West Nile Virus — a potentially deadly infection spread by mosquito bites — is now a permanent resident of Arizona, according to a study by Northern Arizona University (NAU) and the Translational Genomics Research Institute (TGen), an affiliate of City of Hope.
Originally isolated in 1937 in the West Nile district of Uganda, Africa, the first Arizona case appeared in 2003, four years after it first emerged in the United States, most likely from bird migrations. The NAU-TGen study results suggest that Arizona’s moderate temperatures allow the West Nile Virus (WNV) to survive throughout the winter in the Grand Canyon State among populations of mosquitoes and birds.
This first-of-its-kind study analyzed the genetic material of WNV directly from mosquitos collected in Arizona to build out a genomic family tree of the virus. NAU and TGen researchers then used advanced computer algorithms to develop a theoretical model of how the virus moves around the American Southwest.
As a result, researchers believe Arizona is a likely permanent source of WNV infection that is annually exported by migratory birds to other states, according to the study, Phylogenetic analysis of West Nile Virus in Maricopa County, Arizona: Evidence for dynamic behavior of strains in two major lineages in the American Southwest, published Nov. 26 in the journal PLOS ONE.
WNV, the leading cause (96 percent) of mosquito-borne disease in the continental United States, was first identified in America in New York in 1999. It since has spread to every state but Hawaii, causing more than 1,000 deaths. It usually is active in the summer and fall, dissipating when temperatures reach freezing, something that rarely happens in central Arizona’s Maricopa County.
In fact, using this sophisticated genomic analysis, researchers identified two dominant strains of WNV — NA/WN02, and SW/WN03 — which have circulated in Maricopa County for approximately four and seven years, respectively.
“This is the first genomic evidence of local over-wintering by WNV strains over the course of several years in Arizona,” said Dr. David Engelthaler, Co-Director of TGen’s Flagstaff-based Pathogen and Microbiome Division, TGen North, and the study’s senior author. “These findings will allow public health officials to better track the virus, allowing for more targeted vector control and public education campaigns.”
WNV samples for this study were collected from mosquitoes trapped weekly at 787 sites throughout the Phoenix metro area by the Maricopa County Environmental Services Department Vector Control Division, which co-authored the study.
Specific West Nile Virus strains were identified using a relatively new protocol called whole genome tiled amplicon sequencing. A version of this protocol was first used to sequence the Zika virus. It was repurposed in this study to sequence WNV by Dr. Crystal Hepp, an Assistant Professor at NAU’s School of Informatics, Computing, and Cyber Systems and the study’s lead author.
“The protocol we created for this study can now be incorporated into routine public health surveillance activities, allowing for better tracking of local viral hotspots, changes in local viral populations and detection of the emergence of new strains of WNV,” Hepp said. “We are currently conducting WNV surveillance across western states to better understand how permanent Arizona viral populations may be a source for continual reintroductions to other regions and other states.”
There are no vaccines to prevent or medications to treat WNV. Fortunately, most people infected with WNV do not feel sick. According to the U.S. Centers for Disease Control and Prevention, about 1 in 5 people who are infected develop a fever and other symptoms, such as headache and nausea. About 1 out of 150 infected people develop a serious, sometimes fatal, illness when the disease spreads to the brain. The CDC recommends reducing the risk of WNV by using insect repellent and wearing long-sleeved shirts and long pants to prevent mosquito bites.
The Pathogen and Microbiome Institute at NAU contributed to this study.