Malaria is one of the world’s most common and deadly infectious diseases, consistently ranking in the top 10 leading causes of death in the developing world. It’s caused by a protozoan, not bacteria or viruses like other significant infectious diseases like Cholera, Tuberculosis, or HIV. According to the World Health Organisation (WHO), about 240 million people became infected with malaria in 2020, and 600,000 of them died. Despite successes in reducing the fatality rate by 25% during this century due to the development of effective prevention and treatment strategies, malaria incidences have been increasing since the 1970s. That’s why malaria remains one of the world’s biggest threats to public health, especially in tropical countries.

Malaria Definition

Malaria is a life-threatening disease caused by the Plasmodium parasite. The parasite is transmitted through bites from female Anopheles mosquitoes, which feed on human blood. When a mosquito bites an infected person, it can acquire the parasite, which multiplies inside the insect. The next time the mosquito bites, it can inadvertently inject the pathogen into an uninfected person.

Malaria is most common in tropical and subtropical regions, particularly sub-Saharan Africa, where approximately half of the world’s population lives at risk of contracting the disease. Children under 5 are particularly vulnerable, accounting for up to 80% of malaria-related deaths worldwide. The African continent is the hardest hit, accounting for 95% of all malaria cases and deaths. Four African countries - Nigeria, the DRC, Tanzania, and Mozambique - account for half of all worldwide malaria fatalities. It is crucial to prevent and treat malaria to reduce the burden of this deadly disease on vulnerable populations.

Causes of Malaria

Malaria is caused by five different species of the Plasmodium group, which are single-celled pathogens known as protozoans. These parasitic organisms can infect humans, animals, or plants. Plasmodium falciparum and Plasmodium vivax are the most dominant and pose the greatest threat to human health. Plasmodium falciparum is the deadliest malaria pathogen and is widespread in Africa. The other species include Plasmodium malariae, Plasmodium knowlesi, and Plasmodium ovale.

Malaria's asexual infective stage occurs when the parasite multiplies within human red blood cells. During this stage, the parasite excretes toxic waste substances such as hemozoin pigment or GPI into the red blood cell. Over time, these substances accumulate and are eventually released into the bloodstream when the infected red blood cell ruptures. The toxins stimulate the immune system, resulting in the clinical symptoms of malaria and further influencing the disease's pathophysiology. 

Malaria Symptoms

Malaria infection can cause a range of symptoms, dividing the disease into uncomplicated or severe (complicated) forms. The incubation period between an infective mosquito bite and symptom onset can range from a week to a year, but typically takes 10-15 days. In more aggressive cases, symptoms can appear as quickly as 24 hours after the bite. Shorter incubation periods are more common with Plasmodium falciparum infections.

Initial symptoms of malaria can be mild and flu-like, including fever, headaches, and chills, which can contribute to misdiagnosis. Other symptoms can include muscle pain, anemia, jaundice, increased respiratory rate, or spleen and liver enlargement. If left untreated, particularly in Plasmodium falciparum infections, symptoms can progress to severe illness, including organ failure and associated pathological manifestations such as acute kidney injury or acute respiratory distress syndrome, ultimately leading to death.

One severe manifestation of malaria is cerebral malaria, which is associated with high mortality rates. This condition causes neurological symptoms such as seizures, coma, and abnormal behavior. Cerebral malaria occurs when red blood cells infected with Plasmodium falciparum adhere to the lining of brain blood vessels, rather than circulating freely in the bloodstream. It is crucial to diagnose and treat malaria promptly to prevent severe illness and potential fatality.

Malaria Transmission

Malaria is primarily transmitted between infected and uninfected individuals through the bite of a female Anopheles mosquito. The mosquito feeds on human blood to obtain the necessary proteins and if the bitten person is infected with the malaria parasite, the mosquito becomes infected as well. The parasite grows and multiplies inside the insect, and when the mosquito feeds again, it releases the parasite into the bloodstream of the next bitten individual. The mosquito releases anticoagulants from its salivary glands to facilitate blood uptake, and the parasite is present in the insect's salivary glands, where it is released alongside the anticoagulants.

The female Anopheles mosquito is the malaria vector and does not suffer from being infected with the parasite. Malaria transmission requires cyclical infection of both humans and mosquitoes, as Plasmodium multiplies inside both hosts, increasing the chance of infecting other mosquitoes and humans. The life cycle of Plasmodium has two stages: a sexual stage in the mosquito and an asexual stage inside humans.

