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Malaria

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Biology

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. Unlike other significant infectious diseases like Cholera, Tuberculosis or HIV, malaria is not a bacterial or viral infectious disease. Malaria is one of the most significant infectious diseases not caused by bacteria or viruses. Malaria’s causative pathogenic agent is a protozoan.

According to the World Health Organisation (WHO), about 240 million people became infected with malaria, of which about 600,000 died in 2020 alone. 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. As such, malaria remains one of the world’s biggest threats to public health, especially in tropical countries.

Malaria Definition

Malaria is an infectious disease caused by the Plasmodium parasite. Malaria is transmitted between individuals via the female mosquito Anopheles. This mosquito bites humans to feed on their blood. If the bitten person is infected with malaria, the mosquito can inadvertently also collect the pathogen, which multiplies inside the mosquito. Anopheles mosquitoes can carry Plasmodium without becoming sick. The plasmodium infection is kept under control by the mosquito’s immune system, but when the infected insect feeds again, it will inject the pathogenic microorganism into an uninfected person.

Malaria is a life-threatening acute febrile infectious disease caused by protoctist Plasmodium parasites that infect and are transmitted between humans via mosquito bites.

Approximately half of the world’s population currently live in regions where they are at risk of contracting malaria. Malaria incidence is bigger throughout the tropics and subtropical regions, particularly sub-Saharan Africa. Up to 80% of malaria’s victims are children under 5, making this infectious disease one of the leading causes of child mortality worldwide.

The African continent accounts for 95% of all malaria cases and deaths, making this region disproportionately suffer the burden of malaria disease. Four African countries alone including Nigeria, the DRC, Tanzania, and Mozambique, account for half of the worldwide malaria fatalities.

Causes of Malaria

Malaria is caused by five different species of the Plasmodium group. Plasmodium microorganisms are protoctist single-cell pathogens, also called protozoans. This group of pathogens are eukaryotic parasitic organisms that can infect humans, animals or plants. Two of the five parasitic species, Plasmodium falciparum and Plasmodium vivax, are the most dominant; therefore, the greatest threat. Plasmodium falciparum, in particular, is the deadliest malaria pathogen and the most widespread in the African region. The other species include Plasmodium malariae, Plasmodium knowlesi and Plasmodium ovale.

Eukaryotic cells contain membrane-bound organelles, such as the nucleus.

Malaria disease is essentially caused by the asexual infective stage of the parasite when it lives within the human red blood cells. The parasite multiplies and excretes several toxic waste substances into the red blood cell, like the hemozoin pigment or GPI. These substances accumulate within the red blood cell and are eventually released into the bloodstream when the infected erythrocyte lysates. The released toxins then stimulate the immune system, creating many of the feature clinical symptoms of malaria and further influencing the pathophysiology of this disease.

Malaria Symptoms

Malaria infection can result in various symptoms, often dividing malaria into uncomplicated or severe (complicated) diseases. Following the infective mosquito bite, there is an incubation period before symptoms appear that can range from a week to a year, but, on average, it takes 10-15 days. In some aggressive cases, malaria symptom onset can occur as fast as 24 hours after the infective mosquito bite. Shorter incubation periods are more common with the more dominant Plasmodium falciparum parasite.

The incubation period refers to the time taken for the clinical manifestations of a disease to appear after exposure to a pathogen.

Initial symptoms of malaria may be mild and unspecific, like fever, headaches, and chills, making it harder to diagnose. The initial flu-like symptoms contribute to the misdiagnosis of this infectious disease. Other more advanced clinical features of malaria include muscle pain, anaemia, jaundice, increased respiratory rate or spleen and liver enlargement. If left untreated and especially in Plasmodium falciparum infection, symptoms can quickly progress to severe illness. In the more severe forms of malaria disease caused by this parasite species, the infection is often complicated by organ failures and associated pathological manifestations like acute kidney injury or acute respiratory distress syndrome, ultimately leading to death.

Severe manifestations of malaria disease can include, for example, cerebral malaria. This condition, often associated with high mortality, has several neurological symptoms like seizures, coma and abnormal behaviour. Cerebral malaria is caused when erythrocytes infected with Plasmodium falciparum adhere to the lining of brain blood vessels instead of freely circulating in the blood.

