Vaccine against Lassa fever works in monkeys

Jun 28 2005

Scientists say that a genetically engineered virus may possibly offer the first effective vaccine against Lassa fever.

The vaccine apparently successfully protected four monkeys against Lassa fever, a deadly hemorrhagic fever common in West Africa.

Lassa fever causes high fever, internal bleeding and kills at least 5,000 people a year.

The virus is similar to Ebola, Marburg and yellow fever but though it is far less likely to be fatal, it is, far more common.

U.S. and Canadian scientists say that the vaccine is the first platform shown to completely protect nonhuman primates from Lassa virus.

Dr. Thomas Geisbert of the U.S. Army Medical Research Institute of Infectious Diseases in Frederick, Maryland, says they are hopeful that the VSV strategy, which they have successfully demonstrated for Marburg, Ebola and now Lassa virus, could also be useful against other hemorrhagic fevers.

The VSV vaccine is so-called for vesicular stomatitis virus, which is genetically engineered to carry some of the genetic material from the Lassa virus.

The scientists immunized four rhesus monkeys with a single dose of the Lassa vaccine and gave non-engineered VSV to two others, then all six monkeys were infected with Lassa.

Of the six, none of the four immunized vaccinated monkeys became ill but the other two died.

Dr. Heinz Feldmann of the Public Health Agency of Canada, says that Lassa fever poses a huge public health threat in Western Africa, and while the mortality rate of the 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.

He says because of this the vaccine may have a much broader application.

Although Lassa fever is mild in most cases, it can cause epidemics of severe disease. The World Health Organization estimates that as many as 300,000 people are infected in West Africa each year and 5,000 people die of it.

There are rival vaccines against Lassa being developed.

Dutch-based Crucell has a U.S. government contract to develop a Lassa vaccine. Peregrine Pharmaceuticals is working on an antibody-based drug called Tarvacin to attack "enveloped" viruses such as Lassa, the AIDS virus, hepatitis B and C, West Nile and SARS.

The research is published in the journal PLoS Medicine.