Malaria

Study guide:

Definitions:  

​Malaria is a protozoan parasite widespread in the tropical and subtropical areas. It can be caused by four species of the genus Plasmodium, P. falciparum, P. Vivax, P. ovale, P. malariae, leading to acute or chronic infections. 

 

Epidemiology:

​-    Malaria is still a major health problem, each year 500 million people are affected, with 0.2% mortality rate. 
-     According to estimates from the World Health Organization, over 200 million cases and about 655.000 deaths have occurred in 2010.  
-    The parasite is bounded by geographical ranges because of its temperature-dependent cycle so it is mainly found in the tropics and subtropics.  
 

 

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  • In Saudi Arabia, Malaria is mainly found in the Jazan and Assir, in 2016, there were 272 reported indigenous confirmed cases.

Parasitology:

  • Malaria is transmitted by the bite of female anopheles mosquitoes which feed on blood meals. When the mosquito takes a meal containing gametocyte, the sexual form of the parasite, it becomes infected.

  • The developmental cycle inside the mosquito usually takes from 7-20 days to form the infective stage, sporozoites, which migrate to the salivary glands of the mosquito.

  • The mosquito will go for another meal and inoculate the sporozoites into the human host blood stream.

  • Some will be destroyed by the immune system while others will be taken by the liver, in which they multiply inside the hepatocytes as merozoites, this stage is called sporogony.

  • After few days, the hepatocytes rupture releasing the merozoites into circulation while others remain dormant in the hepatocyte (in case of P.ovale and P.vivax).

  • The released merozoites are taken by the erythrocytes to start the schizogony. Inside the erythrocytes the parasite starts multiplying, changing from merozoites to trophozoites then schizont and finally merozoites again.

  • Some trophozoites are changed into gametocyte rather than trophozoites, thus causing the infection when picked up by another mosquito.

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Pathogenesis:

The pathology of malaria is related to several causes:

  • Rupture of RBCs causing anemia.

  • Releasing pyrogens or cytokines causing fever.

  • Adhesion of red RBCs to the endothelium of small blood vessels in case of P.falciparum, causing vascular occlusion and severe organ damage.

  • P. ovale and P.vivax remain latent in the liver causing relapses.

  • Hypoglycemia because of parasitic consumption of glucose.

Clinical features:

Malaria has an incubation period of 10-21 days, yet it can be longer, during which there are no apparent symptoms. The main manifested symptom after the incubation period is fever; it also may be present with other symptoms like;

  • General malaise.

  • Headache, vomiting and diarrhea.

  • Tachycardia and rigors.

  • Profuse sweating.

  • Anemia.

  • Hepatosplenomegaly.

  • Cerebral malaria: where the patient loses consciousness, gets confused and convulsions and often progress to coma and death. (severe P. falciparum)

  • Blackwater fever: due to wide spread intravascular hemolysis affecting the RBCs and giving it black color. (severe P. falciparum)

-P. vivax and P. ovale infection: Relatively mild illness, and anemia develops slowly. Spontaneous recovery happens within 2-6 weeks. However, it has higher tendency to relapse.

-P. malariae: It also has a relatively mild illness, but it has a chronic course rather than acute. Parasitemia may endure for years with or without symptoms. In children, it may be associated with nephrotic syndrome and glomerulonephritis.

-P. falciparum: In many cases, it is considered as self-limiting disease with less marked paroxysmal fever, yet sometimes serious complications may develop. Majority of malaria deaths are due to P. falciparum serious complications. parasitemia levels >1% of infected cells  is an indicator of severe falciparum malaria.

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Diagnosis:

Malaria should be suspected in anyone who has been in malaria endemic areas, regardless of the period after the exposure.

  • The gold standard diagnosis tool is thick and thin films identifying malaria parasite (Thick films for the sensitivity, thin films for morphological discrimination), three films should be examined before making a judgment.

  • Quantitative buffy coat (QBV) can be used as quicker but less accurate tool. 

Management:

  • The drug of choice for susceptible, uncomplicated malaria parasite is chloroquine.

  • In case of P. vivax and P. ovale malaria successful treatment, a 2-3 weeks course of Primaquine to prevent relapses.

  • P. falciparum has identified resistance to chloroquine so combination of drugs should be used.

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  • Severe falciparum malaria is considered as medical emergency, IV artesunate is given. Intensive care may be needed. Severe anemia may urge transfusion.

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References:

  1. Kumar P,Clark M. Kumar and Clark’s Clinical Medicine. Sixth edition. UK. Elsevier Limited. 2009

  2. Autino B, Noris A, Russo R, Castelli F. EPIDEMIOLOGY OF MALARIA IN ENDEMIC AREAS. Mediterranean Journal of Hematology and Infectious Diseases. 2012;4(1):2012060.

  3. World Health Organization. Malaria in Saudi Arabia. http://www.who.int/malaria/publications/country-profiles/profile_sau_en.pdf

 

First author:  

Ahmad Ibrahim Aldayel


Reviewed by:    

Osama Wadaan

Abdulrahman Alhassan


Format Editor:  

Noura Abdullah Alsubaie