Upon infection, the malaria parasite enters the bloodstream and initially targets liver cells, followed by red blood cells, multiplying inside both. Most pathological manifestations result from the erythrocyte infection stage, where the parasite repeatedly lyses red blood cells and invades other red blood cells cyclically. Malaria can also be transmitted between individuals through re-using unsterile needles during blood transfusions (transfusion-transmitted malaria) or from mother to fetus during pregnancy (congenital malaria), although these are less common. In congenital malaria, the parasite is directly transmitted by infected mothers across their placenta either before or during their delivery. 

Difference Between Yellow Fever and Malaria

Malaria and yellow fever are two different febrile mosquito-borne diseases that are sometimes confused with each other, despite having distinct differences. Malaria is caused by the protozoan Plasmodium pathogen transmitted via the female Anopheles mosquito, while yellow fever is caused by a virus, specifically an arbovirus of the flavivirus genus, transmitted by mosquitoes of the Haemogogus and Aedes species.

While both diseases are common in tropical African and South American countries, malaria is far more deadly than yellow fever. A severe case of yellow fever can be mistaken for malaria as both diseases are hard to diagnose and have initial fever-like symptoms. However, yellow fever does not have any specific drug treatment available, as no specific antiviral drugs exist to target the yellow fever viral pathogen. Despite this, most people tend to recover within a few days with supportive treatment.

Malaria Treatment

Malaria is a treatable and curable disease. Early diagnosis and treatment are important to reduce malaria incidence and deaths. The World Health Organization (WHO) recommends that malaria diagnosis be done through microscopical blood analysis for parasite detection or by using rapid diagnostic tests that rely on antigen detection. An accurate and early diagnosis helps distinguish a malaria fever from other febrile illnesses allowing for more effective treatments and better surveillance.

Malaria treatments include the antimalarial drugs quinine and chloroquine, which prevent the parasite from growing and spreading within the body by inhibiting its protein synthesis. These drugs can also be used as prophylactics (preventive drugs) to stop an infection from occurring if a person gets bitten by an infected mosquito. The best treatment available is artemisinin-based combination therapy (ACT), especially for Plasmodium falciparum infection.ACT works by rapidly eliminating the malaria pathogen from the bloodstream, thus stopping disease progression.

Besides prophylactic drugs, two other important preventive measures play a significant role in helping the global effort to control malaria. These are vector control strategies and the malaria vaccine. Vector control strategies include efforts to either reduce the number of malaria vector mosquitos or avoid getting bitten by them. The most important strategies in vector control are the use of insecticide-treated bed nets to protect against mosquito bites during sleep, insect-repellent spraying, or other insecticide usages that help kill infective mosquitoes.

Resistance to antimalarial drugs usually occurs whenever a treatment is used extensively to kill a pathogen. Antimalarial drug resistance has emerged as a serious problem in tackling malaria. Resistance to chloroquine, for example, has emerged, with drug-resistant Plasmodium strains appearing throughout South America and Africa. Surveillance is paramount to detect these events and inform the treatment policy promptly.

Since late 2021, the WHO has recommended using the first approved malaria vaccine RTS,S (Mosquirix), among children. This vaccine acts against Plasmodium falciparum and significantly reduces severe malaria disease in children.⁵ This new important tool will undoubtedly be very important to help meet the WHO Global Malaria program objective of reducing by at least 90% the incidence and mortality rates of malaria by 2030. 

Malaria - Key Takeaways

Malaria is a febrile infectious disease caused by protoctist Plasmodium parasites that infect and are transmitted between humans via female Anopheles mosquito bites. Malaria is caused by five different species of the Plasmodium group, and its pathophysiology is mostly explained due to the infection and destruction of human red blood cells. Symptoms of malaria are often flu-like, such as fever and headaches, while severe clinical manifestations include cerebral malaria and liver enlargement. Malaria treatments include the antimalarial drugs quinine and chloroquine as well as artemisinin-based combination therapy (ACT). Vaccine administration and vector control strategies, such as bed nets are currently being used to reduce malaria incidence.

Malaria

What is malaria?

Malaria is an acute febrile infectious disease caused by Plasmodium group parasites. 

What type of pathogen causes malaria?

Protoctist Plasmodium parasite species, also called protozoans.

How is malaria spread?

Malaria is transmitted between humans via the female anopheles mosquito. Mosquitos bite humans to feed on their blood. If the bitten person is infected, the mosquito will also become infected with the malaria Plasmodium pathogen once they bit. The infected mosquito will go on to infect other humans that she bits.

What causes malaria?

Malaria is caused by five different species of the Plasmodium group. The pathogen infects and destroys the human host's red blood cells.

What is the difference between yellow fever and malaria?

Malaria is caused by the protozoan Plasmodium pathogen transmitted via the female anopheles mosquito. Yellow fever is caused by an arbovirus of the flavivirus genus transmitted by mosquitos of the Haemogogus and Aedes species.

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