Willow Glen Resident

News

West Nile virus found earlier than expected

By Monica Heger

The onset of summer brings more than just warm summer nights, barbecues and fun in the sun. The change of seasons also brings mosquitoes, some carrying the West Nile virus.

The Santa Clara County Vector Control District found the first West Nile virus-positive mosquitoes in West San Jose near Johnson Avenue and Prospect Road.

According to Kriss Costa, community resource specialist for the district, the findings came earlier in the summer than usual. She said mosquitoes don't usually start testing positive for the virus until late August or early September.

"All the water we had and the warm humid weather really kicked off the mosquito activity," Costa said.

The district was been concerned about the growing threat of West Nile virus in Santa Clara County for some time. A mail-in ballot was sent to property owners last May, asking voters to approve a property-assessment hike. It passed, raising an additional $4 million annually.

Costa said the entire amount has gone toward thwarting West Nile.

"We predicted there would be a big increase with West Nile," Costa said. "We watched as it moved through the U.S., so we knew it would take a lot more resources than it has in the past--more staff, products and outreach."

So far, she said the district has found two groups of positive mosquitoes, both in the West San Jose area. The district has also found 14 dead birds in the county that have all tested positive for the virus.

"We'll be keeping an eye on the surrounding area," Costa said. "The way the virus moves, it looks like it came from the south area of Santa Clara County."

Last year, Willow Glen had an unusually high number of West Nile cases. Costa said it was too early to predict if that would reoccur this year.

Costa advises residents to wear mosquito repellent, pants and long sleeves in the evening and to get rid of any standing water. She also said to inform the district of any mosquito problems, dead birds or standing water.

"We need to know where there are mosquito issues, and we need to know early," she said. "If we can take care of the mosquitoes in their aquatic stages, we're a lot better off than waiting until their adult stages."

Costa said dead crows, hawks or other birds could be an indication of West Nile, and residents should contact vector control. The area where the positive mosquitoes were found was fogged with Pyrenone 25-5, a chemical made from chrysanthemums. According to Dr. Noor Tietze with the vector control district, the chemical is not dangerous to humans.

The spraying was done at night, because ultraviolet rays from the sun break the chemical down.

"When the sun comes out the next day, it will be gone in a matter of an hour," Tietze said.

Pyrenone is effective against mosquitoes because they lack the necessary enzymes to break down the molecule.

Tietze said Pyrenone is not the most commonly used spray for mosquitoes, but unlike other sprays that target mosquito larvae, Pyrenone targets adult insects.

Tietze said he prefers using chemicals that target mosquitoes in their larval stage because there is less impact on other insects. The one he prefers is made from spores from the bacteria Bacillus that are toxic to mosquitoes.

"I prefer using Bacillus whenever I can because it has low non-target impacts," Tietze said. "It won't affect beetles and works well to keep other insect predators alive, while targeting mosquito larvae."

A natural form of mosquito control is with mosquitofish. These fish are natural predators of mosquito larvae and are recommended for use in standing bodies of water--such as animal troughs and ornamental ponds. Residents can acquire them for free from the vector control district. However, residents are not allowed to introduce them to natural environments. Tietze said they are most likely already found in most bodies of water in the area.