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Killer in the Bloodstream
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Even people familiar with meningococcal disease are astonished at the rapidity
with which this rare though deadly illness can ravage the body. Within hours,
patients can go from perfectly healthy to mortally ill. What makes these
microbes so lethal? In this animated feature, follow the progression of
meningococcal bacteria as they race through the bloodstream, wreaking havoc on
a scale few diseases can match with such lightning speed.—Peter Tyson
Assaulting the body
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Meningococcal bacteria can cause two life-threatening conditions: meningitis
and sepsis.
In meningitis, the bacteria attack the lining around the brain called the
meninges. They breach the meninges to infect the fluid running into the spinal
cord. One clear, early symptom is a stiff, sore neck. The meninges and brain
start to swell, putting pressure on essential nerves. Fewer than one in 50
victims of meningococcal meningitis will die, but survivors are often left deaf
or with permanent brain damage.
The other type of infection is much more deadly, killing roughly 20 percent of
its victims. It's a severe blood poisoning called meningococcal sepsis that
affects the entire body. The bacterial toxins rupture blood vessels and can
rapidly shut down vital organs.
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Entering the throat
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Meningococcal bacteria commonly live in the human throat without causing
harm. But sometimes they break through the throat's lining and enter the
bloodstream. The reasons why and how are only now being unraveled. Damage to
the throat from flu and other infections could be one factor.
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Hurtling through the bloodstream
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Every meningococcal bacterium is surrounded by a slimy outer coat that contains
a poisonous chemical called an endotoxin. While many bacteria produce
endotoxin, the levels produced by meningococcal bacteria are 100 to 1,000 times
greater than normal.
As the bacteria multiply and move through the bloodstream, they shed bubbles
that contain concentrated amounts of toxin. These bubbles also act as decoys,
confusing the body's immune system. The endotoxin targets the heart, affecting
its ability to pump and also causes blood vessels throughout the body to leak.
As every vessel starts to hemorrhage, major organs like the lungs and kidneys
are damaged and eventually destroyed.
Two things can stop this runaway infection before the patient dies: antibiotics
like penicillin, and the patient's own immune system.
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Attacked by antibiotics
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As soon as doctors suspect meningococcal disease, patients are given a large
dose of antibiotic, usually penicillin. Penicillin flowing through the
bloodstream rapidly kills the bacteria. But it cannot penetrate the bubbles
that contain the endotoxin. In fact, as the bacteria are killed, they release
even more toxin. It takes up to two days for the poison to be cleared from the
body and the siege to end.
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Killing tissue
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As soon as the bacteria entered the bloodstream, unleashing the poisonous
endotoxin, the body began responding on its own. White blood cells, the
hunter-killers of the immune system, locked onto the bacteria, engulfing them
and coming into contact with the endotoxin.
The poison causes the white cells to release chemicals that make the blood
vessel walls sticky. The white cells then become trapped on the walls, leaving
a trail of damage. Gradually the lining of the blood vessels is stripped away.
And as the damage increases, the vessel walls break up and pieces fall off. The
blood's repair cells, called platelets, rush to plug up the damaged areas.
Dangerous clots begin to form. The proteins that normally prevent clotting have
all been destroyed. Within minutes the small blood vessels of the body are
completely blocked. The damaged blood vessels disintegrate, and blood and other
fluids hemorrhage into the surrounding tissue. It is this cascade of events
that causes the distinctive rash that appears beneath the skin and kills tissue
throughout the body.
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