An experimental vaccine grown in tobacco plants against deadly Ebola hemorrhagic fever protected more than 80 percent of mice given a lethal dose of the virus, and may protect humans as well, researchers said.
The vaccine, unlike previous experimental vaccines, is also stable enough to stockpile in case of bioterrorism, according to the study in the Proceedings of the National Academy of Sciences. The next step is to test it in nonhuman primates.
Ebola, first identified in 1976 in Sudan and Zaire, which is now the Democratic Republic of the Congo, is among the most lethal diseases known to humans, according to the World Health Organization. Some species of the virus cause deaths in as much as 90 percent of all people who are clinically ill. Once a human is infected, there is no cure.
“If Ebola is ever deliberately introduced as a bioterrorism agent, we would pull this out and begin using it,” said Charles Arntzen, a vaccine specialist at Arizona State University in Tempe, Arizona, and an author of the study, in a telephone interview.
The vaccine was created using a tobacco plant, by introducing a protein from the outside of the virus into the plant. The resulting product is an “immune complex,” a combination of the virus protein and an antibody, designed to spur the body’s defenses against the infection. Traditional vaccines are made from weakened or inactivated viruses.
Researchers gave the mice the vaccine along with a chemical to prompt the immune system to create more antibodies to the virus, Arntzen said.
Previous efforts at Ebola vaccines introduced the protein from the surface of the virus to other viruses, Arntzen said. Unfortunately, those vaccines decomposed over time, losing their effectiveness and making them unsuitable candidates for stockpiling.
Should the vaccine work and be approved for human use, it probably will also be used in Africa, around Ebola outbreaks, according to Arntzen.
The incubation period for Ebola is 2 to 21 days, according to the U.S. Centers for Disease Control and Prevention. Then, a patient has a fever, headache, rash, muscle aches, sore throat and weakness. That’s followed by diarrhea, vomiting, and stomach pain. Some patients have red eyes and bleed through the skin.
No case of Ebola in humans has ever been reported in the U.S., although people have been infected in the Democratic Republic of the Congo, Gabon, Sudan, the Ivory Coast, Uganda, and the Republic of the Congo.
After vaccinating the mice four times in 56 days, the animals were sent to the U.S. Army Medical Research Institute, where they kept for two weeks before being given a dose of Ebola that is usually lethal.