CONTACT: Jim Sliwa
November 10-15, 2001: (404) 221-6821
EMBARGOED UNTIL: November 12, 2001,
2:30 p.m. EST
HEPATITIS E RECOVERED FROM RATS IN LOS ANGELES
ATLANTA -- Researchers from the
National Institutes of Health have recovered a virus
similar to the hepatitis E virus (HEV) from rats in Los
Angeles, California, a finding that may explain high
levels of HEV exposure in inner-city residents without
disease. They report their findings today at the 50th
Annual Meeting of the American Society of Tropical
Medicine and Hygiene.
"There is a fair amount of
antibodies to HEV in humans in the United States,
suggesting exposure, but very little clinical
manifestations of the disease," says Robert
Purcell, Co-Chief of the Laboratory of Infectious
Diseases and Head of the Hepatitis Viruses Section of
the National Institute of Allergy and Infectious Disease
and primary author of the study.
HEV infection is one of the most
common causes of hepatitis in central Asia. Unlike some
other forms of hepatitis, like hepatitis B and C, HEV
infection is self-limiting, lasting 1 to 4 weeks, and is
generally not life threatening, except in pregnant women
where fatality rates of 15 to 20 percent have been
reported. According to the Centers for Disease Control
and Prevention, most cases of HEV disease in the United
States have occurred among travelers returning from
developing countries. Still, between 1 and 5 percent of
healthy blood donors in the United States have HEV
antibodies in their blood with rates over 20 percent in
some inner city areas.
Swine have been shown to be a
possible source of HEV exposure and the swine virus,
while quite similar to the human virus, does not appear
to cause disease, at least in swine.
"However, most inner-city
residents do not come into contact with pigs on a
regular basis," says Purcell. "That was when
we got interested in looking at rats."
Previous studies have shown that a
high percentage of wild rats in the United States have
antibodies against HEV, suggesting previous infection.
While pigs are not ubiquitous in urban areas, rats are.
Because HEV infections are relatively short-lived,
though, recovering the virus from rats can be very
"What we did in this study was
try to recover the agent from wild rats. You have to be
lucky to find a rat that is acutely infected," says
To increase their odds, Purcell and
his colleagues examined only rats that did not have
antibodies to HEV, hoping that there would be a chance
that those rats were incubating the virus. They also
included rats that tested negative for long-term
antibodies against the virus (that would appear after
infection) but tested positive for shorter-term
antibodies (the type that would appear during acute
infection). They tested 80 rats from Los Angeles County
and Orange County in California, Baltimore and Hawaii,
extracting sera and injecting it into laboratory rats.
Three of the laboratory rats that had been inoculated
with sera from rats in Los Angeles developed disease.
Purcell warns that they have only
recovered the virus and have yet to isolate and
characterize it. "HEV doesn't grow in laboratory
cell cultures. So far we've only recovered the rat agent
from wild rats and have transmitted it to laboratory
rats, so we know there's a transmissible agent there and
it is serologically related to HEV," he says. He
does believe the virus may end up being significantly
different from human and swine HEV as the primers used
to amplify RNA of those viruses do not work on this new
It is possible that these infected
rats may contribute to the the high rates of humans with
HEV antibodies in inner cities, says Purcell, but more
tests need to be done. For the next step they must
develop a specific antibody diagnostic for the rat virus
and test humans with it to see if they have been
infected by the rat virus.
Exposure does have its upside.
Having antibodies to HEV, regardless of the source,
appears to protect against future disease. In a related
study, Purcell will also present information on the
results of an experimental vaccine against HEV. It has
been tested in primates with promising results and is
currently in human trials. The results in humans could
be available as early as next year.