Malaria

Malaria is a mosquito-borne infectious disease that affects humans and other vertebrates across tropical and subtropical regions. It is transmitted exclusively through the bite of infected female Anopheles mosquitoes, which introduce Plasmodium parasites into the bloodstream. The disease is characterised by recurring fever, rigours, fatigue and flu-like symptoms, and in severe cases can lead to life-threatening complications affecting major organs. Malaria remains one of the world’s most significant public health challenges, with the highest burden concentrated in sub-Saharan Africa and parts of Asia and Latin America.

Biology of the Parasite and Transmission

Malaria is caused by protozoan parasites of the genus Plasmodium. The infection begins when an infected mosquito injects sporozoites from its saliva into human blood. These parasites travel to the liver, where they mature and multiply. After this initial stage, thousands of merozoites are released back into the bloodstream, invading red blood cells and continuing cycles of replication.
Five species commonly infect humans:

• P. falciparum – responsible for most severe disease and the majority of global malaria deaths.
• P. vivax – widespread and capable of forming dormant liver stages that reactivate months later.
• P. knowlesi – a zoonotic parasite normally infecting macaques, now causing increasing numbers of human infections in Southeast Asia.
• P. ovale – generally associated with milder illness.
• P. malariae – causes chronic, low-grade infections.

Although the parasites multiply within humans, transmission occurs only through the mosquito vector, making vector ecology a central factor in the spread of the disease.

Signs, Symptoms and Clinical Presentation

Symptoms typically begin 10–15 days after the infective mosquito bite, though some strains, particularly P. vivax, may cause delayed onset due to dormant liver stages. The early presentation resembles influenza, with fever, chills, headache, vomiting, myalgia and malaise. Recurrent cycles of fever are a hallmark of malaria, known as paroxysms, and occur as infected red blood cells rupture. Patterns vary among species:

• Every 48 hours in P. vivax and P. ovale.
• Every 72 hours in P. malariae.
• Irregular or near-continuous fevers in P. falciparum.

Children often exhibit non-specific symptoms such as coughing, diarrhoea or poor feeding.
Severe malaria, most commonly caused by P. falciparum, can manifest within 9–30 days of infection. Complications include:

• Cerebral malaria, featuring seizures, coma, abnormal posturing and neurological deficits.
• Severe anaemia due to rapid destruction of red blood cells.
• Respiratory distress, which may arise from metabolic acidosis or pulmonary oedema.
• Kidney failure, including blackwater fever marked by dark urine due to haemoglobin loss.
• Disseminated bleeding and circulatory collapse.
• Retinal changes, helpful for distinguishing cerebral malaria from other encephalopathies.

Pregnancy-associated malaria increases the risk of miscarriage, stillbirth, low birth weight and maternal complications.

Diagnosis

Diagnosis traditionally relies on microscopic examination of stained blood films, enabling confirmation of infection and identification of the Plasmodium species. Rapid diagnostic tests (RDTs), which detect parasite antigens, are widely used in endemic areas due to their simplicity and speed.
More advanced methods, including polymerase chain reaction (PCR) tests, offer greater sensitivity but are less accessible in routine clinical practice in high-burden regions because of cost and laboratory requirements.

Prevention and Control

Malaria prevention centres on reducing human–mosquito contact and controlling mosquito populations. Key measures include:

• Insecticide-treated mosquito nets.
• Indoor residual spraying with insecticides.
• Elimination of standing water to curb breeding sites.
• Use of insect repellents.

Chemoprophylaxis is recommended for travellers to endemic regions, with regimens tailored to destination and resistance patterns. In areas with high transmission, intermittent preventive treatment using sulfadoxine–pyrimethamine is advised for infants and pregnant women after the first trimester.
As of 2023, the World Health Organization has endorsed two malaria vaccines, marking a major milestone in preventive public health, particularly for children in Africa.

Treatment

The preferred treatment for uncomplicated malaria is artemisinin-based combination therapy (ACT). These regimens pair artemisinin derivatives with partner drugs such as lumefantrine, mefloquine or sulfadoxine–pyrimethamine to enhance efficacy and reduce resistance. When artemisinin derivatives are unavailable, quinine combined with doxycycline or other adjunct medications may be used.
Confirmation of malaria prior to treatment is encouraged in high-burden regions to avoid unnecessary drug exposure and slow the development of drug resistance. Resistance to several antimalarials has emerged, including widespread chloroquine resistance and growing artemisinin resistance in Southeast Asia.

Distribution and Global Burden

Malaria is endemic in tropical and subtropical regions across a wide equatorial belt, particularly in:

• sub-Saharan Africa,
• South Asia and Southeast Asia,
• parts of Latin America and Oceania.

In 2023, approximately 263 million cases of malaria resulted in an estimated 597,000 deaths worldwide, with about 95% of cases and deaths occurring in sub-Saharan Africa. The disease exacts a profound toll on young children: in 2021, nearly one child under five died every minute, despite the availability of effective prevention and treatment.
Though malaria was once widespread in Europe and North America, it is now non-endemic in these regions, with occasional imported cases among travellers.

Economic and Social Impact

Malaria remains closely linked with poverty. The disease reduces productivity, increases healthcare spending and undermines long-term economic growth. In Africa, losses are estimated at over USD 12 billion annually, driven by treatment costs, reduced labour capacity and the impact on tourism.
India has seen significant progress: between 2017 and 2023, recorded malaria cases fell by 69%, and estimated deaths dropped by 68%, illustrating the impact of sustained public health measures.

Etymology and Historical Context

The word malaria derives from the Medieval Italian mala aria (“bad air”), reflecting the pre-modern belief that the disease arose from foul vapours in marshlands. Historical names such as ague and marsh fever also reveal early associations with swampy environments. The disease was common in Europe and parts of North America until the twentieth century, when public health interventions eliminated local transmission.
The scientific study of malaria, known as malariology, has advanced understanding of the parasite’s lifecycle, its interaction with mosquito vectors and the ecological factors that influence transmission.
Malaria remains a major global health challenge, but sustained prevention, effective treatment, expanding vaccination and international coordination continue to reduce its impact and offer hope of long-term control.