Credit: Monika Wisniewska

Filoviruses (Ebola and Marburg viruses) are highly infectious pathogens that cause hemorrhagic fever in humans and nonhuman primates. Their mortality rates approach 90% in humans. There are currently no approved vaccines against filoviruses.

New research presented at the 2008 American Society for Microbiology's Biodefense and Emerging Diseases Research Meeting in Baltimore, MD, shows that a vaccine that combines Ebola and Marburg virus-like particles (VLPs) protects macaques against the filoviruses. The work builds on previous studies using guinea pigs.

Kelly L. Warfield (United States Army Medical Research Institute of Infectious Diseases, Ft. Detrick, MD) and her colleagues previously showed that VLP-based vaccines could protect against filoviruses in guinea pigs. Given separately, the Ebola or Marburg VLPs protected guinea pigs against the corresponding filovirus, but not the other virus. Given together in a single dose, however, the Ebola and Marburg VLPs elicited strong immune responses and protected guinea pigs against both filoviruses.

Warfield's new research tested the combined Ebola and Marburg VLPs in more than 50 cynomolgus macaques. Vaccinated macaques developed strong Ebola- and Marburg-specific antibody titers and survived exposure to the filoviruses without developing clinical or laboratory signs of infection, whereas control animals succumbed to filovirus infection.

More studies are planned to determine how many doses of the vaccine are necessary and whether boosters are needed for long-term protection. In addition, investigators hope to develop a vaccine that will offer protection against all known pathogenic filovirus strains.

Traditional antiviral vaccines used whole viruses: either a virus genetically similar to the pathogen that would cause an immune response but not the disease, or the pathogen itself that had been weakened or killed in order to minimize risk of disease. These traditional vaccines carry a small risk of viral infection. Because the VLP-based vaccines do not use whole viruses, they carry no risk of infection, making them potentially safer than other antiviral vaccines. Some VLP-based vaccines are already available in the US, such as the vaccine against human papillomavirus.

Filoviruses present a potential bioterrorism threat because they are highly infectious, have high mortality rates and lack approved vaccines. The new VLP-based vaccine was safe and effective in protecting macaques against filovirus infection, making it “a leading candidate for use as a filovirus vaccine in humans,” according to Warfield. Researchers hope to begin testing the vaccine in humans in coming years.