West Nile Virus – A 2023 Perspective

With all the other infectious diseases in the news, we haven’t heard a lot about West Nile Virus (WNV) this year.  WNV was first documented in the United States in 1999.  It is a mosquito-borne virus, but transfusion transmission was noted in 2002.  A test for research use was implemented in 2003 for all donors in the United States to try and prevent transfusion transmission, with FDA licensure occurring in 2005.  It has been largely successful, with only rare cases still occurring because of a lack of sensitivity with the assay.

The screening test for WNV for blood donors is a nucleic acid amplification test (NAT) which looks for viral RNA.  Our testing lab is currently using the Procleix® assay on the Panther system, tested on pools of 16 donor samples. If an increase in WNV activity is noted in an area, based on surveillance of donor and patient cases, testing switches to individual sample tubes, rather than pools of samples, to increase sensitivity.

Fortunately, the impact of WNV on the community blood supply, at least in our area, has been small in 2023.  Carter BloodCare has had only three donors screen positive for WNV in 2023, and all of those were within a five day span in mid-August; two were in Denton County and one was in Dallas County.  Texoma Blood Center to our north, in Sherman, Texas, had one donor test positive for WNV all year to date.  The Texas Department of State Health Services lists 27 presumptive viremic blood donors for the entire state as of October 24, 2023.

In 2022 Carter BloodCare also saw three donors test positive, but later in the year – mid-October through early November.  Here is a table of our past WNV donor positives since testing began in 2003:

Positive Cases WNV over the years

The worst year in our area was clearly 2012, with 72 positive donors.  An article was published in the journal Emerging Infectious Diseases in 2015 discusses the 2012 outbreak in DFW.   Obviously, some years have several cases of WNV activity in the donor population and others have little to none. This variability could be explained by current levels of immunity in the population, how much time we spend outside (uptick in 2020 during the first year of COVID?), attention to using mosquito repellent and changes in weather cycles.  But WNV clearly persists and so we must continue to test as a donor center and be vigilant as individuals.

Additional reading:

Hayes C, Stephens L, Fridey JL et al.  Probable transfusion transmission of West Nile virus from an apheresis platelet that screened non-reactive by individual donor-nucleic acid testing.  Transfusion 2020, 60:424-429.