Ebola virus vaccine protects guinea pigs.

Few diseases have as fearsome a reputation as Ebola fever. Just to handle the Ebola virus, scientists must wear space suits and employ the strictest biohazard precautions. This rare illness is transmitted by close contact and most often kills humans swiftly. There is no effective treatment for Ebola fever and, so far, no way to prevent it.

In their efforts to make an Ebola vaccine, scientists have tried traditional methods--such as using an inactivated virus or a slightly modified version of a live Ebola virus--with some success in laboratory animals. These approaches can make researchers uneasy, however.

"I don't know that I'd be willing to take an injection of a purified, inactivated strain" of Ebola, says Anthony Sanchez, a virologist at the federal Centers for Disease Control and Prevention (CDC) in Atlanta. "And we can't predict what an attenuated live virus would do in a person."

Instead, Sanchez and other researchers are exploring the nascent field of gene vaccination in hopes of producing a risk-free inoculation that will protect against the Ebola virus. By injecting the genes that normally encode some of the virus' proteins, researchers at the University of Michigan Medical Center in Ann Arbor and the CDC have rendered 15 of 16 guinea pigs impervious to the Ebola virus when exposed to it less than 2 months later. Six unvaccinated guinea pigs died.

Of 10 guinea pigs exposed to the live virus 4 months after inoculation, 7 survived; all of the unvaccinated animals died. The team's findings appear in the January Nature Medicine.

Although the intact Ebola virus seems to thwart the body's immune and inflammatory mechanisms when it infects a person, the treated guinea pigs produced antibodies and T cells to battle The virus, says molecular virologist and study coauthor Gary J. Nabel of the Howard Hughes Medical Institute at the University of Michigan.

An Army research team has used a slightly different technique to prevent Ebola fever and Marburg fever, a related disease, in mice and guinea pigs. In one promising series of experiments, the researchers generated a self-replicating RNA molecule from a modified Venezuelan equine encephalitis virus and used it to carry an Ebola or Marburg virus gene that encodes a glycoprotein.

Injected into a guinea pig or mouse, this vaccine stimulates an immune response against the Ebola or Marburg virus and protects the animal. The researchers, from the U.S. Army Medical Research Institute for Infectious Diseases (USAMRIID) in Frederick, Md., describe their technique in the Dec. 22, 1997 Virology.

This week, the group began testing the technique on 12 cynomolgus macaque monkeys, the first study of primates that has used an Ebola gene vaccine. Similar research on the Marburg virus in monkeys is already under way at USAMRIID, says Jonathan E Smith, a virologist at the institute. "The real crunch issue is primate testing," Smith says. "This is crucial."

The Marburg virus was first identified in Marburg, Germany, in 1967. Ebola fever emerged near the Ebola River in the Congo, then Zaire, in 1976. Since then, researchers have identified other Ebola strains, but the Zairian virus remains the most deadly for humans, causing high fever and sometimes bleeding from every orifice.

In various outbreaks, Ebola fever has killed 50 to 90 percent of its victims. In a 1995 outbreak in Kikwit, Zaire, more than 280 people died; a spate of cases a year later in Gabon killed 43.

Because of safety protocols governing work with the Ebola virus, researchers have proceeded cautiously. For example, the protocols limit how many animals may be used, and extreme care must be taken in laboratories to avoid needle sticks or animal bites.

Some scientists are studying antiviral medications in hopes of treating Ebola victims. "Ideally, you have a vaccine and therapy," says James M. Meegan, a virologist at the National Institute of Allergy and Infectious Diseases in Bethesda, Md. "If you're the person in the [space] suit, you'd like both of those."