Originally Published IVD Technology
May 2003
INDUSTRY NEWS
WNV tests near completion |
At the start of 2003, threats of biowarfare attacks captured the attention of the press, the medical industry, and U.S. residents. In March, word of the new and sometimes deadly severe acute respiratory syndrome (SARS) epidemic flooded the headlines. All the while, one of North America’s most virulent diseases lay in wait to make a repeat performance this summer.
Although less than 1% of infected people develop serious symptoms, when West Nile Virus (WNV) leads to encephalitis, severe, and even lethal, swelling of the brain can occur. The virus is transmitted predominantly by bites from infected mosquitoes. The disease can survive, even through a long winter, in dormant larvae.
Between the onset of mosquito season and April 15, 2003, 4156 cases including 284 deaths from WNV were reported in the United States alone. In 2002, the virus also spread into Canada.
Last year, at least 21 of the more than 4000 people infected with WNV in the United States contracted the disease via blood transfusions or organ transplants. Approximately 80% of infected people do not develop any symptoms, and would be eligible to donate blood, so a test is sorely needed.
However, WNV has a very low viral yield, and current testing techniques do not have sufficient sensitivity or specificity to detect it in donated blood during early stages of infection.
The American Association of Blood Banks (Bethesda, MD) expects to have a test capable of screening donated blood for WNV ready for distribution by July 1, 2003.
IVD companies have worked diligently through the winter and spring to meet this goal and develop tests that will ensure the safety of the blood supply from contamination by WNV in the United States and Canada.
Several tests are in development. Chiron (Emeryville, CA) and Gen-Probe (San Diego) have partnered to develop one test and Roche Biomedical (Burlington, NC) is developing another. Both tests use nucleic acid amplification testing (NAT) to detect the viral RNA in the blood.
NAT allows for significantly earlier detection of WNV infection than the current testing method, which uses immunoglobulin (IgM) antibodies to detect WNV. Traditional testing methods are not suitable for screening donated blood, because they require that antibodies or viral proteins reach detectable levels in the body. These WNV tests in development facilitate earlier detection by incorporating methods for the extraction, amplification, and detection of low levels of viral RNA from donated blood.
FDA has called for a sensitivity standard of 100 copies/ ml for an individual donation. NAT heightens diagnostic sensitivity, often at the cost of specificity. Therefore, an appropriate confirmatory test, likely to be based on an IgM-testing platform, may be needed.
Gen-Probe’s test was granted investigational new drug (IND) status in March, allowing blood banks to use it for screening donated blood. The test was funded, primarily, by a $3.47 million grant from the National Heart, Lung, and Blood Institute.
The test is based on Gen-Probe’s Transcription-Mediated Amplification (TMA) technological platform along with Chiron’s Procleix semiautomated instrumentation. The same technological platform and instrumentation form the basis of Gen-Probe’s currently approved HIV-1/HCV test. The company is also developing a system using its fully automated TIGRIS instrumentation platform. Gen-Probe has said that its test has greater sensitivity than the Centers for Disease Control and Prevention’s Taqman panel.
In April, the American Red Cross began a Phase I preclinical study of the assay with a banked blood prevalence study. Results of this study should provide information about the potential prevalence of the virus, based on banked blood gathered during last year’s epidemic. After the prevalence study, Gen-Probe plans to submit a prospective clinical protocol amendment to the IND application, and initiate a Phase II study on the current blood donor population. The company expects to have its test ready to be distributed to blood banks by July 1. Chiron will market and distribute the test.
Chiron is developing an alternative NAT. The company is cloning a genetically engineered, noninfectious WNV genome that could be used as a NAT standard to confirm testing for the Procleix TMA IND. The test may also be used to evaluate NAT tests undergoing Phase II testing this summer.
Roche’s test, the TaqScreen WNV System, is based on the company’s polymerase-chain-reaction (PCR) technology. The real-time PCR test incorporates the Hamilton MicroLab AT/plus 2 Pipettor along with the COBAS AmpliPrep and Taqman Analyzer into one system to screen whole blood for WNV.
The company has begun to install its blood-screening systems in preparation for clinical trials, scheduled to begin by July 1. Systems have been installed at two of the America’s Blood Centers testing sites in the United States and at both Canadian Blood Services and Hema Quebec testing sites in Canada.
The National Genetics Institute (Los Angeles) and Tetracore (Gaithersburg, MD) are also developing NAT-based blood-screening tests for WNV.
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