WORM'S EYE

Viruses exist to nab your cells and use them for their own reproductive purposes. They have to, because a virus is nothing more than a few strands of rogue DNA (or rogue RNA, DNA's single-stranded cousin) wrapped in a protein coat to keep the draft out.

They are not cells, and they have none of the internal structures that cells use to go about the business of life, which is, generally, to make more life. No, viruses are just genetic material looking for a free ride--looking to hijack a host cell and make its machinery do the invader's reproductive bidding.

Rule for Viral Success #1:
Mutation, Mutation, Mutation

With so little to call their own, how have these biological pirates survived for so long? The answer lies in two traits that give viruses superb evolutionary advantages: superfast reproduction and genetic mutations.

Viruses live to reproduce. Although they must do this within host cells, once inside, viruses replicate with enough abandon to shame a rabbit. Like some evil biological Xerox machine, they reprogram the machinery that host cells normally use to copy their own DNA and use it to spit out copy after copy of themselves.

Genetic mutations add insult to injury. With so much reproduction going on, viruses can mutate almost as fast as they propagate. And each mutation stands a good chance of conferring advantageous survival and adaptation characteristics on the next generation of viral invaders.

Rule for Viral Success #2:
Pick a Likely Victim

Viruses invade all kinds of cells, including plant cells, animal cells, fungi, even bacteria. Each virus tends to have a very specific M.O., though. Which host cells look like the best victims to any given virus depends on the unique proteins found on a virus's protein coat, as well as on the protein receptors found on the poor target cell.

Some viruses recognize the general receptors that occur on many different kinds of cells. The virus for rabies, for example, can invade so many different kinds of cells that it can span species, infecting rodents, dogs, and humans.

Other viruses are more restricted and can invade only specific kinds of cells. The common cold virus, for example, can invade only the cells lining the human upper respiratory tract. It's a picky thief.

Rule for Viral Success #3:
Make It an Inside Job

Viral entry mechanisms are as diverse as viruses themselves, which is why viruses often elude drug treatments. Some enter a target cell by binding to a specific receptor and passing through the host cell membrane to the cell interior. Others don't even need to enter the cell, but simply attach to the surface and use a needle-like structure to inject their DNA right in.

Once viral genes are inside, the virus begins its cycle of replication. It exploits the host cell's supplies and machinery, forcing it to copy viral genes and to synthesize more viral protein coats. Then, these two components come together to form copies of the virus that emerge from the host cell.

Sometimes they "bud" off the cell, like bubbling on top a simmering stew. At other, more violent times, copies simply fill the cell until it can hold no more; it explodes, releasing its viral hoard into the surrounding area.

Either way, the viral progeny go on to infect new cells--and the cycle starts again. Disease symptoms can and do result from this cellular damage. Most often, though, the sickness you feel is the result of your immune system's response to the foreign invader. And make no mistake, it will respond.

Rule for Viral Success #4:
Avoid the Cops

Your immune system's first-responders act like beat cops on patrol 24/7. Should they see anything amiss while walking the body's beat, they will make arrests. One kind of cellular cop, the phagocytes, will engulf strange viruses and digest them. Another kind, natural killer cells, recognizes suspect changes on the surface of infected cells and will release chemicals to disintegrate both virus and cell alike.

After spotting the infection, your body can launch a more specific and intensive attack. Proteins called antibodies surround, bind to, and neutralize viruses and other invaders in your bloodstream. Killer T-cells mercilessly destroy infected cells and halt systemic infection. Both help your body remember the infection and mount a faster response to the same invader next time.

Still other players merit mention. When a cell does get infected with a virus, sometimes it manages to secrete small proteins called interferons that serve to warn neighboring cells of an imminent viral invasion. These "Paul Revere" proteins work by encouraging neighboring cells to synthesize proteins that can interfere with viral replication.

Christina Catron and Michael Himick
October 27, 2004

Want to learn more?
Read what the CDC says about the flu virus
http://www.cdc.gov/flu/about/disease.htm

Get answers from the CDC about the flu vaccine
http://www.cdc.gov/flu/about/qa/0405season.htm

KnowledgeNews.net * 123 South 6th Street * Marshall, Illinois 62441 * USA

The World Health Organization is worried--worried that the world is due for another killer flu, as bad as the one that killed millions at the end of World War I. The influenza chief of the United Nations, Klaus Stohr, even goes so far as to say, "We believe that we are closer to the next pandemic than we ever were."

