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TREATMENTS

How the body fights back

By Raja Mishra, Globe Staff, 11/4/2001

   
 KEEPING SAFE

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Not all terror threats equal

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How to talk to your kids
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How anthrax is diagnosed
Inside a bacterial invasion
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More anthrax coverage

Anthrax kills in self-defense. if12

If you were to ingest anthrax spores into your lungs, your immune system would swarm the bacterial invader. But the microbe's defense is strong and lethal. Without reinforcements, in the form of antibiotics, your side would probably be overwhelmed. You would die.

How does anthrax kill? Why couldn't the body fight it off? How can I improve my chances if infected?

Such questions, once pondered only by scientists and soldiers, are now commonplace, as new anthrax cases turn up almost daily. The numbers are small, but the fears large.

In many ways, anthrax is a simple foe: tiny and rare, a single-cell bacterium scientists call Bacillus anthracis. Outside of animals and humans, it lives in spore form, with a tough exterior coating enabling it to survive for years or even decades in nature. But once the spores enter a living creature, the bacteria within emerge with frightening speed.

Scientists estimate ingestion of 2,000 to 10,000 spores - barely a sprinkling - is enough to kill. But new evidence from the current outbreak suggests even fewer can be fatal.

The spores can take different routes into the body. The most deadly route causes inhalation anthrax, which killed four Americans in recent weeks. In these kinds of cases, spores travel through the mouth and nose, down the trachea, into the lungs, and finally lodge in the alveoli, tiny sacks throughout the lungs that are key to breathing.

The body would sense invasion. Out come the macrophages, lethal members of the immune forces that would gobble the spores. Many spores would die on the spot. The macrophages would carry the others back to the lymph nodes, one of the bases for the army of the body's immune system.

Bacillus anthracis thrives on body tissue. The rich protein and glucose on the surface of the skin and internal organs would coax it out of its shell. It might wait for some time inside the spore, sitting inert in the body for up to two months. But as soon as it emerges, the bacteria begin reproducing, swiftly growing in number. And they deploy their own defenses.

The anthrax begins to secrete a toxin that Dr. John Collier, a vaccine researcher at Harvard Medical School, describes as a ''highly evolved missile.''

It is this toxin that kills. It consists of three proteins, one that allows the toxin to penetrate into immune cells like a syringe, one that paralyzes those cells, and one that kills them. As the body's immune cells start dying, they set off a chain reaction that decimates the body's defense system, causes hemorrhaging that floods the lungs, poisons the bloodstream, and, within days, kills.

Ninety percent of those who inhale anthrax will die if they do not receive antibiotics quickly. But only 20 percent of those with untreated cutaneous anthrax die. In these cases, the spores enter through cuts in the skin. And in cases where anthrax is ingested, when spores enter through contaminated food, the survival rate is 20 to 60 percent.

Why the better odds for people who are infected with anthrax through the skin or from food? It's not exactly clear. Scientists speculate that, in the case of cutaneous anthrax, the battlefield is local, preventing the toxins from damaging a vital organ like the lungs. The skin develops a blackish, crusty lesion. But the patient will probably survive. Scientists have few clues about why the mortality rate is lower for people who ingest anthrax, because there have been so few cases.

Even in cases where anthrax is inhaled, the body's odds improve dramatically with help from some key allies: antibiotics and vaccine.

Cipro has become a household name, but at least four other antibiotics combat anthrax. These compounds are like smart bombs: They seek and destroy the anthrax without harming much else. But they don't cleanse the body of toxins that have already been released. That's why antibiotics can save a patient only if taken early: The bacteria are killed off, and the toxin level is low enough for the body to handle.

''In order to kill you, these bacteria have to grow to very large numbers in the bloodstream,'' said Collier, the Harvard researcher.

Anthrax infections have basically two stages. The first, lasting from hours to a few days after bacteria emerge from the spores, produces intense fatigue and flu-like symptoms. At this point, antibiotics will markedly improve the chance for survival. The second stage, when toxins pile up, involves intense difficulty breathing and shock. Once this begins, death is likely.

Cipro, the most popular anthrax antibiotic, has side effects: nausea, diarrhea, vomiting, headache, rash, and restlessness. Some postal workers recently stopped their Cipro regimen because of the side effects.

And this antibiotic may, according to animal studies, cause side effects in children, including joint or cartilage damage and difficulty walking.

That said, if there is any indication you have been exposed to anthrax, those side effects are minor compared with the danger of anthrax. Doctors strongly recommend at least a 10-day course of Cipro or an equivalent antibiotic immediately.

But there is a defense system more powerful than antibiotics: a vaccine. The anthrax vaccine works much like other vaccinations; it familiarizes the immune system with the enemy by delivering a small, non-lethal dose of anthrax. Without vaccination, the immune system lacks cells that can quickly recognize and kill anthrax. Unfortunately, the vaccine is inconvenient, requiring six injections over several months, though researchers are working on a single-shot vaccine.

Anthrax vaccinations are available only to US military personnel. The stockpile is meager, and a majority of soldiers remain unvaccinated. During preparations for the Gulf War, some soldiers refused the vaccination, fearing side effects. There are no plans to stockpile or offer the vaccines to the public.

On the other hand, the vaccine to another potential bioterrorism agent, smallpox, is considered the most successful vaccine ever developed. Smallpox killed close to half a billion people during the 20th century. Smallpox is a virus, a simple DNA strand with a protein coat that can live only by taking over healthy cells. Antibiotics do not work.

Those infected develop fevers, fatigue, and pus-filled sores. About 30 percent die, though the fatality rate can be much higher in intense outbreaks.

Smallpox has been essentially eradicated. A massive global vaccination campaign beginning in the 1950s stopped the highly infectious virus from spreading. US officials fear that terrorists or rogue nations might have supplies, but called the risk slight.

In the United States, routine smallpox vaccinations ended in 1972. Full immunity lasts for three to five years, say federal health officals, who are assuming the entire US population is vulnerable to smallpox.

The government is currently negotiating with several companies to create a vaccine stockpile large enough for the nation.

This story ran on page 12 of the Boston Sunday Globe's Common-sense Guide to Keeping Safe on 11/4/2001.
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