falciparum is chloroquine resistance. These strains now predominate in most areas of the world where malaria is endemic. This resistance is mediated by a mutation in the gene encoding the chloroquine transporter in the cell membrane of the organism.
3. P. falciparum causes a high level of parasitemia, because it can infect red cells of all ages.
? Extensive hemolysis and kidney damage occur, with resulting hemoglobinuria. The dark color of the patient’s urine has given rise to the term (black water fever). The hemoglobinuria can lead to acute renal failure.
? The timing of the fever cycle is 72 h. for P. malariae & 48 h. for the other plasmodia
Plasmodium/ Malaria
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? Disease caused by P. malariae is called quartan malaria because it recurs every fourth day, whereas malaria caused by the others is called tertian malaria because it recurs every third day.
? Tertian malaria is subdivided into malignant malaria, caused by P. falciparum, & benign malaria, caused by P. vivax &P. ovale.
? Malaria is transmitted by mosquito bites, but transmission across the placenta, in blood transfusions, and by intravenous drug abuse also occurs.
? More than 200 million people worldwide have malaria and more than 1 million die of it each year, making it the most common lethal infectious disease.
Plasmodium/ Malaria
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Clinical findings
? Fever (The fever spike reach 41c , accompanied by Shaking chills). Fever followed by drenching sweats
? Headache
? Myalgias & Arthralgias
? Nausea & Vomiting
? Abdominal pain
? Splenomegaly & hepatomegaly
? Anemia
? Malaria caused by P. falciparum is life-threatining, Malaria caused by the other plasmodia is self-limited.
? Relapses of P. vivax &P. ovale malaria occur up to several years after the initial illness as a result of hypnozoites latent in the liver.
Lab. Diagnosis
? Microscopic examination of blood, by thick and thin Giemsa-stained smears.
Thick smear to screen for the presence of organisms & thin smear for species identification.
? PCR-based test for Plasmodium nucleic acids or an ELISA test for a protein specific for P. falciparum.
Treatment
? Chloroquine for acute malaria ,chloroquine kills the merozoites, butdose not affect the hypnozoites, these are killed by Primaquine .
? For chloroquine-resistant strains of P. falciparum either Mefloquine or combination of quinine & doxycycline is used. Also a combination of atovaquone &proguanil.
? In sever cases intravenous administration of either quinidine (or quinine) plus another drug such as doxycycline or clindamycin should be used.
? The artemisinins, such as artesunate or artemether, are used in combination with other antimalarial drugs.
Plasmodium/ Malaria
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Prevention
? Chemoprophylaxis for travelers to areas where chloroquine-resistant P. falciparum is endemic consists of mefloquine or doxycycline.
? A combination of atovaquone and proguanil also be used.
? Travelers to areas where the other three plasmodia are found should take chloroquine 2 weeks before arrival & 6 weeks after departure, followed by 2 week course of primaquine.
? Mosquito netting, window screens, protective clothing and insect repellents.
? Many insecticide sprays such as DDT.
? There is no vaccine
Reference:-
? Medical Microbiology & Immunology. Levinson, et al . (2008).