July 16, 2018Tropical Disease
Malaria is a mosquito-borne infectious disease affecting humans and other animals caused by parasitic protozoans (a group of single-celled microorganisms) belonging to the Plasmodium type. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases it can cause yellow skin, seizures, coma, or death. Symptoms usually begin ten to fifteen days after being bitten. If not properly treated, people may have recurrences of the disease months later. In those who have recently survived an infection, reinfection usually causes milder symptoms. This partial resistance disappears over months to years if the person has no continuing exposure to malaria.
The disease is most commonly transmitted by an infected female Anopheles mosquito. The mosquito bite introduces the parasites from the mosquito's saliva into a person's blood. The parasites travel to the liver where they mature and reproduce. Five species of Plasmodium can infect and be spread by humans. Most deaths are caused by P. falciparum because P. vivax, P. ovale, and P. malariae, generally cause a milder form of malaria. The species P. knowlesi rarely causes disease in humans. Malaria is typically diagnosed by the microscopic examination of blood using blood films, or with antigen-based rapid diagnostic tests. Methods that use the polymerase chain reaction to detect the parasite's DNA have been developed, but are not widely used in areas where malaria is common due to their cost and complexity.
During a malarial infection, the vacuole, which is a compartment inside human red blood cells in which malaria parasites reproduce and develop, takes on a distinct spherical shape just minutes before its membrane ruptures, which leads to the release of parasites into the blood stream. According to an article published in Cellular Microbiology (11 July 2018), while working with red blood cells from healthy donors, the authors were able to chemically block the sequence of events leading to this rounding of the vacuole. To track the rounding sequence under a microscope, the authors dyed the membrane of the vacuole with a substance that gives off green light. About 10 minutes before the membrane ruptured, the vacuole morphed from a lumpy, uneven shape to a sphere. Previous studies have shown that malaria parasites use calcium to trigger the biochemical reactions needed for their release from the cell. When the authors treated the cells with a compound that blocks calcium's effect, the vacuoles couldn't transition to the spherical form, trapping the parasites inside the cell.
The authors noted that targeting this sequence could inform new treatment strategies against Plasmodium falciparum, the species of malaria parasite that causes the most deaths worldwide and, in several areas, has become drug-resistant.