Lots of rain leaves standing water. Standing water attracts mosquitoes. Mosquitoes can carry West Nile Virus. And July is the prime month for cases of the disease to start showing up, said a Texas Cooperative Extension specialist.
Dr. Greta Schuster, an extension integrated pest management specialist in Canyon, will be dragging out her carbon dioxide light traps this week to determine how many positive mosquitoes can be found in the area. Schuster, who also is a West Texas A&M University associate professor, is working with Dr. James Alexander and the Texas Department of State Health Services.
Alexander reported West Nile Virus is already active in Texas, with one human case in Willacy County.
Positive mosquitoes have been found in Collin, Denton, Jefferson, Montgomery and Willacy counties.
West Nile Virus cases in Texas can be found at www.dshs.state.tx.us/idcu/disease/arboviral/westNile/ .
In 2006, 33 West Nile human fatalities were reported and since 2002, 71 fatalities due to the virus have been reported in Texas, Schuster said, quoting state health service figures.
Schuster has been sampling for West Nile virus-carrying mosquitoes for the past five years. She started in an effort to help extension agents and area veterinarians know the severity of the situation and to help get horses vaccinated for the disease.
Each year she watches the reports from other parts of the state to know when to start collecting mosquitoes. When the positive cases start showing up in the south, she knows it won't be long before the virus moves north.
When Schuster collects the live mosquitoes in her traps, she sends them to the Texas health department in Austin where they are tested to see if they carry the disease.
"We're trying to find out when mosquitoes are becoming active and what species is active at the time," she said.
With all the recent rain in Texas, a large hatch of mosquitoes can be expected, Schuster said.
"If they are showing up in my traps, then there are a lot more out there," she said. "That's when we start alerting the Texas Department of Agriculture and other agencies who can get the word out that it is time to be more vigilant in control and protection."
To protect against disease-carrying mosquitoes, Schuster said wear long sleeves when working outdoors, use a DEET product and don't go out from sundown to 10 p.m., if possible.
"When we were collecting mosquitoes off the horses, they were covered the heaviest from about 8-10 (p.m.)," she said.
Schuster said there is some concern about using products with the DEET chemical in it, but advises that if people spray most of the chemical over their clothing and use long sleeves to protect themselves, it is safe.
The DEET amounts in products vary, she said. The amount needed depends on how long an individual expects to be outside. The more DEET the repellent contains, the longer, not better, it will protect.
The Centers for Disease Control and Prevention advise that products with a low concentration of active ingredient may be appropriate when exposure to insects is minimal, Schuster said.
Higher concentrations of active ingredient may be useful in highly infested areas or with insect species which are more difficult to repel.
When trying to limit mosquito populations outside, a combination of treatments is best, Schuster said.
"First, we advise sanitation," she said. "Empty water from flower pots, pet food and water dishes, birdbaths, swimming pool covers, buckets, barrels and cans. Remove discarded containers and other items that could collect water."
Second, use a larvicide chemical to control hatching mosquitoes so they never become adults, Schuster said. Larvicides, which kill immature mosquitoes, are put in water sources.
Bacillus thuringiensis, more commonly know as BT is a biological larvicide that is safe for animals, she said. It is found in products sold as Mosquito Dunk.
Methoprene, a chemical larvicide, is an insect growth regulator that kills larvae by disrupting their development.
As with all products, Schuster advised, read and follow all labels and directions.
The final step to treatment is the use of adulticides or products used to kill adult mosquitoes, she said.
These products can immediately reduce the number of adult mosquitoes around the home.
They include fogs, mists or sprays, which are often used by city and county officials to treat large areas, she said.
"There's no one control that works the best," Schuster said. "It's a combination of all of them.”