Last updateTue, 17 Oct 2017 5pm


Rise in infected mosquitoes triggers local fogging

Courtesy of the Santa Clara County Vector Control District
Areas of Los Altos, Mountain View and Sunnyvale, in green, were scheduled to undergo fogging this week to stop the spread of West Nile virus.

The bite of summer’s notorious insect – the mosquito – is potentially packing a bigger punch this year. Mosquitoes infected with West Nile virus have popped up in the area, prompting the Santa Clara County Vector Control District to take steps to prevent the transmission from insect to human.

After responding to the report of a dead crow, a bird prone to West Nile virus, near the intersection of Fremont and Mary avenues in Sunnyvale, district officials confirmed the presence of the virus in mosquitoes at collection sites in Los Altos, Mountain View and Sunnyvale last week. The district authorized an Ultra Low Volume fogging of insecticides Tuesday – after the Town Crier’s deadline – over a 1-mile radius that included parts of Los Altos and Mountain View.

Due to the sharp increase in infected birds, this was the district’s sixth fogging this year and the first in Los Altos.

“We try to avoid reaching this stage,” said Jose Colome, community resources specialist for the district. “We are having high activity locally.”

A follow-up round of mosquito testing is scheduled this week to determine the effectiveness of the fogging. If the tested mosquitoes prove negative for the virus, Colome said the district would not schedule additional fogging in the area – unless more infected crows are discovered.

To date, 175 dead birds have tested positive for West Nile virus in the district this year, or approximately 72.3 percent of all dead birds tested by the vector control district. That’s abnormally high, according to Colome, especially with mosquito season just beginning. The numbers increase the chances of people becoming infected from a mosquito bite.

“When we have mosquitoes testing positive for the virus, risk of transmission to humans is imminent,” Colome said.

While most people infected with the virus experience no symptoms, the state of California reports that one out of every 150 infected individuals suffers from symptoms ranging from fevers to headaches, comas, vision loss and paralysis. Of the 433 human cases last year, 15 proved fatal.

Preventive procedures

Some residents fear that the microscopic dosage of insecticide applied during the fogging may be more dangerous than an infection from the virus. Colome reassured residents that the treatment is safe and the method approved by the California Department of Public Health. He added that residents can safely eat fruits and vegetables from their yards the day after the fogging.

“Lacking vector control activity in an area can be giving free range for the replication of the disease in mosquitoes,” said Colome, who noted that an area of Dallas that refused to fog in 2012 suffered an outbreak of the virus that led to 18 deaths and the need for a more toxic fumigation.

Following normal preventive procedures, district technicians have been combatting larvae on public and private properties with low toxicity biorational treatments and naturally occurring bacteria. To clear stagnant water, the prime breeding ground for mosquito larvae, district workers have identified swimming pools that require maintenance based on aerial survey.

Despite the district’s efforts, Santa Clara County has reported more cases of infected birds than any other in California. Colome said 43 of the 70 infected birds reported to the state last week were found in this county.

“A hypothesis is that birds and humans share the same sources of water,” Colome said of the high rates locally. “Most are the result of domestic irrigation, swimming pools and lawn water use. … That’s why it’s so important to stress preventive measures.”

For more information, visit sccgov.org/sites/vector.

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