Vector index can stave off West Nile virus.

• Position: Your Life - Brief article

West Nile infections in humans can cause long-term neurological damage and even death. An investigation at the University of Texas Southwestern Medical Center of the nation's largest West Nile outbreak--which occurred in 2012 in Dallas County--revealed that the best way to avoid an outbreak and stave off the resultant rise in human infections was to determine the mosquito vector index. It is calculated from the percentage of mosquitoes infected with West Nile virus.

"When the vector index goes above 0.5 early--in June or July--large numbers of people are silently infected, and this is the best time to intervene," advises Robert Haley, chief of epidemiology and professor of internal medicine. "In years when the vector index did not rise until late July or August, impending outbreaks just sputtered. In late summer, mosquito abundance declines, and mosquitoes become less active and stop biting as much."

The study also showed that determining the number of West Nile virus infections in people is a poor way to...