The West Nile virus (WNV) is a potentially deadly blood borne virus that, while native to Africa, has been introduced into the US within the last two decades.
Now the US Food and Drug Administration (FDA) has announced a new guidance document intended to reduce the potential of the virus being transmitted through the donation of blood, cells, tissue or tissue-based products.
Such donations are already regularly screened for a wide array of viruses, including HIV (Types 1 and 2), hepatitis B and C, the human T-lymphotropic virus.
As of 2003, the required testing battery also includes ones to detect WNV, which was first observed in the US in 1999 and by 2002 had already reached epidemic levels. Since then several nucleic acid tests (NATs) have been developed, which have mostly helped to ensure that the blood supply is safe from potential incidents. According to the Red Cross, there have been just 11 documented cases of transmission. FDA meanwhile cites research showing 12 documented cases.
These transmissions, though, haven't been attributed to human error or lack of effort. According to the Red Cross and FDA, these infections are occurring because of "very low viral loads," which can trigger infections in patients who are immune-compromised or otherwise susceptible to infection.
It's those very same viral loads that have worried regulators and other public health officials. The currently approved assays have limits to their ability to detect the virus, meaning that even doing repeated confirmatory testing can create a false sense of security.
"Data have shown that up to 10% of blood donors who have a reactive ID-NAT that fails to be reactive on repeat testing … actually are infected, based on the presence of antibodies to WNV either in the index donation (approximately 8%) or on a follow-up test (approximately 2%)," FDA explains in its guidance.
On 24 October 2013, FDA releasedDraft Guidance for Industry: Use of Nucleic Acid Tests to Reduce the Risk of Transmission of West Nile Virus from Donors of Human Cells, Tissues, and Cellular and Tissue-Based Products (HCT/Ps), which calls on the donation industry to utilize FDA-licensed donor screening assays when screening donated HCT/P products.
Because screening tests can potentially be brought to market as lab-developed tests (LDTs), which are not presently regulated by FDA, the requirements could be seen as an attempt to make sure test results were validated by accurate equipment.
In addition, the guidance specifically recommends the use of an individual-not mini-pooled-NAT screening procedure that has been licensed for use by FDA. Any donor whose HCT/P product test is positive or reactive to WMV is ineligible to donate.
The use of an individual NAT is hoped to reduce the potential for a pooled blood product to contain the virus.
The draft replaces an earlier document by the same name released in April 2008 (73 FR 22958). Comments on the guidance are due by 22 January 2014.
Draft Guidance for Industry: Use of Nucleic Acid Tests to Reduce the Risk of Transmission of West Nile Virus from Donors of Human Cells, Tissues, and Cellular and Tissue-Based Products (HCT/Ps)