Researchers discover how malaria parasite disperses from red blood cellsSeptember 20, 2005
The study appears in the September 20 Current Biology.
"This discovery provides the groundwork for possible new approaches to treating malaria, " said Duane Alexander, M.D., Director of the NICHD. "The malaria parasite is growing resistant to the drugs used to treat it, and new knowledge is essential for developing strategies to protect against the disease."
The study supplants earlier theories on how the malaria parasite spreads from the red blood cells it infects.
According to the World Health Organization, malaria kills more than 1 million people a year. (The WHO fact sheet, "What is Malaria?" is available on the organization's Web site at http://mosquito.who.int/cmc_upload/0/000/015/372/RBMInfosheet_1.htm )
Malaria is caused by four species of the parasite Plasmodium, the most common and deadly of which is Plasmodium falciparum. P. falciparum spends part of its life cycle in the salivary glands of mosquitoes and is transmitted to human beings through the bite of infected mosquitoes. The parasite infects red blood cells. Called a merozoite at the stage of its life when it infects red blood cells, the parasite multiplies inside the cell, until the cell ruptures and releases them. The newly released merozoites infect still other cells, and the process begins again.
To conduct the study, the researchers stained red blood cells infected with P. falciparum with two kinds of dye, explained the study's senior author, Joshua Zimmerberg, M.D., Ph.D., Chief of NICHD's Laboratory of Cellular and Molecular Biophysics. One dye stained the blood cells green, the other stained the parasites red.
In the first stage of the merozoites' release, which the researchers dubbed the "irregular schizont" stage, the red blood cell resembles a lop-sided fried egg, with the parasites visible as a sphere near the center of the cell. (A diagram of the entire sequence appears at http://www.nichd.nih.gov/new/releases/malaria_graphic.cfm ) The cell's lop-sided appearance probably results from destruction of the cytoskeleton, the molecular scaffolding that helps the cell to maintain its rounded shape.
In the next stage, called the "flower" stage, the red blood cell assumes a roughly spherical shape, covered with rounded structures that resemble the petals of a flower. Shortly thereafter, the blood cell's membrane appears to break apart. At roughly the same time, cellular compartments, called vacuoles, which encase the newly formed merozoites, also break apart. The entire process has an explosive appearance, dispersing the merozoites some distance from the cell.
During the release, Dr. Zimmerberg explained, the cell membrane appears to collapse inward upon itself and fragment into pieces.
One previous theory held that the red blood cells and the merozoite-containing vacuoles inside them swelled and then burst like a balloon containing too much air.
"The swelling was an artifact of too much light from the microscope," Dr. Zimmerberg said. "The cell membrane was light sensitive. When we turned the light down, we didn't see the swelling." Rather, he said, upon release of the merozoites, the cell membrane appeared to contract in upon itself.
Another theory held that the merozoite-containing vacuoles would fuse with the cell membrane, and then release their contents.
"But we didn't see any fusion," Dr. Zimmerberg said.
The third theory held that the cell membrane ruptured, expelling merozoite-containing vacuoles. Again, however, the researchers observed that this theory also offered an inaccurate picture, as the vacuoles ruptured at roughly the same time as the cell membrane.
Each step in the release process is a potential avenue for new therapies to treat the disease, Dr. Zimmerberg said. By first understanding how the parasite brings about these steps, it may be possible to find ways to prevent them from occurring.
NIH/National Institute of Child Health and Human D
Related Malaria Parasite Current Events and Malaria Parasite News Articles
The hidden burden of dengue fever in West Africa
Misdiagnosis of febrile illnesses as malaria is a continuing problem in Africa. A new study shows that in Ghana, dengue fever is circulating in urban areas and going undiagnosed.
Malaria plays hide-and-seek with immune system by using long noncoding RNA to switch genes
Up to one million people -- mainly pregnant woman and young children -- are killed each year by the Plasmodium falciparum parasite, which causes the most devastating form of human malaria.
Children who get vitamin A may be less likely to develop malaria
Children under age 5 living in sub-Saharan Africa were 54 percent less likely to develop malaria if they had been given a single large dose of vitamin A, new research led by the Johns Hopkins Bloomberg School of Public Health suggests.
Genetics underpinning antimalarial drug resistance revealed
The largest genome-wide association study to date of the malaria parasite Plasmodium falciparum unveils a complex genetic architecture that enables the parasite to develop resistance to our most effective antimalarial drug, artemisinin.
Hybrid 'super mosquito' resistant to insecticide-treated bed nets
Interbreeding of two malaria mosquito species in the West African country of Mali has resulted in a "super mosquito" hybrid that's resistant to insecticide-treated bed nets.
Latest research by NTU discovers reasons for malaria's drug resistance
Scientists from Nanyang Technological University (NTU) have discovered exactly how the malaria parasite is developing resistance towards the most important front-line drugs used to treat the disease.
Analogues of a natural product are drug candidates against malaria
Researchers at IRB Barcelona identify a family of efficient and selective molecules to combat the parasite Plasmodium, causal agent of malaria.
Nanotechnology Against Malaria Parasites
Malaria parasites invade human red blood cells, they then disrupt them and infect others. Researchers at the University of Basel and the Swiss Tropical and Public Health Institute have now developed so-called nanomimics of host cell membranes that trick the parasites.
Promising compound rapidly eliminates malaria parasite
An international research collaborative has determined that a promising anti-malarial compound tricks the immune system to rapidly destroy red blood cells infected with the malaria parasite but leave healthy cells unharmed. St. Jude Children's Research Hospital scientists led the study, which appears in the current online early edition of the Proceedings of the National Academy of Sciences (PNAS).
Mosquitoes and malaria: Scientists pinpoint how biting cousins have grown apart
Certain species of mosquitoes are genetically better at transmitting malaria than even some of their close cousins, according to a multi-institutional team of researchers including Virginia Tech scientists.
More Malaria Parasite Current Events and Malaria Parasite News Articles