New Strategies in the Battle Against Malaria
Chemical-Resistant Parasite and Mosquitoes Force Change in Tactics
Jun 22, 2009
Malaria is caused by a blood-borne protozoan parasite called Plasmodium. Usually, people get malaria by being bitten by an infective female Anopheles mosquito. Only Anopheles mosquitoes can transmit malaria and they must have been infected through a previous blood meal taken on an infected person. When a mosquito bites an infected person, a small amount of blood is taken in which contains microscopic malaria parasites. About one week later, when the mosquito takes its next blood meal, these parasites mix with the mosquito's saliva and are injected into the person being bitten.
Because the Plasmodium parasite is found in red blood cells of an infected person, malaria can also be transmitted through blood transfusion, organ transplant, or the shared use of needles or syringes contaminated with blood. Malaria may also be transmitted from a mother to her unborn infant before or during delivery ("congenital" malaria).
In the human body, the parasites multiply in the liver, and then infect red blood cells. Symptoms of malaria include fever, headache, and vomiting, and usually appear between 10 and 15 days after the mosquito bite. If not treated, malaria can quickly become life-threatening by disrupting the blood supply to vital organs.
The World Health Organization estimates that each year 300 to 500 million cases of malaria occur and more than a million people die of malaria, especially in developing countries. Most deaths occur in young children. For example, in Africa, a child dies from malaria every 30 seconds. About 1,300 cases of malaria are diagnosed in the United States each year. The vast majority of cases in the United States are travelers and immigrants returning from malaria – risk areas.
Malaria is not only a serious medical problem for the individual who contracts the disease; it is also a serious economic and societal issue. Because malaria causes so much illness and death, the disease is a great drain on many national economies. Since many countries with malaria are already among the poorer nations, the disease maintains a vicious cycle of disease and poverty in those nations.
Current Malaria Treatments are not Completely Effective
The current arsenal of weapons used in the battle against malaria include pesticides to kill the mosquitoes and prescription drugs to kill the Plasmodium parasite in the body. However, as antimalaria crusader Bill Gates explains, “The parasite evolves and the mosquito evolves, so every tool we’ve ever had in the past has eventually become ineffective.”
The evolution of resistance has resulted in a multimillion-dollar treadmill of new drugs and pesticides continually being developed to replace the older and ever-increasingly ineffective older ones.
One New Approach Targets Older Mosquitoes
As Pennsylvania State University evolutionary biologist Andrew Read laments, “The harder we squeeze the parasite and mosquito, the more they’re going to evolve and respond.”
In an effort to end this cycle, Read has developed a new approach to using pesticides to kill the mosquitoes that carry the parasite. He is targeting older mosquitoes because older mosquitoes nearing the end of their reproductive lives are also the most likely to be disease carriers. Targeting older mosquitoes could be as simple as applying fungal biopesticides that kill mosquitoes up to two weeks after contact, when a large portion of the insect’s short lifespan has passed. Allowing younger mosquitoes to continue reproducing reduces the development of resistance which in turn keeps infection rates low.
Another New Approach Alters Red Blood Cells
Another new approach focuses on the Plasmodium parasite and its interaction with red blood cells. The parasite first multiplies in the liver and then moves out into the blood stream where it enters and devours the inner content of one red blood cell after another.
Traditionally, researchers have focused on keeping the parasite from entering the cells in the first place. But now University of Pennsylvania biochemist Doron Greenbaum has found a way to lock the parasite inside red blood cells once it enters. By blocking the action of key host protein called calpain, the parasite is unable to escape the red blood cell once inside. Greenbaum believes it might be more difficult for the Plasmodium parasite to evolve resistance to a drug aimed at a host protein rather than one aimed directly at the parasite itself.
In the evolutionary arms race that has become the battle against malaria, subtle flanking maneuvers such as these new approaches may ultimately prove most effective.
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