June 28, 2005

U.S. vaccine works against Lassa fever in monkeys

WASHINGTON (Reuters) - A genetically engineered virus may
offer the first effective vaccine against Lassa fever, a
sometimes deadly hemorrhagic fever common in West Africa, U.S.
and Canadian scientists said on Monday.

The vaccine successfully protected four monkeys against
Lassa, a virus that sometimes causes high fever, internal
bleeding and which kills at least 5,000 people a year.

"This is the first vaccine platform shown to completely
protect nonhuman primates from Lassa virus," said Dr. Thomas
Geisbert of the U.S. Army Medical Research Institute of
Infectious Diseases in Frederick, Maryland.

Lassa is a hemorrhagic virus like Ebola, Marburg and yellow
fever but is far less likely to be fatal. It is, however, far
more common than Ebola or Marburg.

"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," Geisbert added in a statement.

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

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

None of the four immunized vaccinated monkeys became ill
but the other two died, the researchers reported in the journal
Public Library of Science Medicine.

"Lassa fever poses a huge public health threat in Western
Africa," said Dr. Heinz Feldmann of the Public Health Agency of

"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."

Lassa fever is mild in about 80 percent of cases but 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 in development.

Dutch-based Crucell has a U.S. government contract to
develop a Lassa vaccine. Peregrine Pharmaceuticals Inc. 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.