What is Malaria?
Malaria is a serious mosquito-borne disease caused by Plasmodium parasites, which transmit to people through the bites of infective female Anopheles mosquitoes. The mosquito transmission cycle of malaria begins with the release of immature forms of the plasmodium, or sporozoites, into the bitten person’s bloodstream through the saliva of infective mosquitoes. After plasmodium enters the body, it travels to the liver of the host to mature into a form called schizonts which then multiply excessively into a form called merozoites. Once plasmodium parasites take the form of merozoites, they reenter the bloodstream to infect and ultimately rupture red blood cells.
What causes Malaria?
Plasmodium parasites are protozoan microorganisms. There are five species of Plasmodium that are known to cause malaria in humans, which are Plasmodium vivax, P. ovale, P. malariae, and P.knowlesi. Among these, the deadliest malaria parasite is P. falciparum, while whereas P. vivax, P. ovale, and P. malariae usually cause milder disease. P. falciparum is most common in Africa whereas P.vivax is typically the dominant Plasmodium species outside of Sub-Saharan Africa, and the most common malaria parasite worldwide. P.knowlesi was previously thought to predominantly affect Old World monkeys. In 2008, however, it was discovered that P.knowlesi was responsible for around 70 percent of cases of malaria in humans in some regions of Southeast Asia. Moreover, researchers have found that P. knowlesi could be easily mistaken for P. malariae during microscopic examination, leading to the attribution of many cases caused by P. knowlesi to P. malariae.
Is Malaria contagious?
Malaria does not transmit through contact or sexual intercourse. As mentioned above, the primary transmission route of malaria involves the bite of infected female Anopheles mosquitoes. Still, as plasmodium infects the red blood cells of the infected person, malaria can also be transmitted through blood transfusions, organ transplants, or contaminated devices such as needles and syringes. Finally, malaria can transmit to the infant from the mother prior to or during birth.
How common is Malaria?
Although malaria is relatively uncommon in temperate climates, it is still prevalent in many tropical and subtropical regions of Africa, Asia, and Latin America. According to World Health Organization (WHO), there were an estimated 241 million cases of malaria and 627,000 malaria-caused deaths. Moreover, the same report demonstrates that approximately 95% of all malaria cases and 96% of malaria-caused deaths occurred Sub-Saharan Africa, where Nigeria (31.9%), the Democratic Republic of the Congo (13.2%), United Republic of Tanzania (4.1%) and Mozambique (3.8%) were home to more than half of all malaria deaths.
What are the signs and symptoms of Malaria?
The signs and symptoms of malaria usually develop within a few weeks following the initial exposure to the parasite. However, in some cases, plasmodium can lay dormant within the body of the host for as long as years without causing any symptoms. If left untreated, infections with P. vivax or P. ovale may remain in the liver stage for years, and cause relapses after months or even years without symptoms. Likewise, another type of plasmodium, P. malariae, may remain the blood of its host for as long as several decades.
Common signs and symptoms of malaria may include fever, chills, headaches, fatigue, muscle pain, nausea, and vomiting, enlarged liver, mild jaundice, rapid breathing, abdominal pain, diarrhea, cough, and anemia. The symptoms, especially fever, may be experienced as attacks in cycles recurring every second or third day. The cycle typically starts with shivering and chills, followed by fever, headaches, and nausea, before terminating with a sweating stage and returning to normal.
In more severe cases of malaria, the infection can cause damage to internal organs resulting in severe anemia, blood in urine, blood clotting problems, impaired consciousness, metabolic acidosis, seizures, and coma. If left untreated, malaria can cause serious complications such as liver failure, kidney failure, pulmonary edema, dehydration, acute respiratory distress syndrome, and cerebral malaria, or lead to death.
How is Malaria diagnosed?
