An uptick in dead birds testing positive for West Nile virus this summer prompted the region’s mosquito control agency to spray some Sacramento neighborhoods with pesticides on Monday and Tuesday nights.
The Sacramento-Yolo Mosquito and Vector Control District conducted aerial spraying over a large chunk of south Sacramento stretching from Broadway on the north, Meadowview Road on the south, Interstate 5 on the west and Power Inn Road on the east. It was the first time the district had conducted such spraying in urban areas since 2012.
Beginning last week, the district collected 38 dead birds and 57 mosquito samples testing positive for the disease in the area targeted for spraying.
“Once the mosquitoes are flying adults and we know they’re infected, the best way to reduce their abundance is aerial spraying, especially when we know it’s over a large area,” said district spokeswoman Luz Rodriguez.
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West Nile virus is commonly transmitted from mosquitoes to vertebrates, such as birds and humans, from which mosquitoes get their “blood meal.”
This summer’s West Nile season is milder than the one in 2012, when the district received reports of infected birds and mosquitoes as early as May. But analysts said they rank this season as more intense than last summer, when no aerial spraying was used in urban areas.
At this time last year, California health officials had found 124 mosquitoes statewide testing positive for West Nile, compared with 234 positive samples so far in 2014, according to the California Department of Public Health.
Bill Reisen, adjunct professor at the Center for Vectorborne Diseases at University of California, Davis, said the district has been “proactive” in managing West Nile in this part of the state, where the summer heat facilitates the virus’s replication and transmission.
Experts often look at the number of birds infected by West Nile as a signal of the virus’s prevalence in a given region.
Besides spraying, the district uses other strategies throughout the year to control the mosquito population. They include treating standing water in public areas with pesticides and distributing mosquito-eating fish to residents.
The district ramped up its control efforts following a major outbreak in 2005, when Sacramento County was the state’s epicenter of West Nile virus two years after it reportedly arrived in California. That year, there were 880 human cases of West Nile statewide, 19 of which were fatal, according to the California West Nile virus website, which is maintained by state agencies and UC Davis.
Only two human cases of West Nile virus have been reported this year: in Contra Costa and San Joaquin counties.
Blake Isaacs, a 28-year resident of Sacramento’s Land Park neighborhood, one of the communities sprayed in the last two days, was one of the county’s 177 human cases of West Nile in 2005. Because of the virus’s novelty to the region, it took a year of febrile symptoms before he was properly diagnosed.
Monday night, Isaacs and his wife carefully followed the district’s live update of the first aerial spraying. By around 9:30 p.m., when the spraying was scheduled to start, they closed their windows and brought their pets into their house.
“No one likes the pesticides being administered, but we understand why it’s necessary,” said Jackie Isaacs, his wife.
“If it makes people more comfortable to stay inside and close their doors, then they can, but we don’t make any specific recommendations for the spraying,” said Rodriguez, adding that the cocktail of pesticides was deemed safe by the U.S. Environmental Protection Agency and the California Department of Pesticide Regulation.
Although a study published on June 22 by the UC Davis MIND Institute linked a 60 percent increased risk of autism in children of women exposed to organophosphates, a general class of chemicals frequently used in pesticides, the study’s principal investigator, Irva Hertz-Picciotto said their study did not examine the effects of the specific organophosphate pesticide the district used in its spraying, called naled.
“Just because it’s an organophosphate doesn’t mean I can say that it’s going to have much effect,” Hertz-Picciotto said. “I can’t say that it’s safe, but I can’t say how much risk there is, either.”
The district has no additional spraying planned, but Rodriguez said it will continue to be on the lookout for West Nile activity for the remainder of the summer months. Experts say transmission peaks between July and September.