Gen-Probe and Chiron announced that the pivotal clinical trial of the companies' Procleix West Nile virus (WNV) blood screening Assay has been initiated.

The companies also noted that since the start of this year's mosquito season in May, ongoing screening of the US blood supply with the Procleix WNV Assay, labelled for investigational-use only, has detected 20 WNV-infected donations to date, thereby preventing transfusion of virally contaminated blood into as many as 60 blood recipients. Since July of 2003, the Procleix WNV Assay has been used nationwide to screen the US blood supply for WNV under an investigational new drug application, or IND, the company release says.

"West Nile virus continues to increase as a health concern as the virus spreads across the United States," said Andrew Heaton, vice president and chief medical officer, Chiron Blood Testing. "Chiron is committed to increasing the safety of the blood supply, and we are hopeful that the Procleix WNV Assay will be an important advance in addressing this new health threat," he stated.

"Beginning this pivotal trial on schedule and in time for the peak mosquito season is another important milestone in what has been a remarkably rapid development program to address an emergent health-care concern," said Jim Godsey, Gen-Probe's executive vice president of development. He added, "We remain on track with plans to file a Biologics License Application, or BLA, to commercialize the West Nile virus Assay in the first quarter of 2005."

The pivotal clinical trial, which is being conducted at five US blood centres, will evaluate the Procleix WNV Assay's sensitivity, specificity and reproducibility on the semi-automated instrumentation platform called eSAS. Blood will be tested in pools of 16 and individually in the trial, which is expected to last approximately four months.

Gen-Probe and Chiron expect to begin IND testing of the Procleix WNV Assay in August on the fully automated, high-throughput Tigris amplified nucleic acid testing (NAT) instrument. The Tigris system is expected to increase the efficiency of testing individual blood donations. Testing individual donations enables more sensitive detection of WNV, which is often present only in small numbers in blood.

WNV is a mosquito-borne virus associated with a human form of the disease ranging from mild, flu-like symptoms to severe neurological disease. The first confirmed US death resulting from transmission through donated blood was reported in 2002. According to the US Centres for Disease Control and Prevention, 108 human cases of WNV infection have been reported for the current mosquito season as of July 13, 2004.

Procleix Assays and Systems incorporate NAT technology to detect viral RNA and DNA in donated blood and plasma during the very early stages of infection, when those infectious agents are present but cannot be detected by immunodiagnostic tests.

The Procleix HIV-1/HCV Assay, developed in collaboration with Gen-Probe Incorporated, has been commercially available in Europe since 1999 and also bears the CE Mark.