The question is, what can the world do about it? Yesterday and today, health experts from governments and vaccine companies worldwide have gathered in Geneva to come up with answers. At KnowledgeNews, we're looking back at the 1918-19 flu, which is exactly what the experts fear most.

Today's Knowledge
The Deadliest Flu Ever

In 1918 and 1919, nearly one-fifth of the world's population caught the flu. And not just any flu--the deadliest flu ever, one of the worst pandemics in human history.

Before it was over, 2 to 3 percent of those infected had died. That's at least 20 million people worldwide, more than twice the number killed in all of brutal World War I.

Swift and Fatal

Military bases served as incubators for the virus, in America and Europe especially. In fact, a huge number of casualties in World War I came from the flu, rather than from enemy fire. Within months, following troop movements and trade routes, the virus had traveled around the world.

The illness was so fast and so deadly that doctors couldn't even believe it was influenza. It wasn't like any flu they had seen before. A patient who started to feel under the weather on Monday was often dead by Wednesday. Many patients turned a blue-gray hue, as fluid built up in their lungs. "It is only a matter of a few hours then until death comes, and it is simply a struggle for air until they suffocate," reported a doctor at a military base near Boston. "It is horrible."

Even worse, this virus devastated people for whom flu is normally just an inconvenience. Healthy men and women in their twenties, thirties, and forties were dropping dead on the street on their way to work or the market. How could this be the flu? Some even speculated it was a plot by the Germans, or a side effect of the mustard gas used during World War I.

Dramatic Mutation

But it was the flu--a horrible new strain, but just the flu. Every few decades, the flu virus, which mutates at least a little bit every year, undergoes a dramatic change. This new virus is especially dangerous because no one has built up an immunity to it. The virus of 1918-19, from the time it likely got started in Asia, was this kind, different enough from previous strains that few people were immune.

Because flu spreads through the air, it was also frighteningly easy to get infected. All you had to do was breathe the air that a sick person had just coughed or sneezed into. The most dangerous place you could be was in a crowd.

Unfortunately, it was hard to avoid crowds in 1918. Hundreds of thousands of soldiers were being packed into barracks and onto troop ships. And huge military parades and war-bond rallies helped the virus make the leap from soldiers to the civilian population.

Flu Crosses the Nation

By autumn of 1918, life in big cities had become nightmarish. In one month--October 1918--nearly 200,000 Americans died from flu. Medical care was hard to come by, because so many doctors and nurses had been dispatched to Europe to care for the troops (and because many of those who stayed got sick, too). Churches, theaters, and taverns closed. In some cities, even funerals were limited to 15 minutes.

When one person in a family got sick, the flu usually spread to everyone else in the house. Volunteer nurses, arriving with broth and clean sheets, were seen as saviors by people too ill or too poor to get to a doctor. "In some cases," a New York City nurse wrote, "the nurses were even locked in the house by the patient's friends, or kidnapped on their rounds, so panic-stricken had people become."

The East Coast was ravaged in September 1918, and it took only a few weeks for the epidemic to spread to the West. In San Francisco and Seattle, wearing gauze masks was required by law. In Prescott, Arizona, the town council made it illegal to shake hands. Other towns quarantined themselves, forbidding trains from stopping, only to fall ill when they welcomed the postman. On the playground, children had a new jump-rope rhyme:

I had a little bird, and its name was Enza
I opened the window, and in-flew-Enza.
It’s a Small World

By the time it had run its course, the 1918-19 flu killed more than half a million Americans. Beyond the United States, the death toll was even more appalling. What Americans called the "Spanish flu" (incorrectly believing that was where it started) cropped up all over the world.

Germany, France, and the United Kingdom each lost at least 200,000 civilians between June 1918 and May 1919. More than a half a million Italians died. In poorer and more densely populated areas, the death toll was catastrophic. In parts of Mexico, more than 10 percent of the population perished. On South Pacific islands, more than 20 percent did. In India, at least 12 million people died from flu.

The death toll for the whole world is difficult to know, but the most conservative estimate is that 20 million people died. Many researchers double that number, and some go so far as to say that the death toll could have reached 50 million.

The 1918-19 pandemic was extreme, but not unprecedented. The World Health Organization has records showing that there have been 31 documented influenza pandemics since 1580, most recently in 1969. The bad news is that medical researchers say we are overdue for another devastating flu.

Colleen Kelly
November 12, 2004

Want to learn more? See how the flu spread across the United States http://www.pbs.org/wgbh/amex/influenza/maps/index.html

KnowledgeNews.net * 123 South 6th Street * Marshall, Illinois 62441 * USA
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