Remember to think of malaria: an old world disease, a new world threat

Malaria is a protozoan parasitic disease caused by in­fection of the red blood cells with one (rarely two) species of the genus Plasmodium: Plasmodium falciparum, P. vivax, P. ovale or P. malariae. 

Malaria was first described in the scientific literature in the early 18th century, but it wasn’t until 1902 that Sir Ronald Ross identified that it was transmitted by mosquitoes. Ma­laria is a major public health problem worldwide. Over 2.4 billion people in more than 90 countries—40% of the world’s population—are at risk from this infection. The worldwide prevalence of this disease is estimated to be about 300 million to 500 million cases per year with an estimated 1 million deaths; more than 90% of cases are in sub-Saharan Africa. 

While the mosquito vectors are not present in British Columbia, travel to malaria endemic areas is common. Returning travelers may come home with more souvenirs than plan­ned, and it is crucial for physicians to remember to think of this disease in patients with fever returning from endemic areas, since it is a potentially life-threatening illness.

Clinical presentations
Taking a travel history is critical. In­for­mation about which countries, and which areas within each country, known to be endemic for malaria is available online (www.cdc.gov/malaria/). 

Symptoms usually start within 5 to 16 days (varies from species to species) after being bitten by a malaria-infected mosquito. Patients present with fever, chills, sweats, headache, weakness, and malaise—basically, a flu-like illness. 

Severe disease may develop, most often following infection with P. falciparum. Severe ma­laria due to P. falciparum, including cerebral malaria with decreased level of consciousness and other neuro­logical symptoms, may present with pulmonary edema, severe anemia, and renal failure. A combination of these complications is possible. 

In severe falciparum malaria, red cells parasitized by falciparum may cause obstruction of capillaries and post-capillary venules, leading to local hypoxia, and have the complications of this disease. Infections due to P. falciparum also may progress quickly because this species multiplies rapidly in the blood. Infections due to this species should be considered a potential medical emergency.

Laboratory diagnosis 
Samples of peripheral blood (collected from the ear lobe or fingertip) during febrile periods are required. Microscopic examination of thick and thin Giemsa-stained smears of this blood (repeated over several days if the initial smears are negative), re­main the best way to diagnose malaria. 

A thick smear allows medical laboratory technologists to identify even low levels of parasitemia. Examination of thin smears is used for speciation and estimation of the number of parasites present in the blood. Antigen detection tests are also useful, particularly in laboratories where diagnostic experience is limited.

Prevention and treatment
Malaria control in endemic communities depends upon the elimination of mosquitoes, a global challenge. Personal protection, use of prophylactic (suppressive antimalarial therapy) medications, and early treatment of cases are all important to preventing infections.

The widespread resistance of P. falciparum to chloroquine complicates the treatment of falciparum malaria. When malaria is acquired in areas with known chloroquine resistance, a combination of atovaquone and proguanil, or quinine and tetracycline, or doxycycline and clindamy­cin, may be considered as the possible options. Chloroquine remains highly effective against P. malariae and P. ovale malaria, as well as P. vivax acquired everywhere except in Papua New Guinea and parts of Indonesia. Infections caused by P. vivax and P. ovale require a follow-up course of primaquine to eradicate latent liver forms that may cause subsequent relapses.

Summary
Malaria is a potentially fatal infection that physicians in BC should consider in febrile, returning travelers. Collection of peripheral blood samples during febrile periods for both thick- and thin-stained smear examination by experienced technologists must be performed as STAT testing in Re­gional Health Authority Laboratories. 

The BCCDC Laboratory Services on-call medical microbiologist (604 661-7033) works with regional medical microbiologists or pathologists to expedite requests for assistance in the speciation of the malaria parasite or further investigation of this disease. Malaria is a reportable communicable disease in BC and both physicians and laboratories are reminded to report this infection to public health.

—Muhammad Morshed, PhD, SCCM 
—Quantine Wong, BSc 
—Judith L. Isaac-Renton, MD, DPH, FRCPC
BC Centre for Disease Control Laboratory Services, PHSA

Further reading
1. Griffith KS, Lewis LS, Mali S, et al. Treatment of malaria in the United States: A systematic review. JAMA 2007;297:2264-2277. 

 2. Tampuz A, Jereb M, Muzlovic I, et al. Clinical review: Severe malaria. Crit Care 2003;7:315-323. Available online: http://ccforum.com/content/7/4/315.

Muhammad Morshed, PhD, SCCM, Quantine Wong, BSc, Judith Isaac-Renton, MD, DPH, FRCPC. Remember to think of malaria: an old world disease, a new world threat. BCMJ, Vol. 50, No. 3, April, 2008, Page(s) 163 - BCCDC.



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