West Nile virus blood test may be months, years away

WASHINGTON -- Health officials were trying to determine Wednesday if West Nile virus can be spread through blood transfusions. But any test to screen donated blood for the sometimes deadly disease is at least months, maybe years, away, they said.

Still, they emphasized that the blood supply is very safe and the risk of contracting West Nile from blood is significantly lower than the risk of forgoing any procedure that would require a transfusion.

West Nile, which emerged in the United States just three years ago, has exploded across much of the country this summer, with 673 cases and 32 deaths. But concern increased Tuesday when officials confirmed that at least three of four people who had received organs from a Georgia woman had contracted the disease. One died.

Officials said they are convinced that these patients got the disease through their transplants, though they do not yet know whether the virus can be spread through blood as well.

Dozens of epidemiologists at the Centers for Disease Control and Prevention in Atlanta and the CDC lab in Fort Collins, Colo., were trying to figure out how the organ donor, a Georgia woman who died in a car crash, got West Nile.

She had received blood from more than 60 donors before she died, and scientists were tracing those blood donors to see if any of them have the virus. They are also tracking down about a dozen other people who had received transfusions from the same donors.

It is possible the organ donor may have contracted West Nile from a mosquito bite, as others have. It also is possible that the virus can be spread through organ transplants but not through blood. Still, health officials suspect that blood can carry the virus, at least in some cases.

For now, they are reminding blood banks to be sure that no one with a fever or who appears ill donates blood, which could eliminate those with mild West Nile symptoms. They are also urging organ procurement organizations to be aware of the issue.

Ultimately, a screening test is probably needed, said Dr. Lester Crawford, acting commissioner of the Food and Drug Administration.

Even so, testing for the virus is complicated. Some of the tests that are used to diagnose West Nile in sick people will not pick up the virus in donated blood. Other more promising tests would require significant improvements to be practical on a mass scale, enabling blood banks to screen millions of pints each year.

"I'm reasonably optimistic that if needed, it could be done," said Dr. Jesse Goodman, deputy director of the Center for Biologics, Evaluation and Research at the FDA.

He suggested that an early test could be used to screen blood going to patients who are particularly susceptible to West Nile. The FDA could allow use of the test as an experimental product before it is officially proven effective and licensed. That, he said, could give the blood supply some quick added protection.

Others are less confident.

"It's going to take several years to have a test suitable for blood donors," said Dr. Harvey G. Klein, chief of the Department of Transfusion Medicine at the National Institutes of Health and past president of the American Association of Blood Banks.

The tests, he said, are very early in their development. "Prior to the appearance of West Nile in this country there was certainly no reason for U.S. manufacturers to develop a screening test."

He said that tests available today would produce some false positives, where healthy blood appears to be infected. Using these test could mean throwing away many pints of good blood at a time when the blood supply barely keeps up with demand.

West Nile is now diagnosed in patients using an antibody test, which looks for signs in the blood that the body is fighting off the disease.

That test cannot be used to screen donated blood because the virus lingers in the blood for at least a few days -- maybe as long as two weeks -- before a patient develops symptoms and detectable antibodies, which the body produces to fight off disease. Officials are worried about people who donate blood before they know they are sick.

Further, people with West Nile do not always get sick. Just one in 150 people with the virus gets severely ill with a potentially fatal brain inflammation. An estimated 30 in 150 people will get minor symptoms.

More promising, experts say, is a test that looks for the virus itself in the blood. Nucleic acid tests look for genetic material that is present in the blood and have already been successfully licensed to screen blood for HIV and hepatitis C.

But it will be difficult to transform this sort of test into reliable mass production.

"There are many challenges in taking something that works in a lab and moving it into the field," Goodman said. "Those are challenges that can be met if needed, but they are substantial."

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On the Net:

Food and Drug Administration background: http://www.fda.gov/cber/safety/westnile.htm

Centers for Disease Control and Prevention background: http://www.cdc.gov/ncidod/dvbid/westnile/index.htm