In recent years, public health experts have increasingly explored the idea of eliminating the most dangerous malaria-causing parasite. But they have questioned whether getting rid of this species, called Plasmodium falciparum, would allow other species of the parasite to simply jump into the gap and start infecting humans with malaria.
Now, a new study led by a researcher at the University of Maryland School of Medicine indicates it is very unlikely that Plasmodium species that infect other animals--such as apes, birds and reptiles--would cross over easily to humans. Using sophisticated genetic analysis, Joana C. Silva, PhD, found evidence showing that five other common Plasmodium species have not changed which animals they infect for at least 3 million years.
Malaria is a leading cause of disease and death throughout the world; every year it infects over 200 million people, and causes more than half a million deaths. In parts of sub-Saharan Africa and South Asia, the disease is common and causes enormous suffering and hardship.
The new study was published last month in the journal Molecular Biology and Evolution. Dr. Silva, an assistant professor in the Department of Microbiology and Immunology and at the Institute for Genome Sciences at the UM SOM, was the lead author.
"This is a key question - how likely are these parasite species to jump to humans?" says Dr. Silva. "And according to our results, "host switching" by malaria-causing parasites is not at all a common event, on an evolutionary time scale."
More than 200 Plasmodium species have been identified. Plasmodium falciparum is the most lethal of the five that are known to infect humans. Researchers are examining new approaches to reduce or eliminate Plasmodium falciparum by developing vaccines against it, for example, or spreading a bacterium that kills the mosquitoes that carry it. But some scientists have expressed concern that Plasmodium falciparum's ecological niche might be quickly filled by other Plasmodium species.
Dr. Silva and her co-authors looked at hundreds of genes spread across five different species of Plasmodium. Their goal was to discover how closely related the genes were--in effect, how long ago they had diverged from each other. If they had separated recently, it was more likely that they could jump from infecting one species to another.
To get their results, Dr. Silva and her colleagues developed a new statistical approach to determine when Plasmodium species split off from one another. The new method uses molecular data from thousands of genes; current techniques, by contrast, use at most sequences from dozens. This new approach is not only more reliable, but also faster.
"This is exciting research that has powerful public health implications," said Dean E. Albert Reece, MD, PhD, MBA, who is also the vice president for Medical Affairs, University of Maryland, and the John Z. and Akiko K. Bowers Distinguished Professor and Dean of the School of Medicine. "It is particularly interesting to see the application of 'big data' and genetic analysis increasingly being used to help solve the world's most critical health problems."
The research team included scientists and statisticians from the National Center for Biotechnology Information at the National Institutes of Health and the Applied Mathematics & Statistics, and Scientific Computation program at the University of Maryland, College Park (UMCP).
"This is an exciting integration of mathematics and genetics," said David Harris, a researcher in the UMCP Applied Mathematics & Statistics and Scientific Computation program, who developed the statistical methods used in this research. "It's great to be able to use mathematics in a way that has the potential to inform practical policy decisions."
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The research was supported by the National Institute of Allergy and Infectious Diseases (NIAID) at the National Institutes of Health, and by the Intramural Research Program of the National Library of Medicine.
About the University of Maryland School of Medicine
The University of Maryland School of Medicine was chartered in 1807 and is the first public medical school in the United States and continues today as an innovative leader in accelerating innovation and discovery in medicine. The School of Medicine is the founding school of the University of Maryland and is an integral part of the 11-campus University System of Maryland. Located on the University of Maryland's Baltimore campus, the School of Medicine works closely with the University of Maryland Medical Center and Medical System to provide a research-intensive, academic and clinically based education. With 43 academic departments, centers and institutes and a faculty of more than 3,000 physicians and research scientists plus more than $400 million in extramural funding, the School is regarded as one of the leading biomedical research institutions in the U.S. with top-tier faculty and programs in cancer, brain science, surgery and transplantation, trauma and emergency medicine, vaccine development and human genomics, among other centers of excellence. The School is not only concerned with the health of the citizens of Maryland and the nation, but also has a global presence, with research and treatment facilities in more than 35 countries around the world.
About the Institute for Genome Sciences
The Institute for Genome Sciences (IGS) is an international research center within the University of Maryland School of Medicine. Comprised of an interdisciplinary, multidepartment team of investigators, the Institute uses the powerful tools of genomics and bioinformatics to understand genome function in health and disease, to study molecular and cellular networks in a variety of model systems, and to generate data and bioinformatics resources of value to the international scientific community. http://www.igs.umaryland.edu
About the University of Maryland College of Computer, Mathematical, and Natural Sciences
The College of Computer, Mathematical, and Natural Sciences at the University of Maryland educates more than 7,000 future scientific leaders in its undergraduate and graduate programs each year. The college's 10 departments and more than a dozen interdisciplinary research centers foster scientific discovery with annual sponsored research funding exceeding $150 million.
Journal
Molecular Biology and Evolution