Malaria can be easily diagnosed with a simple blood test usually in the form of a blood smear or antigen-based rapid diagnostic test. With only a drop of blood, the test can not only detect the presence of a malaria infection, but also identify the type of plasmodium that is responsible for the infection. The blood test can also indicate whether the infection is caused by a type of plasmodium that is resistant to certain drugs, and whether the infection has caused any significant damage or complications. Thus, following the evaluation of the symptoms and travel history of the patient, the test should be performed without delay to determine the right treatment and ensure the quickest recovery.
The name of the abovementioned testing strategy is known as rapid antigen testing. Rapid antigen tests (RAT) are quick point-of-care (POC) diagnostic methods that are frequently employed to identify the presence of a virus of interest’s viral antigen. These lateral flow immunoassay tools can detect a viral infection a few days after the initial virus exposure or before symptoms appear. Compared to enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) tests, rapid antigen test kits offer the advantages of requiring less time, money, and laboratory equipment.
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How is Malaria treated?
It is essential to start medical treatment as soon as possible after diagnosis. The treatment of malaria typically involves the use of one or multiple anti-malarial drugs. The type and duration of treatment may depend on factors such as the type of parasite responsible for the infection, disease severity, along with the age and overall health status of the patient. Cloroquine is one of the most common drugs for the treatment of malaria. However, as certain types of malaria parasites have gained resistance against cloroquine, artemisinin-based combination therapies (ACTs) are prescribed for the treatment of some cases of malaria. If these options are unavailable, anti-malarial drugs such as quinine or doxycycline may be utilized. For infections with certain types of malaria parasites, additional drugs may also be prescribed to prevent relapses.
For now, the only approved vaccine for malaria is the RTS, S vaccine branded under the name Mosquirix, which has proved to reduce the risk of malaria by 40% in children in Ghana, Kenya, and Malawi. In 2021, the World Health Organization has recommended the use of the RTS, S vaccine for children in malaria-prone regions. Although it has not yet been peer reviewed, the pre-print study of another vaccine, the R21/Matrix-M, also demonstrates around 77% efficacy against malaria. Attempts to create more effective vaccines are ongoing with several other vaccines currently under development.
Is there a link between sickle cell trait and malaria?
It has been discovered that people with sickle cell trait (SCT) are not as affected by malaria as those with normal red blood cells. Indeed, people with sickle cell trait were observed to have lower rates of hospital admissions, severe disease, blood transfusions, bacteremia, and death linked to malaria. Throughout the course of the infection, people with sickle cell trait were observed to have 50 to 90 percent fewer parasites in their blood, and they have proved to get rid of these parasites more quickly than those with normal hemoglobin.
Although the exact reason underlying this protection is not yet determined, it is likely that multiple factors characterizing sickle cell trait contribute to the observed protection against malaria. First, the sickle cell trait may cause the destruction of red blood cells before the plasmodium completes its cycle. Sickle cell trait may also cause low concentrations of oxygen in red blood cells which may curtail parasite growth. Sickle cell trait may undermine the development of malaria by interfering with the ability of the parasite infected hemoglobin to stick to the walls of blood vessels. For more information on the connection between sickle cell trait and malaria, you can check our blog post on sickle cell disease.
What are some of the efforts for raising awareness for Malaria?
Efforts for the development of more effective treatment and vaccination for malaria are among the most important research projects for public health. Global health authorities such as World Health Organization (WHO) and Centers for Disease Control and Prevention assist in scientific research, diagnostics, epidemiological surveillance, risk assessment, monitoring, and policy development against malaria. Altogether, many global, national, and local authorities are taking initiative to encourage the adoption of evidence-based standards, policies, strategies and guidelines for the prevention and treatment of malaria. Further, World Health Organization (WHO) celebrates World Malaria Day each year on 25 April to highlight the global commitment to overcome the challenge of malaria.
- Hay, S. I., Guerra, C. A., Tatem, A. J., Noor, A. M., & Snow, R. W. (2004). The global distribution and population at risk of malaria: past, present, and future. The Lancet Infectious Diseases, 4(6), 327–336. https://doi.org/10.1016/s1473-3099(04)01043-6