Malaria: Causes, Symptoms, Transmission, and Prevention
Malaria
What is Malaria?
Malaria is an acute febrile infectious disease caused by a unicellular parasite. It is characterized by high fever, chills, sweats, and headaches, occurring in cyclical patterns depending on the infecting parasite species. An initial symptomatic phase, marked by malaise, headache, fatigue, and muscle pain, typically precedes the classic malaria fever.
Symptoms
The characteristic malaria paroxysm begins with chills lasting 15 minutes to an hour, followed by a fever phase with body temperatures reaching 41°C (105.8°F) or higher. After two to six hours, the fever subsides, leaving the patient with severe weakness and profuse sweating. Following the initial phase, the fever becomes intermittent, depending on the erythrocytic cycle of the Plasmodium species: 48 hours for P. falciparum and P. vivax (tertian malaria), and 72 hours for P. malariae (quartan malaria). However, this regular pattern is less common today.
Generally, P. vivax and P. malariae cause milder forms, while P. falciparum causes the most severe clinical forms, especially in non-immune adults, children, and pregnant women.
Severe and complicated malaria can manifest as severe headaches, fever, vomiting, drowsiness, seizures (cerebral malaria), acute renal failure, pulmonary edema, hypoglycemia, liver dysfunction, hemoglobinuria (acute massive intravascular hemolysis), and shock, potentially leading to death in about 10% of cases.
Transmission
Malaria is transmitted through the bite of an infected female Anopheles mosquito. Sporozoites, the infective forms of the parasite, are inoculated into a healthy person through the mosquito’s saliva. When these mosquitoes feed on infected individuals, they ingest gametocytes, which reproduce within the mosquito for 8 to 35 days. Sporozoites are then released during subsequent bites. The vector typically feeds during twilight, dusk, and dawn, although some Amazonian species exhibit nocturnal habits. Direct person-to-person transmission does not occur. Rare transmissions may occur through infected blood transfusions, shared syringes, or, even more rarely, congenitally.
Etiology, Reservoir, and Vector
- Etiologic Agent: In Brazil, three Plasmodium species cause malaria: P. malariae, P. vivax, and P. falciparum.
- Reservoir: Humans are the only significant reservoir.
- Vector: Mosquitoes of the genus Anopheles. In Brazil, the primary vectors are Anopheles darlingi, Anopheles aquasalis, Anopheles albitarsis, Anopheles cruzii, and Anopheles bellator, with Anopheles darlingi being the most prominent.
Incubation and Communicability
- Incubation Period: Varies depending on the Plasmodium species: P. falciparum (8–12 days), P. vivax (13–17 days), and P. malariae (18–30 days).
- Period of Communicability: A person can be infectious for varying durations: up to one year for P. falciparum, up to three years for P. vivax, and over three years for P. malariae.
Diagnosis and Treatment
Definitive diagnosis requires demonstrating the parasite or its antigens in peripheral blood. The Brazilian Ministry of Health provides free treatment drugs nationwide through the Unified Health System (SUS).
Epidemiology and Notification
Malaria is a significant public health concern, particularly in the Amazon region, where it causes substantial social and economic losses. All malaria cases must be reported to health authorities using the Malaria Case Notification Form (SIVEP-Malaria). Investigation is mandatory in the Extra-Amazonian Region.
Prevention and Control
Control measures include prompt treatment, contact tracing, epidemiological investigation, public health education, vector control with insecticides, and personal protective measures such as insect repellents, bed nets, protective clothing, and window screens.