Dallas Morning News: Study: Mild winter, wet spring to blame for Dallas County’s deadly West Nile outbreak

A plane flew over central Dallas as part of aerial spraying efforts last summer to combat mosquitoes carrying the West Nile virus. (Credit: Dallas Morning News)

A plane flew over central Dallas as part of aerial spraying efforts last summer to combat mosquitoes carrying the West Nile virus. (Credit: Dallas Morning News)

The Dallas Morning News covered the research of SMU economist Thomas B. Fomby and SMU Dedman College Distinguished Alumnus Robert W. Haley, who co-authored a new study on West Nile Virus.

Fomby and Haley, along with other researchers, analyzed a decade of data related to West Nile Virus and, in particular, the 2012 West Nile epidemic in Dallas County. The analysis allowed them to identify important precursors of West Nile Virus outbreaks that allow for early and effective intervention.

Fomby, a data modeling expert, is a professor of Economics and director of the Richard B. Johnson Center for Economic Studies at SMU.

Haley is chief of Epidemiology and professor of Internal Medicine at UT Southwestern. Other authors of the study were physician Wendy Chung, chief epidemiologist, and her associates Christen Buseman, Sibeso Joyner and Sonya Hughes, all of Dallas County Health and Human Services; and James Luby, professor of internal medicine in the Division of Infectious Diseases at UT Southwestern.

They reported the findings in the July 17 issue of The Journal of the American Medical Association.

Their analysis of the West Nile data, along with weather and housing data, found that the epidemics begin early, after unusually warm winters; are often in similar geographical locations; and are predicted by an index based on an estimate of the average number of West Nile virus-infected mosquitoes collected per trap-night, called the Mosquito Vector Index.

As a result of their data analysis, the researchers recommend the use of a vector-index rating system to identify the best timing and location of early interventions.

Read the full story.

EXCERPT:
By Sherry Jacobson
Dallas Morning News

An in-depth study of last year’s West Nile epidemic in Dallas County blames a mild winter, wet spring and an abundance of mosquitoes for spreading the sometimes-fatal virus.

But local officials did not realize how quickly the mosquito-borne outbreak was unfolding. If they had recognized the signs earlier, 110 severe human infections might have been prevented and a dozen lives saved, the study said.

“It’s a very optimistic estimate and might not be totally realistic,” said Dr. Robert Haley, one of the authors of the study published Wednesday in the Journal of the American Medical Association.

His estimate was based on the possibility that officials could have resorted to aerial spraying of insecticides in early July, instead of a month later. It also supposed that spraying could have halted the West Nile outbreak.

The study suggested a deadly equation was at work: Five percent of the Culex mosquitoes were carrying the West Nile virus by late June. At that point, the disease was spreading quickly, but no one knew it.

While the conclusions are purely hindsight, the study could provide valuable information to help prevent future West Nile outbreaks, said Haley, chief epidemiologist at UT Southwestern Medical Center.

“This could be a breakthrough for how to track a West Nile outbreak,” he said. “For a small amount of data, this study is remarkably strong.”

The study grew out of the worst West Nile outbreak in Texas history. More than 400 Dallas County residents suffered mild to severe symptoms of the neuroinvasive disease and 20 died.

All were bitten by infected mosquitoes despite widespread warnings and ground spraying of insecticide. But no one could explain why it happened.

Dr. Wendy Chung, the study’s lead author, said researchers looked for answers in a massive amount of West Nile data collected last year by government agencies.

The study focused on infected mosquitoes and how quickly they passed the virus to humans. It also considered the locations where people were infected and if weather patterns might have accelerated the outbreak.

“Weather that predisposes us to have a bad West Nile season is considered one of the soft indicators” of an impending outbreak, said Chung, chief epidemiologist for Dallas County Health and Human Services. “You can have bad weather and not have a bad season.”

Read the full story.

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