for National Geographic News
Scientists have genetically engineered tomato and tobacco plants to produce a vaccine against the virus that causes severe acute respiratory syndrome, or SARS, the disease that killed nearly 800 people in 2003.
Meanwhile, another team of researchers has developed a vaccine that protects monkeys against the deadly Ebola and Marburg viruses, which have plagued central Africa. An ongoing Marburg outbreak in Angola has killed at least 357 people.
While both vaccines are far from ready for human use, the studies raise the possibility of producing economical vaccines for diseases for which there is no known cure.
"There was a need to prepare quickly a vaccine that is inexpensive and safe," said Hilary Koprowski, who is the director of the Center for Neurovirology at Jefferson Medical College in Philadelphia, Pennsylvania.
Koprowski, who produced the first oral polio vaccine and developed the rabies vaccine, is the lead researcher on the SARS vaccine study, which is published today in the Proceedings of the National Academy of Sciences, a science journal.
The Ebola and Marburg research was published last week in the academic journal Nature Medicine.
One reason it is difficult to develop vaccines for diseases like SARS and Ebola is because some viruses are believed to mutate constantly. If a virus changes quickly, a vaccine might be suitable for a while but not forever.
The SARS, Ebola, and Marburg viruses all have RNA genomes, notes Doris Bucher, an associate professor in the Department of Microbiology and Immunology at New York Medical College in Valhalla.
RNA is chemical similar in structure to DNA that plays an important role in the chemical activities of cells.
"RNA viruses are subject to a great deal of antigenic variation"changes that evade the defense mechanisms of host species"due to the high mutability of the RNA genome as a result of errors in transcription [reproduction] of the genome," Bucher said.
"Two viruses with RNA genomes, influenza virus and HIV, are especially notorious for their antigenic variation [which] requires the re-formulation of the influenza vaccine on a near annual basis," she added. Bucher notes that the development of an HIV vaccine has been similarly challenged.
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