August 27, 2013
1 min read

West Nile virus continues to evolve

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As officials in Texas warn residents about increasing numbers of West Nile virus infections in the state this year — there were 21 as of Aug. 27 — study data published online shed some light on how the virus has evolved in Houston during the past decade and suggest that strains circulating in Houston in the past 3 years may be derived from strains circulating elsewhere rather than those that had been previously circulating in the area.

Alan D.T. Barrett, PhD, director of the Sealy Center for Vaccine Development and professor in the departments of pathology, and microbiology and immunology at the University of Texas Medical Branch in Galveston, and colleagues used surveillance data from the Houston area and conducted genomic sequencing of 14 West Nile virus isolates collected from 2010 to 2012 from resident birds.

“Inferred monophyletic relationships of these groups with several 2006-2009 northeastern United States isolates supports potential introduction of a novel West Nile virus strain in Texas since 2010,” the researchers wrote in a recent issue of Emerging Infectious Diseases.

Study limitations, according to the researchers, include “poor statistical confidence for all inferred basal node topologies within the NA/WN02 genotype limits direct comparison of independent evolution between Harris County isolates in different monophyletic lineages.”

In addition, the researchers noted the potential for sampling bias.

Regardless, the findings highlight a need to “to maintain West Nile virus surveillance activities to better understand West Nile virus transmission dynamics in the United States,” the investigators said.

Health officials in Texas are reminding clinicians to counsel patients about reducing the risk of exposure to West Nile virus, by eliminating standing water and other mosquito-breeding areas; making sure door, porch and window screens are in good condition; and using a repellent that contains DEET, picaridin, oil of lemon eucalyptus or IR3535 when outdoors.

Alan D.T. Barrett, PhD, can be reached at

Disclosure: The researchers report no relevant financial disclosures.