New Facts on West Nile Virus

By Ellen Kuwana
Neuroscience for Kids Staff Writer
October 18, 2002
Updated on January 27, 2003

New Routes of Transmission Found

West Nile Virus (WNV) is usually transmitted by mosquitoes, but scientists now know that the virus can be transmitted through blood transfusions and organ transplants. However, the chance of contracting the virus this way is extremely low, and there is NO risk of getting WNV by donating blood.

The evidence for the transmission of WNV through blood transfusions comes from a 24-year-old woman who was in an automobile crash. She received blood from 18 donors. Despite efforts to save the woman's life, her injuries were too great, she died, and her organs were "harvested" for transplantation. Four people received organs from this car crash victim and they all developed WNV encephalitis. One transplant patient died as a result of WNV complications.

What was the source of the WNV? The woman who was in the car crash did not appear to have the virus when she was admitted to the hospital because a sample of her blood before the transfusion showed no sign of WNV. Four days after the blood transfusions, however, one of the original blood donors developed chills, fever and a headache. Scientists obtained a sample of this donor's blood from the supply that had been banked and they found WNV. Thus, they concluded that the car accident victim did indeed contract WNV from the blood transfusion (although they can't be 100% sure that she didn't get WNV from a mosquito bite). WNV from the car crash victim's organs then infected the recipients.

At this time, it is not known how long WNV stays in the bloodstream of an infected person. It is promising, however, that once symptoms appear, the virus is difficult to detect. This suggests that the virus is cleared within a few days after a mosquito bite. As long as blood donors are vigilant about calling the blood bank if they develop any WNV-like symptoms, the blood supply should remain relatively safe. One suggestion is that people who will be undergoing elective surgery should bank their own blood in advance.

WNV Can Cause a Polio-like Paralysis

Poliomyelitis paralysis is a disease that causes spinal cord damage and was common in the US before a vaccine was developed in 1955. The October 17, 2002, issue of The New England Journal of Medicine described seven cases of WNV patients who had one-sided paralysis. This paralysis is painless and doesn't involve loss of sensation. In other words, unlike a complete paralysis, these patients could feel touch and temperature, but were unable to move one side of their body. It is important that doctors are aware that WNV can cause such symptoms, so that the patient is not misdiagnosed with food poisoning, a stroke, or a neurological disorder such as Guillain-Barre syndrome (which usually involves both sides of the body). Research by Neurologist Arturo Leis at the Methodist Rehabilitation Center in Mississippi suggests that WNV targets spinal cord neurons that control motor cells, but spares sensory neurons. The patients with WNV paralysis have had little improvement over the past one and a half months and it is unknown how long the paralysis will last.

It is a good thing that the warm weather of summer is over. With autumn here, and cold weather approaching, mosquitoes' time in the sun is over. Next summer, however, is another story.

Did you know?

  • Approximately 4.5 million persons receive blood or blood products annually. (Source: CDC - blood transfusions and organ donations.)

  • In September 2002, the CDC pledged more than $6.3 million to states to combat WNV. This is in addition to $11.3 million that was awarded to states in August. Total CDC funding for WNV research and protection is approximately $35 million so far. (Source: Department of Health and Human Services.)
  • In 1999, there were 62 cases and 7 deaths from West Nile virus in New York City. In the following three years, the virus spread to all states except Oregon, Nevada, Utah and Arizona. In 2002, there were approximately 2500 cases and 246 deaths from West Nile virus.
The Centers for Disease Control (CDC) has public hotlines for questions: 1-888-246-2675. Spanish speakers can call 1-888-246-2857 and the number for hearing-impaired is 1-866-874-2646.


  1. CDC - West Nile Virus questions and answers
  2. "West Nile Virus Can Paralyze, by Deborah Hill, inScight, September 23, 2002.
  3. "US Officials Warn of a West Nile Risk from Transfusions," By Lawrence K Altman, New York Times, September 20, 2002.
  4. "Another Polio?" Science News, September 28, 2002, Vol. 162, pages 197-198.

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