Ebola Vaccine Candidate
By Sean Henahan, Access Excellence
Arbor, MI (12/30/97) A promising new candidate vaccine against Ebola
virus offers an entirely new genetically engineered approach to immunization.
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
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
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.