Media advisory issued August 23, 2002, effective immediately.
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Verifying Virus Facts: What is West Nile Virus?

ARDMORE, Okla. — With reports of West Nile virus spreading westward across the United States into Oklahoma and Texas and the human death toll creeping upwards, a wary public is beginning to ask some basic questions:

How dangerous is this virus? Why do viruses make us sick?

And even: What is a virus?

Marilyn Roossinck, Ph.D., with the Plant Biology Division of the Noble Foundation headquartered in Ardmore, Okla., has been studying viruses for years. Although she primarily deals with plant viruses, Roossinck says viruses in plants and those in animals share many traits and operate basically the same.

"Viruses are among the simplest and smallest living entities. They often contain only their genes, wrapped up in a neat little package of protein," Roossinck said.

"Nearly everything they need to complete their life cycle must be borrowed from their host. Their genes, in the form of RNA or DNA, are a blueprint that directs the host to make more copies of themselves. This is one reason why it is so hard to treat viruses with drugs, because whatever kills the virus usually kills the host cells, too. Traditional antibiotics combat bacterial infections, but do not affect viruses."

Although concern about the West Nile virus has risen in recent years with its spread from the East Coast west, usually carried by birds, Roossinck, who got her Ph.D. from the University of Colorado School of Medicine, points out that the illness is not a new one.

"West Nile virus has probably been infecting humans for much longer than HIV," she said. "It is common in other parts of the world, including Africa, Eastern Europe and the Middle East, but it was only identified in the United States in the late 1990s. The first human infection was confirmed in New York in 1999."

Roossinck, also an adjunct professor at both Oklahoma State University/Stillwater and Texas A&M University/College Station, points out other viruses that are very similar to West Nile, such as St. Louis encephalitis virus, have been in the United States for a long time.

However, she also stresses that unlike St. Louis encephalitis, West Nile virus rarely causes disease in people.

"Only a few percent of the individuals infected with West Nile virus actually get sick," she said. "Most people are not even aware they have the virus. Of those who do have symptoms, the severe form of the disease is even more rare."

"The virus RNA is covered by a protein coat that the virus instructs the host to make," Roossinck explains. "On the outside, the virus has a membrane that it steals from the host before it leaves the host cell. Having this membrane on the outside means the virus is very vulnerable, because the membrane cannot survive any exposure to air or water.

"That is why you can only get it by being directly injected by a mosquito. You cannot get it by touching someone with the virus, or by ingesting the virus. It has to get directly into your bloodstream to infect you," Roossinck said.

"If you, or an animal are infected by the virus, a mosquito that bites you can become infected by the virus. The virus multiplies in the mosquito, and then the mosquito can pass it on to its offspring through the eggs, which grow into adult mosquitoes that can pass on the virus to other humans or animals."

Because mosquitoes play such a dominant role in the transmission of the illness, health officials stress the need for the public to eliminate standing, stagnant pools of water conducive to mosquito reproduction; spraying exposed skin with a strong insecticide before going outside, especially early in the morning and later in the day; wearing long-sleeved shirts and pants to protect skin from mosquito bites; and spraying mosquito larvae-infested water with appropriate insecticides.

So far, no human cases of West Nile virus have been reported in Oklahoma, although they have been confirmed in the neighboring states of Texas and Louisiana, the latter with the most deaths attributed to the disease in the U.S.

"The only good protection against the virus is mosquito control," Roossinck stressed. "Once a person is infected with the virus, it is believed that they have immunity to further infections of the illness. Scientists are working on a vaccine for the virus, but so far, there isn't one available."

Why do viruses make us sick?
Most viruses do not cause any harm, and some are actually a benefit to their hosts. Some plant viruses, like the ones that cause striping in tulips, were once considered extremely valuable. According to medieval records from Holland, tulip bulbs infected with this virus sold for as much as a fully laden ship.

In addition, since viruses also infect bacteria, they have been used to control bacterial infections. This is a current strategy being used to help control Salmonella in chickens.

The viruses that have gotten the most attention, however, are those that cause disease, and this bias has given viruses a bad name. Usually, a virus is only a problem when it is in the wrong place at the wrong time. HIV, the virus that causes AIDS, recently got into the human population from chimpanzees. The chimp version does not cause any disease, but the virus is not adapted to humans, so it disrupts many aspects of the immune system in the process of completing its life cycle in humans.

The West Nile virus can cause disease and even death in humans, even though it has been infecting humans for a long time. But this is rare, and occurs most frequently in people who have poor resistance to disease for other reasons.

Facts about the West Nile virus:

• West Nile virus is a small virus. It measures about 50 nanometers across. A human cell averages about 10,000 nanometers across. A nanometer is one one-millionth of a millimeter, and there are 25 millimeters in an inch.
• The virus has an RNA genome of 11,000 subunits called nucleotides. In comparison, each human cell contains a copy of the human genome with about 3 billion nucleotides, almost 300,000 times as many as West Nile virus.
• For more information about West Nile virus, including updates on human cases, go to the Web site of the Centers for Disease Control at http://www.cdc.gov/ncidod/dvbid/westnile/index.htm.
• For more information on mosquitoes and how you can help control them, go to http://www.epa.gov/pesticides/citizens/mosquito.htm#fight.

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Photos:
Dr. Marilyn Roossinck

(190k JPEG)

The Samuel Roberts Noble Foundation, headquartered in Ardmore, Okla., is a non-profit organization conducting agricultural, forage biotechnological, and plant biology research; providing grants to numerous non-profit charitable, educational and health organizations; and assisting farmers and ranchers through educational and consultative agricultural programs.

To learn more, visit the Noble Foundation Web site at http://www.noble.org.

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