How Is Malaria Detected?
As a serious and potentially life-threatening disease that is still affecting millions of people around the world, the prompt and accurate diagnosis of malaria remains critical for the reduction of disease transmission and the prevention of associated mortality or morbidity. With the introduction of novel diagnostic devices utilizing different methods, diagnostic solutions for malaria have become more accessible and flexible all around the world. However, as different testing options offer varying advantages depending on the epidemiology of infection, level of access to testing, and regional strategies of control, each of the different diagnostic options for malaria has utmost importance for public health purposes and clinical studies. Read along to learn more about malaria, its modes of transmission, life cycle, symptoms, and diagnosis.
What causes malaria?
Malaria is caused by protozoan parasites of the genus Plasmodium, belonging to the phylum Apicomplexa. Although more than 200 species of the genus Plasmodium have been discovered to infect reptiles, birds, and mammals, so far, there are only five species of Plasmodium that is known to affect humans: Plasmodium falciparum (P. Falciparum), Plasmodium malariae (P. malariae), Plasmodium vivax (P. vivax), Plasmodium ovale (P. ovale), and Plasmodium knowlesi (P. knowlesi). Malaria is transmitted among humans through the bite of female mosquitoes of the genus Anopheles. Once the parasites enter the human body, they travel to and grow within a vertebrate body tissue, typically the liver. After they mature, the parasites return to the bloodstream, infect red blood cells, and multiply until the host cells rupture. The rupture of the host red blood cells, in turn, releases more parasites into the bloodstream of the infected person. Some species of plasmodium can lay dormant within the liver stage for several months and even years. However, once the parasites enter the bloodstream, the infection of healthy blood cells and their ensuing destruction can lead to the development of symptoms.
How common is malaria?
Although malaria is mostly wiped out in many parts of the world including the United States and Europe, it remains relatively common in Africa, South and Southeast Asia, Central and South America, the Middle East, and Oceania. In 2020, there were more than 241 million reported cases of malaria worldwide, with 627,000 deaths. Most of these cases were reported from Africa and South Asia, with the majority deaths occurring in children.
How does malaria transmit?
Malaria cannot spread directly from person to person. The main mode of transmission of malaria is through bites from infected Anopheles mosquitoes that have previously had a blood meal from a person with parasitemia. As an infected mosquito bites a person, the parasites on their infective form, called sporozoites, are transferred from its salivary glands into the bloodstream. Sporozoites travel to liver cells where they undergo asexual multiplication called schizogony, and lead to the formation of merozoites. Following maturation, the merozoites leave the liver cells and disperse into red blood cells within the bloodstream. Within the cytoplasm of red blood cells, merozoites digest hemoglobin, grow, and develop into a round form called trophozoites. Like the liver stage, trophozoites undergo schizogony and further cellular differentiation leads to the formation of merozoites. Once the host red blood cell ruptures, the merozoites are released into the bloodstream to further infect healthy red blood cells. Some merozoites develop into male and female gametocytes, which are transferred to an Anopheles mosquito during its next blood meal. After undergoing gametogenesis in the body of the mosquito, gametocytes form gametes and microgametes and produce a zygote. The zygote develops into an oocyst and ruptures to release hundreds of sporozoites. These sporozoites eventually reach the salivary glands of the mosquito to restart the life cycle of the parasite. While the main route of transmission of malaria is through Anopheles mosquitoes, the infection has also been reported to transmit vertically from an infected mother to her child, and spread via organ transplants, blood transfusions, or shared needles.
What are the signs and symptoms of malaria?
The incubation period between the time of infection and the onset of symptoms usually varies between 7 to 30 days. However, with infections caused by certain species of plasmodium or preventive medicine use, symptoms may not appear for several months following exposure. Further, people with histories of previous malaria infections may develop few or no symptoms. The early stage of malaria is characterized by flu-like symptoms such as fever, chills, sweating, headache, nausea, vomiting, diarrhea, body aches, and fatigue. Episodes of fever and other symptoms may appear, disappear, and follow each other in a cyclical manner.
Symptoms and disease severity may depend on the age and health status of the patient, along with the type of plasmodium causing the infection. While infections with P. vivax and P. ovale typically cause less severe disease which can remain dormant in the liver for many months, P. malaria may lead to serious disease and potentially life-threatening complications. Severe cases of malaria can result in the impairment of brain function and spinal cord, loss of consciousness, seizures, liver and kidney failure, coma, and death.
How is malaria diagnosed?
Malaria can be diagnosed via microscopy, polymerase chain reaction (PCR), and rapid diagnostic tests (RDTs). Although a single test may not inform on all these concerns, these diagnostic tools not only enable the detection of the parasite in the blood, but also determine the type of Plasmodium causing the infection, and whether it is leading to serious complications. As such, these tests provide ample information on drug resistance, health status, and infection severity, which are critical for the implementation of proper treatment.
The diagnosis of malaria through the microscopy method involves the examination of a blood smear collected from the patient with a light microscope. This microscopic examination and visualization allow for the detection of the infection and differentiation of the parasite among other species of Plasmodium. On the other hand, polymerase chain reaction (PCR) tests offer a molecular method for the detection of Plasmodium DNA in peripheral blood samples.
Finally, rapid antigen tests (RDTs) utilize dye-labelled antibodies which capture specific antigens produced by Plasmodium to detect malaria infections in blood samples. If Plasmodium antigens are present in the sample, the labeled antibodies bind to the parasite antigens to form antigen-antibody complexes. As these complexes travel on the membrane by capillary flow, they are captured by a line of bound antibodies, which leads to the formation of a colored line in the results window. Some RDTs can only detect one species of Plasmodium, whereas other devices, such as our RapidFor™ Malaria P.F./Pan Rapid Test Kit, RapidFor™ Malaria P.F./P.V Rapid Test Kit and RapidFor™ Malaria P.F. Rapid Test Kit, can detect and differentiate among multiple species. Although light microscopy of thick or thin stained blood smears remains the standard method for diagnosing malaria, RDTs offer an alternative to microscopic or molecular tests especially where access to high-quality microscopy or laboratory services may be limited.