Scientists have come closer to developing a vaccine to one of the deadliest diseases known. In the 20 November issue of Nature, they report that a new DNA vaccine can protect macaques from developing Ebola hemorrhagic fever, the highly contagious and lethal disease that occasionally terrorizes sub-Saharan Africa.
Ebola causes devastating symptoms such as shock and internal bleeding. The virus can kill up to 90% of its victims, often within 10 days of infection. Currently, there's an epidemic in Uganda, which has so far sickened at least 337 people and killed 121. There are no drugs for Ebola, and most scientists think a vaccine would be the best way to protect populations at risk. But so far, efforts to develop such a vaccine have failed.
Now, a team of researchers from the National Institutes of Health's Vaccine Research Center in Bethesda, Maryland, and the Centers for Disease Control and Prevention in Atlanta has developed a DNA vaccine. This kind of vaccine consists of a piece of viral DNA--in this case, a stretch encoding the virus's envelope--that is injected into muscle. The hope is that the gene will be expressed as a harmless protein and will teach the immune system how to defeat the real virus.
The team vaccinated four macaque monkeys; each first received three shots with the gene in the form of a piece of "naked DNA," and several months later, a booster made of an adenovirus expressing the same gene. The vaccinated monkeys developed antibodies and immune cells against the virus; what's more, they survived an injection with the Ebola virus and were healthy many months later. Four unvaccinated monkeys that served as a control group were dead or dying within a week after the injection.
Other scientists say the results look promising, but some point out that the vaccine may have worked because the team challenged their monkeys with a relatively low dose of Ebola. "I am cautiously optimistic that [this vaccine] is a significant step forward," says virologist Alan Schmaljohn of the U.S. Army Medical Research Institute of Infections Diseases in Frederick, Maryland. "I will be more comfortable once it is repeated with a higher challenge dose."