Ebola Vaccine Candidate

By Sean Henahan, Access Excellence

Graphic: Electron Micrograph of Ebola Virus (Courtesy Dr. FA Murphy)

Attempts to provide immunization against Ebola virus with conventional vaccine technologies have not been successful. Now, a research team from the Howard Hughes Medical Institute has developed what appears to be  the first effective vaccination against the Ebola virus. The team immunized guinea-pigs against Ebola by intramuscular injection of a DNA vaccine made up of plasmids containing Ebola virus proteins. The animals were protected from infection when challenged with the virus two and four months after immunization.

After earlier research suggested that the immune response to Ebola could be triggered by exposure to proteins on the outer envelop of the virus, the researchers isolated the genes responsible for those proteins and inserted them into circular bacteria called plasmids. After injection into muscle, the plasmid vector carried the recombinant virus proteins into the animals cells. When the guinea pig cells began to express the related protein, the immune system of the animals kicked in with antibody and T-cell based immune responses sufficient to stop the virus.

Ebola virus infection is fatal in a majority of cases, subjecting its victims to a horrible hemorrhagic disease which kills them in a matter of days. The natural reservoir of the virus remains unknown, as do the specifics of pathogenesis of the infection. The virus has a very specific tropism for liver cells and cells of the reticuloendothelial system, e.g. macrophages. Massive destruction of the liver is a hallmark feature of the disease. Researchers have also noted that people killed by the virus have not had the time to mount an immune response.

Ebola virus infection is rare, with only about 1,000 cases reported in a handful of outbreaks, most in central Africa. The virus gained notoriety after an outbreak in Zaire in 1995 killed 244 people. Further attention came with the publication of 'The Hot Zone', a book by Richard Preston describing outbreaks of Ebola in Africa and a near outbreak in suburban Virginia. "Outbreak" , a film starring Dustin Hoffman, added to the public hysteria.

Although Ebola infection is rare, public health officials are very concerned about the potential for the disease to become an international epidemic. The virus can be readily transmitted by close physical contact.

"Major changes in urbanization, fluctuation in socioeconomic structures and the speed of travel, now more than ever, allow these viruses to present a serious threat to world public health," notes Dr. Thomas Folks, of the Retroviruses Disease Branch of the CDC.

The new Ebola vaccine candidate is an example of  genetic immunization. The current research is only the first step towards developing a vaccine that might be used in humans. The researchers hope to test the vaccine in nonhuman primates within 12 months. Researchers are also using this method to develop vaccines against other infectious diseases including influenza, malaria and tuberculosis.
 
 The research appears in the January 1998 issue of Nature Medicine. 

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