These are the mosquitoes that cause West Nile virus. Here’s how they find them
As concerns grow over reports of intense West Nile virus activity in the Sacramento region, the city of Sacramento Department of Utilities may have unintentionally accelerated a localized increase of West Nile activity in the Pocket area.
The Sacramento-Yolo Mosquito and Vector Control District confirmed that a disruption in water flow from the Pocket Canal to the Sacramento River caused mosquitoes to proliferate in the area. Efforts by the city to apply an algaecide treatment to the Pocket Canal caused the water disruption.
As a result, water backed up into drain inlets in residential areas of the Pocket. The stagnant water within the basins acted as an ideal breeding ground for mosquitoes during West Nile virus season.
With high activity in the area, the district announced Friday it would conduct aerial insecticide spraying Monday and Tuesday in Elk Grove, the Pocket and neighborhoods south of Fruitridge Road.
West Nile virus is a potentially life-threatening disease contracted through the bite of an infected mosquito. Mosquitoes become carriers for the disease after they feed on an infected bird, which acts as a host for the disease.
After residents near the Pocket Canal complained of an odor in the area in past summers, the city determined algae blooms in the canal were the cause. These blooms mostly occur during the summer season, the Department of Utilities explained in a statement.
To combat the odors, the department began treating the canal with an algaecide on June 12.
A State Water Board order, which regulates “discharges of residues from algaecide applications,” permits the city to apply chemical treatments to bodies of water, according to the Utilities Department.
Water is discharged from the Pocket Canal to the Sacramento River via a pump station at the western point of the canal, the department said.
Fernando Dueñas, an associate engineer with the department, explained that officials attempted to control the amount of copper flowing into the Sacramento River from the algaecide treatment.
“To maximize the effectiveness of the algaecide applications, the city shuts down the downstream pumps that discharge into the Sacramento River prior to any chemical treatment,” the statement from the Utilities Department said.
As a result of the city’s decision to turn the pumps off, “water levels in the Pocket Canal were backing up into the storm drain inlets in the surrounding neighborhoods,” the Department of Utilities said.
The water that collects in these inlets is designed to be delivered to creeks and rivers in local areas.
The catch basin crew associated with the Vector Control District checks catch basins and storm drain inlets that catch runoff water from rainfall. The crew found the first inlets full of water on June 27 and started treatment to kill mosquito populations that day.
“Normally, those basins would be dry, and (the crew) noticed that there was water,” said Luz Robles, the public information officer for the Sacramento-Yolo Mosquito and Vector Control District. “They alerted their supervisor and they talked to the city Department of Utilities, so that’s when they figured out there was an issue.”
The basins should be dry, Robles said, because if not, “they’re going to be producing mosquitoes.”
“What the mosquitoes really like, particularly the West Nile vectors, are stagnant bodies of water that are high in organic material,” said Bret Barner, a lab technician with the district, adding that mosquito larvae feed on the organic materials.
One female mosquito can lay 50 to 200 eggs at a time up to two to three times a week. Robles also said heat accelerates the life cycle of mosquitoes.
On June 29, the city received a call from the vector control district over water levels in the canal.
“The Vector Control District informed the city that the storm drain inlets were holding water and creating mosquito breeding habitat,” the Utilities Department’s statement said. “Vector Control also stated that they had confirmed positive samples of West Nile Virus near the canal.”
The city took water quality samples, as required by state permit, before the pumps were turned back on later on June 29.
A second cycle of the algaecide treatment began July 9, and the pump station was again turned off.
“We met with the Vector Control District one week later on the morning of July 16 to inspect the water levels and determined we would need to drain the canal to a lower level before commencing the next round of applications,” the Utilities Department’s statement said. “The pump stations were turned on and the water levels were lowered on July 17.”
Officials from the Utilities Department emphasized their continued collaboration with the vector control district to monitor water levels and prevent water levels from rising in neighborhood drain inlets.
The Pocket area has been identified by the vector control district as an area of concern for West Nile virus, although district officials could not confirm this is due to water flow issues.
“We have the same level of increased activity in Elk Grove as well and they haven’t had the water issues there,” Robles said.
Barner, who has been with the district 4 1/2 years, said the Pocket is not usually an area with high activity. He said residents should be concerned.
“Dress appropriately – long sleeves, long shirts,” he said. “Try to avoid going out at dawn and dusk. Mosquito repellant always helps. (Eliminate) any standing water on your property. The best thing you can do is prevent mosquitoes from being there in the first place.”
The city of Sacramento itself did not alert residents to the increase of West Nile virus activity in the Pocket.
A spokesperson from the city said the vector control district is the agency responsible for informing residents about cases and reports. The district works to inform residents as quickly as possible and the city coordinates with the district to send these alerts.
Robles said she contacts local public information officers for areas with high activity and disseminates information using Nextdoor, an online social network for individual neighborhoods, as well as through city websites and newsletters.
Pocket residents Carole and Henry Sepulveda, who have lived in the area for 33 years, said they discovered their area had high West Nile virus activity after a neighbor posted on Nextdoor. The neighbor had found a dead bird in her backyard that tested positive for the virus.
“I’m kind of surprised (the city) wouldn’t alert the residents so people could be more cautious, particularly with their kids, because kids are more likely to be in and out around outside at dusk,” Carole Sepulveda said. “I would think it would be responsible for them to give some notice to the neighborhood.”
Other locals, like Pocket resident Harry Gibbons, say they’re not overly concerned. But Gibbons also said he wasn’t aware of the notifications sent out by the vector control district about a localized increase.
Recently, the vector control district handed out repellant and informational materials at an event in Seymour Park, in the Pocket area, where numerous mosquito samples – groups of one to 50 mosquitoes – have tested positive for the virus. The district has planned to be present at more community events to inform locals.
“Whenever we can, we want to be here (in the community) and answer any questions face-to-face,” Robles said. “The more you notify ahead of time … once you get to the aerial spraying, if it happens, people won’t be (surprised).”
Sacramento County leads the state for West Nile virus activity. The most recent numbers posted by the vector control district include 67 dead birds and 119 mosquito samples testing positive for the disease in the county. As of July 12, the number of dead birds totaled 26.
Activity has been particularly high in the Pocket/Greenhaven area, Elk Grove and in Sacramento south of Fruitridge Road, leading the district to consider next week’s aerial spray.
“For the last few weeks, the district has been closely monitoring these areas because the number of infected birds and positive mosquito samples has been steadily increasing,” a press release from the district states.
After a decision is made, the district will alert residents as quickly as possible.
The vector control district has been doing ground spraying throughout Yolo and Sacramento counties and testing dead birds and mosquito samples for the virus. Residents can sign up on the district’s website for notifications about spraying activity in their ZIP code.