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U.S. Department of Health and Human Services

Vaccines, Blood & Biologics

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Sensitive test for malaria protein could help FDA better evaluate malaria vaccines and give public health workers a new tool for tracking outbreaks


Scientists at the US Food and Drug Administration (FDA) have collaborated on the development of the most sensitive and reliable laboratory technique reported to date for quantitative determination of antigenic component in malaria vaccines.  The assay, or a modified version of it, could also track malaria transmission in communities and measure how well public health measures to reduce malaria transmission have succeeded, according to the scientists.  The FDA collaboration included scientists from The Johns Hopkins Bloomberg School of Public Health and the PATH Malaria Vaccine Initiative. PATH is a nonprofit group in Seattle, WA that develops technological solutions to third world problems.
Malaria, caused by a single-celled parasite belonging to genus Plasmodium,is transmitted in areas in 106 countries risking about 3.3 billion people. Anopheles mosquitoes spread the parasite to humans through their bites; the parasite then travels to the liver, where it matures and reproduces in forms that infect the red cells and cause clinical symptoms. Typical symptoms of malaria include fever and headache, which in some individuals can progress to severe anemia, coma or death. The disease killed over 655,000 individuals worldwide in 2010.   
The new assay detects a protein on the surface of the Plasmodium parasite that is the basis of some candidate malaria vaccines under development. This protein, called Plasmodium falciparum circumsporozoite protein (PfCSP), triggers immune responses against the parasite that may protect some individuals from malaria. The assay, called a chemiluminescent-western blot assay, determines the amount of PfCSP on either of two types of vaccines: whole malaria sporozoites, or a recombinant form of PfCSP (protein made through genetically engineering an organism to manufacture it). Using antibodies, enzymes, and a special chemical solution, the assay generates tiny amounts of signal that a special detector collects and uses to determine the amount of PfCSP present in sample. The more PfCSP there is, the greater the amount of signal is released.  
The assay is extremely sensitive and reliable (i.e., repeating tests on the same sample produces very similar results): It can detect trillionths of a gram of PfCSP protein on a vaccine made from a whole parasite or recombinant PfCSP.
The extreme sensitivity and good reliability of the test suggest it could be valuable for estimating how much PfCSP is present in a candidate malaria vaccine preparation—a critical step in evaluating the quality of the vaccine and predicting whether it will be effective. However, this assay is not designed to predict the safety of malaria vaccines.  PfCSP is also expressed in malaria parasites developing inside mosquitoes, and therefore, researchers might be able to adapt the assay for monitoring and tracking of how many mosquitoes in a given area are infected, and thereby able to evaluate the success of anti-malaria public health programs in reducing the spread of the disease.
The FDA researchers are in the Office of Blood Research and Review.
“A chemiluminescent-western blot assay for quantitative detection of Plasmodium falciparum cirumsporozoite protein”
Journal of Immunological Methods; 2013 Online Feb 8
doi: 10.1016/j.jim.2013.02.001
Kumar S. Zheng H, Sangweme DT, Mahajan B, Kozakai Y, Pham PT, Morin MJ, Locke E, Kumar N
Laboratory of Emerging Pathogens, Division of Emerging and Transfusion Transmitted Diseases, Office of Blood Research and Review, Center for Biologics Evaluation and Research, Food and Drug Administration, Rockville, MD 20852