City of San Jose

Announcement for August 30th:

There will be a meeting regarding West Nile Virus Insecticide Spraying
tonight (Tuesday Aug. 30th) at 6:30 p.m. at the
South Side Community Center,
5585 Cottle Rd. San Jose
Visit this link for more information

West Nile Virus Background

The West Nile virus (WNV) is transmitted by a mosquito vector and can result in encephalitis in infected humans and equine. WNV can also result in wild and domestic bird mortality. WNV was first discovered in a woman from the West Nile District of Uganda in 1937. WNV spread across areas of Africa, Eastern Europe, West Asia, and the Middle East, eventually appearing in the Eastern United States in 1999.

West Nile Virus and Your Health

The West Nile virus (WNV) belongs to the Flaviviridae family (genus Flavivirus) and is part of the Japanese Encephalitis (JE) serocomplex. JE viruses are maintained in nature by a mosquito vector and bird reservoir host. Humans and other mammals infected with WNV are considered "dead-end" hosts, as they are not expected to contribute to the transmission cycle. Although the exact origin of the WNV found in the U.S. remains unknown, the strain isolated from the 1999 outbreak is most closely related to that isolated in Israel in 1998 from a dead goose.

Approximately 20% of persons infected with WNV develop West Nile fever, presenting with flu-like symptoms, mild fever, headache, and body ache. Skin rash and swollen lymph glands may also accompany infection. Symptoms of WNV in humans generally appear within 3-14 days of infection, following a period of incubation. Some individuals who become infected with the virus (less than 1%) develop encephalitis or meningitis, which is an inflammation of the brain. Symptoms of this disease develop rapidly and may include high fever, headache, muscle weakness, stiff neck, confusion, and coma. The rate of fatality is 3-15% among those who develop the disease. WNV encephalitis primarily affects persons over 50 years of age. Those with a compromised immune system may also be more susceptible to acquiring encephalitis. Currently no approved human vaccine is available for WNV. The National Institute of Allergy and Infectious Diseases (NIAID) was awarded a development grant in 2000.

Courtesy of the National Pesticide Information Center Website

West Nile Virus in California

According to the California Department of Health Services, 52 of 58 counties in the state have had West Nile virus activity this year. Recent figures show there have been 8 deaths in California, with none being from Santa Clara county. West Nile has actually killed many more horses (120) and birds (1,734) when compared to its impact on human communities. In Santa Clara county specifically, there have been over 63 birds that have been found deceased due to West Nile virus infection.

District 10 Neighborhoods affected by West Nile

According to a recent article by John Woolfolk in the Aug. 27th edition of the San Jose Mercury News

Worried about an escalating outbreak of mosquitoes infected with deadly West Nile virus, Santa Clara County officials Friday said they plan for the first time to spray an insecticide fog in two San Jose neighborhoods as early as Thursday. Health officials insist the plant-based poison they will use, while deadly to mosquitoes, is not harmful to humans or pets, and that no special precautions are needed in the areas to be fogged. The two affected neighborhoods, each two square miles, surround Mia Circle at Branham Lane, and La Colina Park at Allegan Circle. The county is distributing an informational letter to about 6,800 residents living in the two spray areas, and will hold a community meeting Tuesday August 30th to answer questions. While this will be the first instance of fogging for West Nile in Silicon Valley, fog trucks and pesticide sprayed from airplanes have been in use for weeks in the Central Valley, notably in Sacramento County, where there have been 47 confirmed human cases of the disease this summer. By contrast, only one human case has been reported in Santa Clara County this year, and that victim, a 34-year-old woman who has since recovered, is thought to have contracted the disease in Sacramento. Many of the 62 dead birds and all of the mosquitoes that have been found carrying the deadly virus in Santa Clara County this year have been in the two areas scheduled for treatment.

``High concern''

``The area targeted to be fogged is of high concern,'' said Tim Mulligan, Vector Control District manager. ``Our job is to protect the health of residents, and by specifically targeting this area with ground fogging, we have the ability to suppress the West Nile-positive adult mosquito population, and have a significant impact on the number of human cases.'' Last month, vector control officials sprayed creeks and ponds in the same area with insecticide that kills immature mosquito larvae, which live in water.Next week's planned fogging operation will use a different chemical designed to kill adult flying mosquitoes, a step the district has only used previously in marshes, and not in recent years. ``Larval control is still the district's primary method of mosquito control,'' Mulligan said. Sudha Subramaniam, 38, who has lived on Mia Circle for four years and never had a serious mosquito problem, said she wasn't particularly concerned about West Nile virus but had no objection to the spraying. ``If the spray is going to kill the mosquitoes, then I guess they've got to do what they've got to do,'' Subramaniam said. ``I haven't experienced any mosquitoes inside my own house. But it's better to be safe than sorry.'' The chemical to be used, Pyrenone 25-5, will be misted into neighborhoods late at night using two trucks with mounted foggers, which dispense very fine aerosol droplets that stay aloft and kill adult mosquitoes on contact. The procedure is being used by other counties and cities and is consistent with state protocol. It has been shown to be safe for humans and domestic pets, district officials said.Pyrenone 25-5 contains pyrethrins, which are botanical insecticides produced from the extract of chrysanthemum flowers, said district officials. They are the most common ingredient found in popular household insect sprays, and also are found in head lice medicines for children and in pet shampoos.

Low in toxicity

When applied at mosquito control rates, pyrethrins are low in toxicity to people and animals, are non-carcinogenic, cause no adverse reproductive effects, and do not mar automobile finishes, district officials said. Pyrethrins break down in the environment, and high temperatures and sunlight accelerate this process. The amount of product being used in this instance is less than one ounce per acre. Weather permitting, the fogging is scheduled for Thursday between midnight and 4 a.m. -- a schedule aimed at avoiding traffic or breezes that could disrupt the operation. District education specialist Kriss Costa said the residential fogging is new for Santa Clara County, but is safe and widely used, so residents shouldn't worry. Costa said that in the past, the county has focused on killing mosquitoes in the larval stages. ``This fogging is going after adult mosquitoes,'' she said. ``This district has never done any fogging in residential areas. The beauty of this product we're using is that it's a very common ingredient in many household products. It's very benign.''

Six deaths in state

West Nile virus is spread to humans by the bite of an infected mosquito. The virus is not transmitted person-to-person. Some 300 Californians have contracted the disease so far this year, including the Santa Clara County woman who local officials believe was infected while visiting Sacramento. She does not live in the areas that will be sprayed, was never hospitalized, and has since fully recovered. But statewide, at least six Californians have died of the disease this year. West Nile virus produces flu-like symptoms in about two out of 10 people infected, and about one out of 150 infected people develop severe, life-threatening illness. The elderly are particularly vulnerable.

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