By NEALE MULLIGAN
Stanford Blood Center is the first in the Bay Area to offer on-site screening for the West Nile virus. Using a new set of analytical tools from Roche Diagnostics, the screening process will help prevent the spread of the potentially deadly virus through the transfusion of blood and blood products.
In the past, blood centers have relied upon antibody tests to detect infectious agents.
"The problem with the antibody tests is that there is a delay between when you’re exposed to an agent and when your body makes antibodies of sufficient quantity that we are able to find it with an antibody detection test," said Susan Galel, MD, associate professor of pathology at the School of Medicine and associate medical director of the center.
The delay is significant. Scientists believe antibodies are produced 10 days to two weeks after infection. This new screening approach, called a nucleic acid test, is designed to find genes of the West Nile virus, which are detectable before antibodies are produced.
With the West Nile infection, individuals are infectious only before they have produced antibodies, which is different from other infectious agents such as HIV and hepatitis C. Patients with HIV and hepatitis C produce antibodies to fight the infection as the virus continues to circulate.
The West Nile virus, however, has no chronic carrier stage. "You’re infectious just for that initial period of time when the virus is circulating. Once you make antibodies the virus is cleared from your blood and the donor is no longer infectious," said Galel. "We only need to screen blood donors for that initial peak of infectivity and the only test that will detect that is the nucleic acid test."
An estimated 20 percent of people with the West Nile virus develop symptoms that are similar to a flu-like illness. Less than 1 percent develop more serious conditions that affect the nervous system, such as meningitis, encephalitis or muscle weakness that can be fatal.
According to the U.S. Centers for Disease Control and Prevention, the mosquito-borne virus killed 284 people in the United States last year. To date, one U.S. case of human West Nile virus infection has been reported in 2003.
"It may be that over time, this virus might burn itself out because people will develop an immunity," said Galel.
There is no evidence that the West Nile virus spreads from person to person other than through blood transfusion, organ transplantation and breastfeeding.
"It’s important to clarify that the test we will be using is an investigational test. However, there is good scientific reason to believe that we will improve the safety of the blood supply," Galel said.
Stanford Report, July 9, 2003