Overview
Malaria is a parasitic disease caused by protozoa of the genus Plasmodium and transmitted to humans through the bite of an infected female Anopheles mosquito. Four species commonly infect humans: Plasmodium vivax, Plasmodium falciparum, Plasmodium malariae, and Plasmodium ovale, with P. vivax and P. falciparum being the most prevalent. After transmission, the parasite undergoes an asexual cycle in humans and a sexual cycle in the mosquito. In humans, sporozoites first invade liver cells, where hepatic schizogony occurs, followed by invasion of red blood cells, leading to erythrocytic schizogony. The rupture of infected red blood cells releases merozoites and malaria toxins, which are responsible for clinical symptoms. P. falciparum is associated with severe disease due to cytoadherence of infected red cells in capillaries of vital organs.
Symptoms
It typically presents with characteristic febrile paroxysms consisting of three stages: cold stage, hot stage, and sweating stage. The cold stage is marked by chills, shivering, and a feeling of intense cold. This is followed by the hot stage, characterized by high-grade fever, headache, nausea, vomiting, and restlessness. The sweating stage is followed by profuse sweating and a rapid fall in temperature, leading to exhaustion. These paroxysms usually recur every 48 hours in P. vivax, P. falciparum, and P. ovale infections and every 72 hours in P. malariae infection. Other common symptoms include anemia, pallor, splenomegaly, myalgia, joint pains, thrombocytopenia, and hypoglycemia. Severe falciparum malaria may lead to cerebral malaria, presenting with convulsions, coma, and sometimes death.
Causes
It is caused by infection with Plasmodium parasites transmitted by the bite of an infected female Anopheles mosquito. Transmission occurs when sporozoites present in mosquito saliva enter the bloodstream during a blood meal. Less common modes of transmission include blood transfusion, use of contaminated needles or syringes, and congenital transmission from mother to fetus. The clinical manifestations are caused by cyclic rupture of parasitized red blood cells during erythrocytic schizogony, leading to the release of merozoites and toxic metabolites. In P. falciparum infection, sequestration of infected red cells in capillaries causes impaired microcirculation and severe complications such as cerebral malaria and blackwater fever.
Risk Factors
Risk factors include residence in or travel to endemic areas, lack of acquired immunity, poor socioeconomic conditions, inadequate mosquito control measures, and increased exposure to mosquito bites. Children, pregnant women, non-immune travelers, and immunocompromised individuals are at higher risk of severe disease. Overcrowding, poor housing, stagnant water sources, and lack of access to healthcare increase transmission risk. P. falciparum infection carries a higher risk of complications such as severe anemia, cerebral malaria, renal failure, and blackwater fever.
Prevention
Prevention focuses on interrupting transmission and early diagnosis with prompt treatment. Vector control measures such as elimination of mosquito breeding sites, use of insecticide-treated bed nets, indoor residual spraying, and personal protective measures reduce mosquito exposure.
Chemoprophylaxis is recommended for travelers to endemic areas. Early diagnosis using microscopic examination of thick and thin blood smears remains the gold standard, supported by rapid diagnostic tests and molecular methods. Timely and effective antimalarial treatment prevents complications, reduces transmission, and lowers mortality associated with malaria.
