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Four Corners
On May 14, 1993, in a rural community in the Navajo Nation near Gallup, New Mexico, an unknown microbial killer swiftly claimed the life of a young athlete. Within a week, his fiance and four others died from the disease.

Dr. Stuart Levy and Dr. Fred Koster quickly realized they had a mystery on their hands and a potentially deadly epidemic. However, before they could fight the outbreak, they had to find its cause. This was a disease they had never seen before. They ruled out many of the known viruses and bacteria, and lab tests conducted at the University of New Mexico searching for the cause of the disease were unsuccessful.

Once or twice a week, a new patient was admitted to the hospital, and half of them quickly died. For no apparent reason patients would quickly develop flu-like symptoms and then suffer a heart attack. "We couldn't at that stage predict who was going to live and who was going to die," explains Dr. Levy.

(deer mouse)Finally, researchers at the Centers for Disease Control and Prevention (CDC) in Atlanta identified the culprit from victim's blood and tissue samples: it was a Hanta virus. These particular viruses are not transfered directly between humans, they are only transfered from animals to humans. In this case, a increased population of deer mice was responsible for the outbreak.

Viruses are the smallest of microbes and the simplest of all living things. They are so simple, some biologists don't consider them to be living things. Their only function is to inject their genetic code into other cells. Viruses hijack the host cells' reproductive systems, forcing them to automatically produce new viruses. Disease is frequently the result of this parasitic behavior. When a virus hijacks a cell, the cell can be rendered useless or destroyed.

To defend against viral attacks, all living creatures have immune systems. One of the primary components of the human immune system is the white blood cell. These cells patrol the body and destroy any foreign cells or particles they find. Ironically, this normal defense was responsible for the deaths of the Hanta virus victims.

Inside the lungs, small air sacks are surrounded by blood vessels. White blood cells patrol these blood vessels on the lookout for invaders. When the Hanta virus enters the air sacks, the white blood cells react. They emit strong chemicals meant to destroy the virus, but they also weaken the blood vessels. Soon, blood plasma leaks into the air sacks, eventually filling them with fluid. Therefore, the strongest people are the most at risk because their bodies react so strongly.

Hanta virus is not an effective virus. Because it quickly kills its host, it soon runs out of hosts to invade. Other invaders, such as the Salmonella bacteria, have evolved to be less deadly so they survive longer with their hosts.

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