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The Worst Bioterrorist May Be Nature Itself

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

decade.

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

them.

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

newspapers.

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

flu.

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.

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