research needed on monkey virus found in humans
HOUSTON--(Jan. 19, 1999)--A
monkey virus that scientists have long thought does not infect humans has been detected in
human tumors, but whether the virus caused the tumors has not been proven.
"Evidence is mounting that simian virus 40 (SV40) infects humans and is associated
with certain types of human tumors," said Dr. Janet Butel, head of the division of
molecular virology at Baylor College of Medicine in Houston.
"This association with human disease might lead to new approaches for diagnosing
and treating certain types of cancers and other illnesses, but further studies are needed
to determine whether SV40 plays a causative role in the tumors," she said.
Butel and Dr. John Lednicky, also a Baylor molecular virologist, presented an overview
of what is known about SV40 in the Jan. 20 issue of the Journal of the National Cancer
SV40, which originated in the rhesus monkey, was discovered in 1960 as a
contaminant of polio vaccines given to millions of people from 1955 through early 1963.
Monkey kidney cells that were used to grow the polio vaccine were unknowingly contaminated
Although no acute illnesses resulting from SV40 were reported in people who were
exposed to the contaminated vaccines, some scientists are now concerned that the
virus might pose a cancer risk to humans. Antibodies to SV40 have been detected in up to
10 percent of adults born after 1962, so possible exposure to the contaminated polio
vaccines would not explain how these people were infected with the monkey virus, Butel
"There must be an alternate source of human infection by SV40," she
Advanced genetic technology has made it possible to detect DNA from SV40 in several
types of human tumors, including brain tumors in children, bone tumors, and tumors
associated with exposure to asbestos. Investigators in the United States and Europe have
confirmed that this DNA is from authentic SV40 and was not caused by contamination of
specimen samples in the laboratory,
Butel said. Genetic analysis has also shown that contrary to previous belief, there are
multiple strains, or variations, of SV40.
"This raises the possibility that some strains of the virus are more likely to
cause disease or induce certain types of tumors in humans, but that needs to be
investigated in further studies," Butel said.
SV40 induces tumors in mice and hamsters and transforms many types of cells, including
human cells, in laboratory studies. Healthy rhesus monkeys infected with the virus don't
develop obvious signs of disease. But in monkeys infected with the AIDS virus, SV40 has
been detected in their brains and other organs.
"This suggests that humans with compromised immune systems might be at greater
risk of SV40 infection," Butel said.
Because the original source of SV40 strains now present in humans is unknown, Butel
advocates the need for more research on how the virus can be transmitted.
"It is of no small irony that SV40, once having been found as an unrecognized
contaminant of a widely heralded viral vaccine, might itself one day become a candidate
for vaccine development," she said.
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