Malaria

What is malaria?

Malaria is an acute febrile infectious disease caused by protozoan parasites transmitted by vectors (mosquitoes). It is also known as: paludism, impaludism, marsh fever, intermittent fever, benign tertian fever, malignant tertian fever, and by popular names such as “maleita,” “sezão,” “tremedeira,” “batedeira,” or simply “fever.”

It is recognized as a serious global public health issue, affecting nearly 50% of the population across more than 109 countries and territories. The estimated annual number of new cases worldwide reaches 300 million, with 1 million deaths, mainly among children under 5 years old and pregnant women in Africa.

In Brazil, the Amazon region—particularly rural areas—is considered endemic for malaria, accounting for over 90% of reported cases, concentrated in nine states: Acre, Amapá, Amazonas, Pará, Rondônia, Roraima, Maranhão, Mato Grosso, and Tocantins.

Causes

In Brazil, three species of protozoa from the Plasmodium genus infect humans: Plasmodium malariae, Plasmodium vivax, and Plasmodium falciparum. The species Plasmodium ovale occurs only on the African continent; however, imported cases may occasionally be diagnosed in Brazil.

How does transmission occur?

Transmission occurs through the bite of a female mosquito belonging to the order Diptera, infraorder Culicomorpha, family Culicidae, and genus Anopheles. This mosquito must be infected with the Plasmodium protozoan. The Anopheles genus includes about 400 species worldwide, around 60 of which are found in Brazil.

In Brazil, the main species are: Anopheles (N.) darlingi, Anopheles (N.) aquasalis, and Anopheles (N.) albitarsis. These mosquitoes are popularly known as “carapaña,” “muriçoca,” “sovela,” “mosquito prego,” and “bicuda.” Bites are more frequent at dusk and dawn (crepuscular hours), but they can occur throughout the night.

Rarely, transmission can occur through blood transfusion or shared use of syringes, and congenital transmission is also uncommon.

The incubation period varies depending on the species of protozoan: P. falciparum (8 to 12 days), P. vivax (13 to 17 days), P. malariae (18 to 30 days).

Risk Factors

The conditions that influence disease transmission are related to the susceptible population, the etiological agent, the vector, and ecological, economic, social, and cultural factors. Risk factors are associated with exposure to bites from female mosquitoes in the Amazon region. Being over 65 years old, female sex (strongly linked to pregnancy), non-immune status, lack of antimalarial prophylaxis, and exposure to the vector are all risk factors for malaria.

Symptoms

The typical clinical presentation includes high fever (up to 41 °C), accompanied by chills and generalized shivering lasting from 15 to 60 minutes, profuse sweating, headache, nausea, and vomiting. These symptoms occur in cyclical patterns depending on the species of Plasmodium involved. Before the onset of fever, the patient may experience nausea, vomiting, weakness, fatigue, and loss of appetite. Signs of severe malaria include: Temperature > 41 °C, seizures, acute confusional state, hyperparasitemia (> 200,000/mm³), repeated vomiting, oliguria (acute kidney failure), shortness of breath, severe anemia, jaundice, hemorrhages and low blood pressure.

Is it possible to acquire immunity to the disease?

Reinfection is common among patients who remain in endemic areas, and after repeated infections, individuals develop a certain degree of immunity. When reinfected, they tend to present a milder form of the disease, often without symptoms, due to this acquired immunity.

Diagnosis

Diagnosis is only possible through the detection of the parasite or its antigens in the patient’s peripheral blood. The methods include: Thick blood smear (optical microscopy after staining with vital dyes such as methylene blue and Giemsa, used to evaluate morphology, different developmental stages of the parasite, and to determine parasitic density for prognostic assessment); Thin blood smear; Immunochromatographic tests or rapid diagnostic tests (these are not capable of detecting mixed malaria infections, i.e., infections caused by two different types of protozoa); Serological tests to detect IgG and IgM fractions: hemagglutination and indirect immunofluorescence.

Treatment

Malaria treatment aims to target the parasite at key stages of its life cycle, such as: interrupting blood-stage schizogony, destroying the parasite’s latent forms (hypnozoites), stopping parasite transmission, and preventing the development of sexual forms of the parasite. The treatment duration ranges from 3 to 14 days, depending on the species, and involves regimens that may include: chloroquine, primaquine, artesunate, artemether, mefloquine, lumefantrine, doxycycline, quinine, and clindamycin.

Is there a cure?

Yes, and it depends on choosing the appropriate treatment regimen and, most importantly, on the patient’s adherence to the treatment.

Complications

Among the complications, there is the potential progression to severe malaria and spontaneous rupture of the spleen.

Prevention

• early diagnosis and treatment help interrupt the transmission chain by reducing the number of female mosquitoes infected with Plasmodium after biting patients. In this sense, educating the population about the signs and symptoms of malaria and encouraging them to seek medical care is essential
• vector control through indoor residual spraying, thermal fogging with insecticides, and larval control by treating mosquito breeding sites
• on an individual level: use of mosquito nets (impregnated or not with insecticides), wearing clothing that covers arms and legs, installing screens on doors and windows, and using repellents
• guidance for travelers to endemic areas on individual preventive measures and restricted recommendation of prophylaxis with subtherapeutic doses of antimalarial drugs such as doxycycline, mefloquine, and chloroquine. In such cases, prophylaxis is only recommended when the risk of severe disease and/or death from P. falciparum malaria outweighs the risk of serious adverse effects from the drugs used

By the Einstein Editorial Board