It
was assumed that H5N1 bird flu is a rare disease that kills roughly 59 percent
of the people it infects, but a new US study published in the journal Science
suggests it may be more common and less deadly than previously believed.
The research could help alleviate concerns of
a worldwide flu pandemic that could kill millions and millions of people,
sparked by the recent lab creation of a mutant bird flu strain that can pass
easily between animals.
The World Health Organization (WHO) reported
586 human cases of bird flu since 2003, with 346 of those individuals dying —
58.6 percent. But researchers at Mount Sinai School of Medicine believe those
estimates are misleading.
Virologists at Mount Sinai said they had found
signs of infection in 1-2 percent of blood samples they had screened from more
than 12,000 people in Asia, Europe and Africa, but most people did not seek or
need treatment. And none of the screened persons died from their infections.
Their findings, which used data from 20
previously published studies, suggest that many more people have been infected
with H5N1 than the 586 officially confirmed by the WHO; and if so, the fatality
rate could be exponentially lower than the global health agency‘s report.
“The World Health Organization criteria that
are currently being used for confirmation of H5N1 infections are good for the
identification of very severe cases, but they do not pick up the cases that are
mild or asymptomatic” because such patients are unlikely to seek medical
treatment, said postdoctoral researcher Taia Wang, who led the study.
While there is no true scientific consensus
about the actual fatalities stemming from H5N1, flu experts have speculated in
the past that the WHO’s surveillance methods are flawed and misses an unknown
number of cases.
WHO spokesman Gregory Hartl acknowledged today
that the agency’s criteria for confirming bird flu cases may underreport mild
cases. But he said it was more likely that officials were missing cases of bird
flu deaths.
Peter Palese, chairman of the department of
microbiology at the Mount Sinai School of Medicine in New York, and one of the
study leaders, said the WHO’s mortality rate may be misleading because the
agency only reports cases of people who are sick enough to go to the hospital
and are lab-tested for the virus.
To be counted by the WHO, a person must have
an acute illness and fever within a week and test positive for exposure to the
H5 protein that gives the virus part of its name. Anyone sick enough to do that
is more likely to die to begin with, noted Palese.
And in countries where avian flu is present,
access to healthcare and hospitals is spotty at best, he added. Basically,
there could be a lot more people out there who get the virus and either don’t
show symptoms or don’t feel bad enough to see a doctor.
In the study, Palese, Wang and colleagues
found that in each of the 20 previous studies on bird flu, infection ranged
from 0 to 11.7 percent, though the higher figure came from people living in
close quarters with those who were infected. The overall infection rate across
the study was 1.2 percent.
The big question is how that translates to the
rest of the population. Even a two percent infection rate is a lot of people in
a group of millions. But if the WHO is only counting those who go to the
hospital, those who have the most severe symptoms of the disease, it is likely
that the number of people with the virus is higher, and the death rate would be
much lower, the researchers speculate.
But even so, that doesn’t mean that H5N1 is
benign. But it does mean that until someone studies whole populations and
checks how many people with the virus show fewer severe symptoms, it is
difficult to say exactly how dangerous bird flu is.
“We suggest that further investigation, on a
large scale and by a standardized approach, is warranted to better estimate the
total number of H5N1 infections that have occurred in humans,” the authors
wrote.
But not everyone was enthused with the study
findings.
Michael Osterholm, director of the Center for
Infectious Disease Research and Policy, which studies threats of bioterrorism,
says there are flaws in the methods used.
For instance, one of the studies included in
the analysis looked at the 1997 bird flu outbreak in Hong Kong, which,
Osterholm said, raises the number of people who were seropositive. “The virus
was a bit different,” he noted.
In a press release from the American Society
of Microbiology, Osterholm said in Hong Kong, the virus was H1N1, which is also
influenza but genetically different from H5N1.
“Palese’s paper just confuses the issue
because of the Hong Kong experience,” Osterholm told LiveScience, adding that
only more recent studies, of a virus more similar to that plaguing humans
today, should be used. In fact, doing so would reveal that 0.5 percent of the
participants were seropositive.
Osterholm published a study today in the
journal mBio showing that the virus might be even more deadly than the current
mortality rate shows. Taking an average of the studies Palese used is therefore
misleading, according to Osterholm. “If you put your head in the freezer and
your feet in the oven, of course the average temperature will be just right,”
he said.
“You could reduce the seriousness of this
virus twenty-fold and it would still exceed that of the 1918 Spanish flu,” said
Osterholm.
The 1918 H1N1 flu outbreak had a fatality rate
of about 2 percent. But it killed as many as 50 million people worldwide because
it spread easily between people.
Flu experts have been studying H5N1 to see if
it has the potential to become more contagious in people, and researchers in
the Netherlands and the United States have created strains in the lab that can
pass easily between lab ferrets, which react to influenza much the same as
humans do.
In December, however, fears of an H5N1
pandemic led a US government insecurity advisory panel to seek restrictions on
the publication of that research. That request angered scientists who said they
needed to share their findings in order to develop vaccines and prepare for a
possible worldwide pandemic. But the panel, of which Osterholm is a member,
said the data could be dangerous if it fell into the wrong hands.
The issue is still under debate and
researchers said they will delay publication of their findings while the matter
is sorted out. An international group of experts meeting at WHO headquarters in
Geneva last week decided that the studies should eventually be published, but further
risk assessment is needed before that can happen.
Source: RedOrbit Staff & Wire Reports
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