Researchers say they have evidence the malaria parasite lurks in bone marrow, a spongy tissue inside bones where blood cells are produced. The discovery offers hope that new treatments can be found to fight the disease, which kills an estimated one million people each year.
The malaria parasite goes through a number of stages in its life cycle. After an infected mosquito bites someone, parasitic spores travel to the liver where they grow and divide. Then they enter the blood stream and multiply, causing the familiar symptoms of malaria - high fever, chills, sweats, fatigue, nausea and vomiting.
But there appears to be another place where immature malaria spores gather and hide - bone marrow. And once there, they can evade the body's defenses as they develop.
For about 100 years, researchers have suspected a small amount of the pathogen, called Plasmodium falciparum, burrows deep inside bones.
“It was assumed that all of the blood stages of the parasite are somehow sticking to the blood vessels. But these guys are not. They are outside of the blood vessels. They are in the hematopoietic system where blood is formed. So drugs have to get there first," said Matt Marti, who specializes in malaria transmission at Harvard School of Public Health in Boston, Massachusetts.
But drugs have a hard time penetrating to the bone marrow, says Marti, which may explain why malaria - out of easy reach of the immune system - is difficult to treat.
Investigators discovered the new reservoir of P. falciparum by studying the bone marrow of people who died of malaria.
Marti says the findings may help scientists find ways to target those reservoirs during a critical stage of the parasite's life cycle.
“So, it will be important to figure out whether current anti-malarial therapies are efficiently targeting that site. And it will be important for new drugs to be tested - whether they can target that site efficiently," he said.
Researchers report on the role of bone marrow in malaria infection in Science Translational Medicine.