Malaria vaccines: the failed promise

Article Abstract:

Despite early optimism, prospects for an effective vaccine against malaria seem as remote as ever. Researchers have examined the three-stage life cycle of the malaria parasite, plasmodium, looking for the best place to attack. The sporozoite is injected by the mosquito as it bites; it gets carried to the liver where thousands of merozoites are produced. Each merozoite invades a red blood cell, where it continues to multiply, ultimately causing the red cell to burst. Waves of bursting red blood cells are responsible for the symptoms of malaria. Occasionally, a merozoite stops replicating and becomes a gametocyte, which may be eaten by mosquitoes in the completion of the host cycle. Unfortunately, attempts to protect people against malaria by immunization with sporozoite and merozoite antigens have failed; not only are these stages present outside of blood cells for only a fleeting moment, but their antigens are surprisingly variable as well. Vaccines can be made, but they simply do not protect against a rapidly changing enemy. Some researchers favor a vaccine against the gametocyte, which they feel should be less immunologically variable. Perhaps ironically, such a vaccine would not prevent recipients from getting malaria; it would only prevent them from transmitting their disease back to more mosquitoes. Though serious problems remain to be solved, and researchers are more hesitant than ever to make optimistic predictions, the potential benefits to world health are great enough to ensure that the search for a malaria vaccine will continue. (Consumer Summary produced by Reliance Medical Information, Inc.)

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Circumsporozoite protein heterogeneity in the human malaria parasite Plasmodium vivax

Article Abstract:

Malaria, a disease caused by the parasite Plasmodium, results in the destruction of red blood cells, which can lead to death. Plasmodium vivax is one of the four species of Plasmodium which causes the disease in humans. Because of the severity and the widespread occurrence of the disease, especially in third world countries, researchers are trying to develop a vaccine against the malaria parasite. If molecules on the surface of the parasites are similar from one parasite to another, the body's immune system could recognize that the molecules are foreign, produce antibodies against it and destroy the parasite. This would make an individual immune to any parasite with those same identifying molecules. If the molecules are not similar, however, the immune system would not be capable of destroying the parasite. A molecule on the parasite called the circumsporozoite (CS) protein is very similar in strains of Plasmodium found in many diverse geographical locations. The CS protein is one of the major candidates for vaccine development. However, in this study, 14 percent of the parasites isolated from a province in western Thailand were not recognized by antibodies to the CS protein found in other forms of the parasite. Changes in amino acids, which comprise the protein molecules, were found in the CS protein from these isolates, compared to the conserved CS protein, found in parasites from most other geographical locations. This study shows that the CS protein is not as reliable a marker as was thought and that a vaccine against the CS protein would not provide protection against all malaria-causing parasites.

Physiological aspects, Plasmodium, Plasmodium (Protozoa)

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Malaria hideout found in new mothers

Article Abstract:

First-time mothers who had been immune to malaria often become vulnerable to the disease during pregnancy due to the susceptibility of the placental wall. Chondroitin sulfate A (CSA), a malaria-prone receptor protein produced during pregnancy, is the focus of exciting new research.

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