A new study, published by a team from the Center for Infectious Disease Research in Seattle, suggests that disabling just three of the malaria parasite’s genes could create a safe and effective vaccine against the infectious disease. So far, no vaccine of this nature has become available for the disease, which affects almost 200 million people annually, according to one recent study. The team was led by parasitologist Stefan Kappe.
Plasmodia are microscopic parasites that infect both an insect host and a vertebrate host in their lifetime, often first infecting a mosquito host that transfers the parasite to a human. Once under the skin, the parasites move on to the liver to reproduce, and into the blood stream to infect red blood cells. This can lead to further problems, proving fatal in some cases. The multi-stage infection has made it especially challenging to create a vaccine. One vaccine, called RTS,S, uses an engineered version of a protein from the most problematic strain of the parasite, to help the immune system learn to fight the plasmodia. It has yet to become available, set to hit the market in Africa in 2018. Another approach uses radiation to damage the parasite’s sporozoites, stopping them from reproducing. RTS,S is the favored approach, and even that only protected between 27 and 39 percent of infants in large scale studies.
The new approach to creating a vaccine affects just 3 genes that the parasites uses to progress into the human blood stream. The team infected mice with this “genetically attenuated parasite” (GAP). When the mice were later infected with the unmodified version, the study demonstrated that they were protected from the disease. The team then infected mosquitos with a GAP designed for the deadliest strain of plasmodium in humans, putting those mosquitos on the arms of 10 human volunteers. Their study, published in Science Translational Medicine, showed that not one of the volunteers developed Malaria or other problems during these initial tests. The vaccine successfully triggered an immune response against the parasite’s sporozites.
Since the current favorite approach to a vaccine, RTS,S, has drawbacks such as the need for booster doses over time, and mediocre effectiveness, the new approach could become the favored method for such a vaccine.
Robert Seder, an immunologist at the U.S. National Institute of Allergy and Infectious Diseases, said that the method “holds great promise.”
However, with only early, small scale trials completed, there will be a long road ahead to prove the safety and efficacy of such a vaccine.