Malaria Transmission

Malaria is typically transmitted between infected and uninfected people via the female Anopheles mosquito. This vector insect bites humans to feed on their blood to obtain the necessary proteins. If the bitten person is infected with the malaria parasite, the mosquito will also become infected while collecting the blood. The parasite will then grow and multiply inside the insect. When the mosquito feeds again, it will also release the parasite into the bloodstream of the bitten individual. Every time the mosquito feeds, it releases anticoagulants from its salivary glands into the bloodstream to facilitate blood uptake. The parasite is present in the insect’s salivary glands and is therefore released alongside the anticoagulants.

Vectors are organisms that carry the infectious disease pathogen between people or between animals and humans. The insect female Anopheles mosquito is the malaria vector and does not suffer from being infected with the parasite.

Anticoagulants are agents that prevent blood clotting, effectively ‘thinning’ the blood.

Malaria transmission, therefore, requires cyclical infection of both humans and mosquitoes. Plasmodium multiplies inside both hosts and increases the chance of infecting other mosquitos and humans. Plasmodium’s life cycle has two stages: a sexual stage in the mosquito and an asexual stage inside humans.

Upon infection, the malaria pathogen 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. In this step, the parasite repeatedly lyses the red blood cells it was growing inside and invades other red blood cells cyclically.

In other less common cases, malaria can also be transmitted between individuals by re-using unsterile needles during blood transfusions (transfusion-transmitted malaria) or from mother to foetus during pregnancy (congenital malaria). 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 is sometimes confused with yellow fever, another febrile mosquito-borne disease, but these are two different infectious diseases. Despite both being common in tropical African and South American countries, malaria is far more deadly than yellow fever. Malaria is caused by the protozoan Plasmodium pathogen transmitted via the female anopheles mosquito. Yellow fever is caused by a virus, more specifically an arbovirus of the flavivirus genus, transmitted by mosquitos of the Haemogogus and Aedes species.

A severe case of yellow fever can be mistaken for malaria as both diseases are hard to diagnose and have initial fever-like symptoms. Yellow fever, unlike malaria, however, 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 of 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 WHO guidelines recommend 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.

Check out our Protein Synthesis article!

According to the WHO, 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 that drug 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. The appearance of antimalarial drug-resistant Plasmodium strains, and insecticide (DDT) resistant mosquitoes, were essentially the reason the WHO was unable to eradicate this disease throughout the past century, despite continuous efforts.

Lastly, 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. 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.

Check out our Vaccine article!

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. 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

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

Protoctist Plasmodium parasite species, also called protozoans.

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.

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

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.

Final Malaria Quiz

Question

Malaria is a bacterial infectious disease. True or False?

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Answer

False

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Question

Malaria is caused by what organism species?

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Answer

Plasmodium

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What is a vector?


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Answer

Vectors are organisms that carry the infectious disease pathogen between people or between animals and humans.

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Question

What cells does the malaria pathogen first attack in humans?


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Answer

Liver cells

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Question

What is cerebral malaria?

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Answer

Malaria condition that affects the brain causing neurological symptoms like seizures, coma and abnormal behaviour.

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What are the initial symptoms of Malaria disease?


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Answer

Fever, headaches and chills.

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There is no vaccine for malaria. True or False?


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Answer

False

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Question

What are the hemozoin pigment and GPI?


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Answer

Toxic waste substances released by the malaria pathogen into the red blood cells.

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Question

How does chloroquine work as an antimalarial drug?

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Answer

Prevent the parasite from growing and spreading in humans by inhibiting its protein synthesis.

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Explain vector control.


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Answer

Strategies used to reduce the number of malaria vector mosquitos or to avoid getting bitten by them.

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What is the WHO-recommended treatment for malaria?


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Answer

Artemisinin-based combination therapy (ACT).

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Question

Identify vector control strategies.


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Answer

Insecticide-treated bed nets; insect repellent spraying or other insecticide usages.

 

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Question

What is congenital Malaria?


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Answer

Malaria is transmitted from infected mother to fetus during pregnancy.

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What region of the world has a higher malaria incidence?


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Answer

Tropical and subtropical regions in particular in sub-Saharan Africa.

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Question

Most of malaria’s victims are children. Ture or False?


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Answer

True

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