July 29, 2009 |
Would you believe that the magic bullet against malaria is a mosquito bite? That is exactly what researchers at Radboud University in the Netherlands have demonstrated.
The vaccine group, which was exposed to bites of mosquitoes infected with the malarial parasite Plasmodium falcipurum developed immunity to malaria, while the control group, which was exposed to mosquitoes without the parasite did not. This is a breakthrough discovery since a licensed vaccine against malaria is as yet unavailable, and natural immunity to the disease develops slowly, usually after several infections.
Several decades ago, a vaccine developed with radiation-attenuated sporozoites was made, but unfortunately, in order to develop immunity by this method, a person has to sit through one thousand mosquito bites in five sessions.
This method of acquiring immunity to malaria by using intact sporozoite while simultaneously administering the anti-malarial drug chloroquine has been shown in rodents before. When a mosquito bites, it transmits the parasites which first travel to the liver where they mature and multiply; they then enter the blood stream where they invade red blood cells and continue with their asexual phase, causing the sickness associated with malaria. Chloroquine kills parasites in the asexual blood stage but the plasmodia are resistant to the drug in the pre-erythrocytic stage.
The researchers believe that the success of this method of intact sporozoites over the irradiated sporozoite model is owing to the fact that in the former case, the system is exposed to a more comprehensive array of antigens. Intact sporozoites develop into mature blood-stage parasites as opposed to the irradiated ones, which stop short of full development at the liver stage of the parasite’s life cycle. While the residual chloroquine may have extended protection in the subjects, there was no noticeable effect in the control subjects.
While this is an extremely preliminary stage in the studies, we can hope that whole-parasite vaccine strategies warrant consideration for further malaria research.