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Image: CDC - Global Health Division of Parasitic Disease
Malaria is a mosquito borne illness caused by eukaryotic protist parasites of the genus Plasmodium. Dr. Charles Louis Alphonse Laveran discovered Plasmodium in 1880. His discovery was made after drawing blood from a cyclically febrile patient, using the microscope for investigation. For this, Laveran was awarded the Nobel Prize in 1907.
Malarial disease results from multiplication of malarial parasites within red blood cells. Female mosquitoes of the Anopheles genus are the primary hosts of this parasite. Mosquitoes act as transmission vectors while humans act as secondary hosts. In the anopheles genus, only females feed on blood. Males feed on plant nectar and are therefore benign in the disease cycle.
Topographic description of malarial transmission world wide. For a detailed look at Malaria across the globe use the Malaria Map Application found on at the US Center for Disease Control.
|This thin film blood smear micrograph depicts an immature Plasmodium malariae schizont.
Photo by CDC/ Dr. Mae Melvin, 1965
There are two phases of malaria pathogenesis: 1) the exoerythrocytic phase, that which takes place outside of the red blood cell, and 2) the erythrocytic phase.
--> The female Anopheles mosquito becomes infected with malarial parasite.
--> Malaria sporozoites develop within the salivary glands of the mosquito.
--> The mosquito pierces human skin from dusk to dawn searching for a blood meal.
THIS MARKS THE BEGINNING OF THE EXOERYTHROCYTIC PHASE
--> Sporozoites from mosquito saliva enter the human (secondary host).
--> Sporozoites gain vascular entry and migrate to human liver.
--> Sporozoites infect hepatocytes immediately.
--> Asexual multiplication occurs within hepatocytes for a period of 8 – 30 asymptomatic days.
--> Sporozoites differentiate within hepatocytes to yeild thousands of merozoites.
--> Rupture of hepatocyte host cells with merozoite escape into blood.
--> Further erythrocyte infection
THIS MARKS THE BEGINNING OF THE ERYTHROCYTIC PHASE
--> Asexual multiplication within erythrocyte
--> Periodic rupture of RBCs to invade fresh hosts
--> Continuous amplification of exoerythrocytic and erythrocytic host cycles.
It is the cyclic ruptures and dissemination that cause cyclical fevers, chills and rigors.
Following a bite from a female Anopheles mosquito infected with malaria, inoculated sporozoites seek the liver within 1 to 2 hours. Most humans are asymptomatic for 8-30 days.
The classic symptoms include sudden onset chills, rigors, diaphoresis, followed by recurrent fever every 24 – 48 hours. Fevers usually last 4-6 hours, but can present as low grade but constant for days.
Early diagnosis of malaria and prompt effective treatment, reduces morbidity and mortality. See below for a listing of anti-malarial agents.
Initial symptoms are nonspecific. Most patients will have/develop uncomplicated disease. Consider malaria in patients who have travelled or lived in endemic areas who presents with:
Splenic enlargement is a common finding in endemic areas. This may represent repetitive infection. Repeat infections may lead to splenic infarctions causing splenic fibrosis.
These patients may have hyperparasitemia > 100,000 parasites/microl of blood) or >5 to 10 percent of parasitized RBCs. The World Health Organization uses the latter as diagnostic criteria for diagnosis of 'severe malaria'. Parasitized RBCs adhere to small blood vessels causing microinfarctions sparing no organ system.
In BC, order at any lab:
PCR testing is not used.
Giemsa stained blood smears are interpreted by light microscopy. With this technique however, diagnostic errors do occur in the setting of parasitemia of low-density. Microscopy allows for 1) calculation of parasitemia and 2) detection of Plasmodium species. Parasitic load is important for monitoring response to therapy. When rapid diagnostic testing is available, microscopy should be used as an adjunct. Microscopy is also useful for the diagnosis of other infectious agents which may be present in the setting of a malaria work up. These include Borrelia Recurrentis, Filariasis, Trypanosomiasis.
RDTs were introduced in the 1990s. These utilize immunochromatographic lateral flow technology.
Accurate diagnosis of malaria is important for appropriate therapy. Empiric treatment of malaria with chloroquine is no longer appropriate. The emergence of chloroquine-resistant P. falciparum is epidemic. Today, Artemisinin combination therapies are the mainstay of treatment. These however are expensive. Thus, accurate diagnosis is essential.
(Information retrieved from the US CDC)
Antimalarial drugs are used for both the prophylaxis and treatment of malarial disease.
Scientists have discovered immunity in many persons living in endemic areas of Africa. The degree of immunity directly correlates to degrees of parasitemia. Those living in Sub-Saharan Africa tend to develop complete immunity by the time of adulthood. Endemic areas of low transmission are shown to develop semi-immunity.
The counterfeiting of anti-malarials is a significant and growing problem worldwide.
Surveys of anti-malarial medications purchased in southeast Asia indicate that 30 – 50 percent of medications were counterfeit. Counterfeit medications often contain subtherapeutic amounts of active drug. Some counterfeit medications have been shown to contain no active compound.
Check out the WHO's Malaria Report 2010. This report discusses the World Health Assembly (WHA) malaria targets, and the international progress being made. The report is created using information received from 106 malaria endemic countries around the globe.
To learn more about World Malaria Day search here.
Dondorp AM, Newton PN, Mayxay M, et al. Fake antimalarials in Southeast Asia are a major impediment to malaria control: multinational cross-sectional survey on the prevalence of fake antimalarials. Trop Med Int Health 2004; 9:1241.
Newton P, Proux S, Green M, et al. Fake artesunate in southeast Asia. Lancet 2001; 357:1948.
Newton PN, Fernández FM, Plançon A, et al. A collaborative epidemiological investigation into the criminal fake artesunate trade in South East Asia. PLoS Med 2008; 5:e32.
WHO – World Malaria Report 2010
Translated educational handouts on health issues.
Dentists, physiotherapists and other community resources who speak other languages, accept IFH or offer reduced fees.
An overview of the main countries from which Canada receives refugees, with a focus on political and health issues.