WHILE WE ARE under siege by microbes spread by
terrorists, we face what is probably a worse threat from pathogens that we
encounter naturally as part of our human ecology. This important fact is
getting overlooked in the national panic over anthrax.
One reason for the complacency is that as baby boomers, many of us grew up
unconcerned with infectious diseases. We benefited from a series of public
health measures, including a secure water supply and vaccines and antibiotics
that rendered harmless the microbial scourges of the past - polio, smallpox,
diphtheria and the like.
But now microbial pathogens are regaining their dominion over us.
Tuberculosis and other bacterial diseases, once controlled, have re-emerged as
public health threats, and deadly new viruses enter the human population each
How are bacterial and viral pathogens in nature defeating our best efforts?
They are very, very good at evolution, and they are evolving extremely
effective means to thwart the antibiotics and vaccines that once controlled
Why are they so good at evolution? For one thing, they multiply faster than
we do. A bacterial populations can double in a few hours, but we humans take
decades to do that. Every time they reproduce, they have a chance to try out
any mutations that may have occurred to make them more resistant.
But just as important, bacteria have the ability to capture genes from
other species of bacteria and claim them as their own. So when an effective
antibiotic resistance evolves in any bacterial species, however harmless, it
can eventually be passed to other species that threaten humans. The bacteria
causing tuberculosis have now accumulated resistance to nearly every available
antibiotic by transfer from other bacterial species. We unwittingly promote
this evolutionary process when we take antibiotics indiscriminately.
This gene-trading happens naturally without any help from biotechnology.
But bioterrorists could put it to use. What's next in bioterrorism might be the
dissemination of anthrax bacteria that have been given antibiotic resistance
genes through biotechnology. The weaponized anthrax produced by the Soviet
Union was made resistant, but fortunately, the recent anthrax attacks in this
country did not use this engineered strain.
Bacteria in nature pick up all kinds of genetic adaptations from other
species, not just antibiotic resistance. The genome projects reveal that
typically 5 to 30 percent of a bacterium's genes have been transferred from
other species. In pathogens, many of these genes confer virulence (the ability
to make people sick). Again, bacteria have done this, without biotechnology,
for millions of years.
Bioterrorists could add to the virulence arsenal of a pathogen by giving it
genes from other pathogens. Or they could turn a harmless but common microbe
into a dangerous one by giving it virulence genes from a pathogen.
Viruses in nature have the ability to evolve around our immune system. The
influenza virus has several times this century shifted its immunogenic
properties, so our natural immunity or vaccination against last year's virus
may not help us against this year's model. How? They take up, from other
viruses, genes for alternative forms of the surface proteins that enable our
immune system to recognize them.
Wearing a new coat, they slip by unnoticed, multiply in our bodies and make
us sick. A natural shift in the influenza virus in 1918 led to a pandemic that
killed 20 million people (more than died fighting World War I).
I worry that the smallpox virus could be altered to incorporate surface
proteins from another virus, making the current vaccine ineffective. I am not
giving away any trade secrets here. These ideas, and more, are all in the
We are under siege by bioterrorists, but long after each of these murderers
is apprehended, we will still be under siege by pathogen evolution. Microbes
will continue to evolve resistance to antibiotics and other means of thwarting
our public health defenses. The next influenza could be as virulent as the 1918
Our crisis in bioterror has brought to our attention the urgent need for
research on infectious diseases. I hope that when this crisis has passed, we
can redirect our urgency from the pathogens of terrorists toward the
potentially more dangerous onslaught from Mother Nature.