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Vaccine against Lassa fever shows promise

Researchers developed a vaccine against Lassa fever that fully protects nonhuman primates from experimental infection with lethal doses of Lassa virus.

The research, published in the journal PLoS Medicine, could eventually lead to development of a vaccine for human use.

Currently there is no preventive measure available to halt the spread of Lassa fever, other than rodent control in affected areas. The disease is transmitted to humans from rodents that carry the virus.

Lassa fever is common in parts of West Africa where it causes a significant amount of death and disability among the population.
Recently, Lassa fever has been imported by travelers to the United States and Europe.
The Lassa virus that causes the disease is considered a potential agent of bioterrorism.

Principal investigators Thomas Geisbert of the U.S. Army Medical Research Institute of Infectious Diseases ( USAMRIID ) and Heinz Feldmann and Steven Jones of the Public Health Agency of Canada ( PHAC ) developed the vaccine using a non-pathogenic form of vesicular stomatitis virus, or VSV, as a carrier--into which they inserted genetic material from the deadly Lassa virus.

The team then immunized four rhesus macaques with a single dose of the Lassa vaccine, while two monkeys received only the VSV "carrier" virus.

Four weeks later, all six animals were experimentally infected with a lethal dose of Lassa virus. The four vaccinated monkeys survived with no signs of clinical illness, while the two control animals died.

" This is the first vaccine platform shown to completely protect nonhuman primates from Lassa virus," said Dr. Geisbert. " We are hopeful that the VSV strategy, which we have successfully demonstrated for Marburg, Ebola and now Lassa virus, could have utility against other hemorrhagic fevers as well."

"Lassa fever poses a huge public health threat in Western Africa," said Feldmann of the PHAC. "While the mortality rate of this virus is not as high as with some viral hemorrhagic fevers, there are many more cases of Lassa fever and a great number of survivors are permanently affected by complications such as hearing loss, so this vaccine may have a much broader application."

A vaccine against the Lassa virus could help to control outbreaks of the disease in Africa and protect health care and laboratory workers.
Previous attempts to develop Lassa vaccines were partially successful, but none completely protected nonhuman primates against lethal doses of the virus, according to the study's authors.

While these early results are promising, further testing will need to be conducted. Some issues that must be resolved before the vaccine can be tested in humans are the safety of the VSV virus, how long the vaccine protects after the shot, and whether it is active against different genetic strains of the Lassa virus.

Source: US Army Medical Research Institute of Infectious Diseases, 2005