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 percent 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 antiretrovirals, which is a whole new
realm," said Nina Marano, a veterinarian and public health
expert with the National Center for Infectious Diseases.
According to the World Health Organization, bird flu 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 for the last 25 years, one or two new pathogens and
multiple variations of existing threats have infected humans for
the first time. Without speculating about earlier infection rates,
Woolhouse told reporters it appears impossible the human species
could endured such a rapid pace of new infections over thousands
of years.
"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 viruses.
That prospect leaves open the question of what future threats
await humans.
March 6, 2006 |
