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Mosquitoes and West Nile Virus
 | | by Carol Nagy Jacklin
and Sally Snipes
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The mosquito population is exploding. Our plentiful winter rain had the unfortunate side effect of leaving lots of standing water — the breeding ground of mosquitoes. West Nile Virus, which is carried by mosquitoes, has been fatal to humans in New York and Florida. It has continually spread westward, and Colorado had many cases in 2003. Birds and horses have been affected in Southern California.
The problem
West Nile Virus (WNV) causes encephalitis, an inflammation of the brain. The virus primarily passes from birds to one type of mosquito, the culex mosquito. It is fatal to most birds. Crows, stellar jays, scrub jays and ravens are particularly susceptible. San Diego County Department of Agriculture and Environmental Health Vector Control has been testing dead birds for several years and has found cases of WNV scattered all throughout the county. WNV has only arrived in the county in the last three years. Two horses have died here after being bitten by infected mosquitoes, but no human cases have been reported.
An infected mosquito can bite a healthy person and the virus may pass through them with no ill effects. Youngsters, oldsters, and folks with compromised immune systems can be made ill or even die from the virus. There is now an effective horse vaccine but no human vaccine is available. Dogs and cats don’t seem to be troubled.
The symptoms of the disease are different in different people. Some small percent develop a fever while in others the disease acts like a cold or flu.
What the County proposes to do
The county has sent ballots to all registered voters asking about county vector control (CVC) use in each county area. We learned a few details we thought we should pass on to you. The county wants to control the larval stage of the mosquito. They will use a granular spray to do so. They will not use a drifting fog spray. The granular material is B.T. (Bacillus Thuringiensis), a group of over 35 kinds of bacteria commercially produced to control mosquito larvae. When the larvae ingest the BT, their digestive systems are destroyed. It is completely harmless to plants, humans and pets. It only targets mosquitoes. Several applications 3-4 days apart are the most effective to control the hatching process.
Ponds and ditches will be monitored and treated if needed. Aerial surveillance will be used to find green swimming pools, which will also be treated. Chickens have been placed in various locations to act as sentinels. Their blood is regularly tested for WNV, to alert the county officials to any areas with large infestations.
In 2004 the county treated many locations. The treatment doesn’t take long. Last year they treated 27 locations in one day and the presence of WNV is very small here compared to the rest of the state. They report that they notify citizens the day before treatment of any area.
What can we do?
Check your property. If you find a dead bird, wrap it in a plastic bag and put it in a freezer immediately. Then call 858-694-2888. To test for West Nile Virus, the bird must be dead less than 24 hours for the laboratories to make a positive identification.
Mosquitoes cannot breed in moving water. But is there still water on your land? Mosquitoes can breed in very small amounts of water. They can even breed in plants, such as agaves and bromeliads that hold water between their leaves. Be sure to flush out the water at least weekly. If you have a pond get some gambusia, mosquito larvae eating fish. They are very effective and are given away free at 14 pet stores throughout the county. A list of the stores is available at the county’s web site: sdfightthebite.com or call (888) 551-INFO (4636).
If your pond is too small for fish you can buy Mosquito Dunk. Mosquito Dunk is a solid form of B.T. the granular bacteria that we talked about above. It is a slow releasing form, and will last up to a month or more in your birdbath or small pool. But it is a little pricey if you need a lot. Mosquito Dunk is for sale at garden stores, pet stores, and on line. Again, B.T. is not harmful to fish, birds, plants, or other animals. It is specific only to mosquitoes, which makes it particularly effective in the battle against West Nile Virus.
The very best thing we can do is be sure the breeding ground of the mosquitoes are eliminated. The County web site suggests we: Clean out pet bowls daily. Fix leaky faucets that cause water puddles, repair or install tight-fitting screens, cover or drain items that hold water, such as unused pools, trash cans, old garden equipment, and boats. Clean the water in birdbaths and wading pools at least weekly. Clean out clogged rain gutters. Clean out saucers under plants. Oak tree hallows can even be a breeding basin. Check out holes that may be full of winter rain or water from a sprinkler and drain them with a siphon or a sponge. Children’s dump trucks and old tires or plastic buckets need to be checked. Be sure to recheck after every summer thunderstorm.
You can only get West Nile Virus if an infected mosquito bites you. Dawn and dusk are the favorite times of day for mosquito action. You may just want to avoid being outside at these times. Instead, take those times to look out and admire your garden that’s cleansed of mosquito breeding places and everyone in the county will have a nicer summer!
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