Malaria is a parasitic disease spread by mosquitoes that causes an estimated 1 million deaths per year. Four different types of Plasmodium parasites can cause malaria and in many regions of the world these parasites have developed resistance to a variety of the medicines used to treat malaria. It is believed that the development of a vaccine will be the most effective way to decrease the amount of deaths caused by this disease. In the past, vaccine development for malaria focused on inducing antibodies that are able to recognize antigens found on the surface of the parasites. However, this type of vaccine has so far been unsuccessful due to the numerous polymorphisms found in the proteins that make up the surface of the parasites, These polymorphisms enable the parasites to evade the host's immune system. In the past ten years, different methods have been used to research the effects of infecting rodents with low-density blood-stage infections of the Plasmodium parasites to induce immunity.
In a recent study led by Michael Good at the Institute for Glycomics at Griffith University in Queensland, Australia, vaccination with chemically attenuated parasites led to the induction of immunity to different malaria parasite species in in rodents. The study found that parasites treated with a chemical that irreversibly alkylated their DNA, making it difficult for them to replicate, were able to induce immunity in a variety of species of mice. The efficacy of the vaccine was dependent on the membrane of the red blood cells, infected with merozoites from the parasite, remaining intact. These intact red blood cell membranes were able to act as a target to the antigen-presenting cells of the host and enabled the host's immune system to recognize the potential threat of the infected cells. The host's immune system was able to create antibodies to fight off these cells along with memory cells that were able to effectively fight off a non-attenuated infection of malaria. This type of immunity is therefore dependent upon a mechanism that uses CD4<sup>+</sup>T cells. Further research is needed to prove that vaccination with attenuated parasites will not alter the tissue structure of the liver of the host along with disproving concerns that vaccination with attenuated parasites may lead to a more dangerous phenotype of parasite within the host.