Bird flu latest disease to jump to humans
Updated: 2006-02-20 09:39
Humans risk being overrun by diseases from the animal world, according to
researchers who have documented 38 illnesses that have made that jump over the
past 25 years.
That's not good news for the spread of bird flu, which experts fear could
mutate and be transmitted easily among people.
There are 1,407 pathogens — viruses, bacteria, parasites, protozoa and fungi
— that can infect humans, said Mark Woolhouse of the University of Edinburgh in
Scotland. Of those, 58% come from animals. Scientists consider 177 of the
pathogens to be "emerging" or "re-emerging." Most will never cause pandemics.
Experts fear bird flu could prove an exception. Recent advances in the
worldwide march of the H5N1 strain have rekindled fears of a pandemic. The virus
has spread across Asia into Europe and Africa.
Controlling bird flu will require renewed focus on the animal world,
including the chickens, ducks and other poultry that have been sacrificed by the
tens of millions to stem the progress of the virus, experts said at a news
conference late Sunday at the annual meeting of the American Association for the
Advancement of Science.
"The strategy has to be looking at how to contain it in the animal world,
because once you get into the human side, you're dealing with vaccines and
anti-retrovirals, which is a whole new realm," said Nina Marano, a veterinarian
and public health expert with the National Center for Infectious Diseases.
Bird flu has killed at least 91 people — most of them in Asia — since 2003,
according to the World Health Organization. It appears to kill about half the
people it infects. However, should it mutate so it can pass from human to human,
it likely will grow far less deadly, said Dr. Stanley Lemon, of the University
of Texas Medical Branch at Galveston.
"It is very unlikely that it would maintain that kind of case mortality rate
if it made the jump," Lemon said.
Each year, one or two new pathogens and multiple variations of existing
threats infect humans for the first time. That pace appears to be unsustainable
in the long run because it would imply that people run the risk of being
overrun, Woolhouse told reporters.
"Humans have always been attacked by novel pathogens. This process has been
going on for millennia. But it does seem to be happening very fast in these
modern times," Woolhouse said.
Woolhouse argues that either many of those diseases and other afflictions
will not persist in humans or that there is something peculiar today allowing so
many of them to take root in humans.
One explanation may be the recent and wide-scale changes in how people
interact with the environment in a more densely populated world that is growing
warmer and in which travel is faster and move extensive, Marano said. Those
changes can ensure that pathogens no longer stay restricted to animals, she
added. Examples from recent human history include HIV, Marburg, SARS and other
That prospect leaves open the question of what future threats await humans.
"It always surprises us. We think that avian flu will be the next emerging
disease. My guess is something else might come out before that," said Alan
Barrett, of the University of Texas Medical Branch at Galveston. "It's very hard
to anticipate what comes next."