The West Nile virus has made its first reported appearance this year in Arizona, signaling an early start to the season and the threat that human infections could outpace last year’s record numbers.
The positive sample was taken Saturday from a north Mesa fire station on Horne north of McKellips Road, said public health officials. The strong positive result, confirmed by the state Tuesday, leaves no doubt that the virus is circulating from birds to the mosquitoes that bite them, they said. People are likely next in line for infection.
"You’re always concerned when a disease like this pops up earlier than you like," said Doug Campos-Outcalt, Maricopa County’s interim health officer. "The fear is that we’ll start having human cases earlier and have more of them because the season is earlier, but maybe not."
Public health officials said they cannot predict how bad this year will be for West Nile infections, but having positive test results well before the start of the typical West Nile season gives the virus more time to spread, said John Townsend, Maricopa County’s vector control program manager.
People near where the positive result was found should be especially careful to remove standing water from around their homes and protect themselves from mosquito bites, public health authorities said.
County officials are placing door hangers in nearby neighborhoods with information about preventing the spread of the virus. And tonight, county trucks are scheduled to spray the insecticide Sumithrin between 10 p.m. and 5 a.m. in an area bounded on the north by McDowell Road, on the south by McLellan Road, to the west by Mesa Drive, and one mile east to Stapley Drive.
"There are probably still mosquitoes in the area that have the West Nile virus, so we’re trying to tell people out there we’re fogging because we know there’s a risk to their health and it’s immediate," Campos-Outcalt said.
Last year, the first mosquito sample testing positive for West Nile was in April, followed shortly by a horse testing positive. By May, the first human case was reported.
For most of last year, Arizona led the nation in West Nile cases. Although California eventually surpassed Arizona’s numbers, the state set its own record with 391 human infections and 14 deaths, according to the U.S. Centers for Disease Control and Prevention. Of the total cases, 129 suffered a neuroinvasive disease. Public health officials said they are worried about a repeat of last year because many of those with a neuroinvasive diseases such as meningitis, encephalitis or acute flaccid paralysis still are coping with symptoms from the virus.
"I don’t know that people have quite the respect for the virus that it’s due," said Craig Levy, program manager for the vector-borne disease program at the Arizona Department of Health Services. "It is a potentially life-changing illness for many people."
West Nile authorities also are concerned about the impact wet weather will have on this year’s West Nile virus season. Last year, the state started the season in a drought, with little standing water. This year, rain has left standing water everywhere, perfect breeding sources for mosquitoes, Levy said.
"It’s going to be an even bigger challenge for all counties this year than it was last year," he said.
Maricopa County alone has more than 9,200 square miles that could contain standing water from storm basins, neglected pools, containers around homes and low-lying areas. "Anyone who needs a reality check needs to drive from one side of the county to the other. You realize then that it is impossible to control mosquito" breeding entirely, he said.
What to do: Measures to lessen mosquito breeding and protect against infection:
• Remove standing water in potted plants, tires and other containers around the home
• Repair window and door screens to keep mosquitoes out
• Avoid outdoor activity before dawn and after dusk, when mosquitoes are most active
• Wear long sleeves and pants when outside
• Wear a mosquito repellent with DEET when outside