Diagnostics & Imaging Week

The ‘Governator,” Arnold Schwarzenegger, last week declared a state of emergency to prevent the spread of West Nile Virus in Colusa, Kern, San Joaquin and Glenn Counties in his state. Eight deaths have been reported this year in California, primarily in those counties, due to WNV.

About the same time, a man in Cobb County, just west of Atlanta, Georgia, and three birds tested positive for WNV, according to a report issued by the Georgia Public Health Laboratory.

The conclusion: WVN is here in the U.S. — all over the U.S.

In response to this threat, FDA reported that it has approved a second test for the detection of West Nile Virus — this one from Roche Diagnostics (Pleasanton, California) — in donated human blood and plasma, which will join its competitor, Gen-Probe (San Diego) in this market.

Although West Nile Virus is transmitted primarily through mosquito bites, it can also be transmitted like other infectious diseases through infected blood, blood products or organ transplantation from infected donors.

Meanwhile, the FDA also said that it approved the test as the agency is preparing guidance on the use of licensed WNV screening tests for blood donors.

The company said that the diagnostic, called the cobas TaqScreen West Nile Virus test, enables detection of the virus “earlier in the infection cycle in donors who may show no symptoms of disease.”

Chris Parkhouse, international business leader, blood screening, for Roche Molecular Diagnostics, told Diagnostics & Imaging Week that the cobas TaqScreen test utilizes different technology than its competitor in this sector.

“Our test is PCR — polymerase chain reaction – and it is directed against the flavivirus family, which includes West Nile Virus. But it will also detect St. Louis Virus, Japanese encephalitis, Murray Valley [encephalitis virus] and one or two other viruses that have been shown to cause transfusion-transmitted infections,” Parkhouse said.

“The other licensed assay” from Gen-Probe uses “transcription-mediated amplification” technology, Parkhouse said.

The development of this “broad spectrum” assay, he said, “stems back to early discussions with the FDA in 2003, when the agency pulled together manufacturers” to determine if they could produce such a test.

For example, he said, St. Louis virus encephalitis is “associated with periodic outbreaks in the U.S.”

The FDA said that while WNV infection is “common” in Africa, Asia and the Middle East, the U.S. was not impacted by the disease until 1999, when it first appeared in this country. Since then, the agency said, WNV has become “endemic” in most of the U.S., with from 1 million to 3 million cases between 1999 and 2006, according to the Centers for Disease Control and Prevention (CDC; Atlanta).

In a statement, Jesse Goodman, MD, director of FDA’s Center for Biologics Evaluation and Research, said, “This action is the culmination of the dedicated efforts of FDA, our sister agencies, blood establishments and manufacturers to bring donor screening tests to market for this increasingly common virus.

Roche’s test is approved for the detection of the virus in plasma specimens from human donors of whole blood and blood components and living donors of cells, reproductive cells and other tissues. The FDA said it is also intended for use in testing plasma specimens of organ donors when specimens are obtained “while the donor’s heart is still beating.”

As a result, Goodman said, “blood centers and hospitals now have a choice of two FDA-approved tests” to screen for WNV in donated blood and organs.

While most people infected with WNV show no symptoms of the disease, the FDA said about 1 in 150 to 1 in 350 infected people will develop serious symptoms, including encephalitis, or inflammation of the brain.

“WNV has been especially virulent this year,” the FDA said. “Although it is still early in the WNV season, 58 blood donors who are possibly positive for the virus have been reported to the CDC as of August 21, 2007.”

Since the introduction of the virus, the reported number of human cases of serious WNV in the U.S. “has grown steadily” from 62 in 1999 to 4,269 in 2006.

Now that there are two licensed tests, still — according to Parkhouse — WNV testing is not mandated in the U.S. It is expected that this new guidance, once it is issued, will essentially mandate WNV testing.

Karen Riley, a spokeswoman for FDA, told D&IW that the guidance has not yet been released, but that its content of it has been discussed recently at several Blood Product Advisory Committee meetings.

Riley said that there is no specific time-frame in which the FDA will issue the guidance on the use of licensed WNV screening tests for blood donors.

Gen-Probe received its first approval for a blood screening assay in late 2005, although at that time, U.S. blood centers had used Gen-Probe’s Procleix WNV assay to screen more than 29 million units of donated blood since 2003.

At the time, Henry Nordhoff, chairman, president/CEO, of Gen-Probe, said, “FDA approval of our West Nile virus assay represents another significant milestone in our efforts to help safeguard the U.S. blood supply with our innovative nucleic acid testing technologies.”

Earlier this year, Gen-Probe’s Procleix Tigris automated system also was cleared for WNV blood screening.