Vector (Mosquito-borne Disease) Control

Program Overview and Policies

The City of Cedar Hill partners with Dallas County Health and Human Service (DCHHS) to conduct the West Nile Virus surveillance and testing program. Each week, mosquito traps are set, collected and tested in mosquito management areas (MMA). Mosquitoes are tested for West Nile Virus (WNV). When a "pool" of mosquitoes tests positive for WNV, DCHHS schedules vector control spraying in the MMA where the positive sample was trapped. The spraying takes place at night from a truck mounted sprayer.

The WNV surveillance and testing program functions to control the outbreak of disease. The program does not function to directly control the mosquito population which naturally rise and fall throughout the year. The City only schedules vector control spraying services in an affected MMA in response to a WNV positive. The City does not spray individual residences upon request.

For individual residences, you may seek private professional licensed pest control services to fit your needs. The City does not promote nor make recommendations on specific private pest control service companies. The City does not provide a list of companies.

Generally, mosquitoes populations are best controlled by eliminating the breeding sources (standing water). Spraying only kills adult mosquitoes. If left alone, breeding sources will continue to produce new adult mosquitoes. The Culex mosquito which carries West Nile Virus takes 4-14 days to go from larvae to adult mosquito. Other species may form into adult mosquitoes as fast as 48 hours.

An effective method to Fight the Bite is the "4D" Defense. 

1. Use DEET repellents. 
2. DRESS in long sleeves and pants. 
3. DRAIN standing water. 
4. Protect yourself during DUSK and DAWN.

For additional questions, contact Duy Vu, Environmental Manager, at 972-291-5126, extension 2819 or via email.

Pesticides Used for Vector Control Spraying

What is permethrin?

Permethrin is an insecticide in the pyrethroid chemical family. Pyrethroids (also known as synthetic pyrethroids) are insecticides chemically similar to pyrethrins found in natural pyrethrum. Natural pyrethrins are extracted from the flowers of the chrysanthemum, which have been recognized for centuries for their insecticidal activity. Pyrethroids do not have the extent of adverse effects on non-targets unlike other insecticide groups.

Pyrethroids are widely used in public health applications because of their relative safety for humans, high insecticidal potency at low dosages and rapid knock-down effects. First developed in 1973, pyrethroids are more stable to light than natural pyrethrum. Permethrin was originally registered for use by the United States Environmental Protection Agency (U.S. EPA) in 1979, and was re-registered in 2006.

What is permethrin used for?

Permethrin is registered for use on/in numerous food/feed crops, livestock and livestock housing, modes of transportation, structures, buildings (including food handling establishments), Public Health Mosquito abatement programs, and numerous residential use sites including use in outdoor and indoor spaces, pets, and clothing (impregnated and ready to use formulations).

According to Agency data, the EPA cites that approximately 2 million pounds of permethrin are applied annually to agricultural, residential and public health uses sites. The majority of permethrin, over 70%, is used in non-agricultural settings; 55% is applied by professionals, 41% is applied by homeowners on residential areas, and 4% is applied on mosquito abatement areas.

Permethrin is a restricted use pesticide for crop and wide area applications (i.e., nurseries, sod farms) due to high toxicity to aquatic organisms, except for wide area mosquito adulticide use. It is a general use pesticide for residential and industrial applications. Permethrin also has non-FIFRA pharmaceutical uses as a pediculicide for the treatment of head lice and scabies. The Food and Drug Administration (FDA) approves use of the pesticide-containing pharmaceutical under the Federal Food, Drug, and Cosmetic Act (FFDCA).

How much product does DCCHS apply when spraying occurs?

When Dallas County Health and Human Services sprays for adult mosquitoes the applications rate of active ingredient is no greater than .007 pounds per acre (AI)/acre). Most agriculture applications are performed at a rate of 0.2 to 0.4 pounds per acre.

What are the effects on other insects from spraying?

Extensive studies have shown little effect on insects from Ultra Low Volume (ULV) fogging for adult mosquitoes. ULV applications use Ultra Low Volumes, i.e. less than 1.0 ounce per acre, in microscopic sized droplets of a low toxicity product. We can minimize the negative non-target effects through the combination of ULV technology, limiting applications to periods of high annoyance or disease threat, and selecting the period of the evening when many other non-target insects are not active. Please note that although permethrin does present toxicity to bees, many bees are not flying/pollinating at the time mosquito spraying is performed.

What are the effects of permethrin exposure in humans?

Pyrethroids do not accumulate in the body and their excretion is rather rapid, even after repeated administrations: typically, 90% of the administered dose is excreted in urine and feces within a week after treatment. In addition, Permethrin has been used for many years, with no human poisoning cases reported. No indication exists that permethrin has a significant adverse effect on humans when used as recommended. It has induced skin sensations and paraesthesia in exposed workers, but these effects disappear within 24 to 48 hours. Transient numbness, itching, tingling, and burning sensations have been reported in a small percentage of humans after dermal exposure to permethrin when it was used to treat head lice (World Health Organization, 1990).

With respect to mosquito applications, many people do not risk any exposure to permethrin if their windows are closed and they are within their homes during a mosquito spraying application. The ULV spray does not stay in the air for much longer than 2-3 hours. The product will adhere to vegetation and therefore, people are not breathing in permethrin from a mosquito control application the morning after an application.

What is the half-life of permethrin?

In soil the average half-life of permethrin in aerobic soils is 39.5 days, with a range from 11.6 to 113 days. Permethrin binds tightly to soil and is broken down primarily by microorganisms, but also by photolysis.

When exposed to water some of the product is degraded. Some degradation also occurs due to sunlight while in the water column but the majority binds tightly to the sediment. The average half-life range for permethrin in the water column is about 19 to 27 hours, however permethrin adsorbed to sediments can persist more than a year. Permethrin is not likely to contaminate groundwater due to its low water solubility and strong adsorption to soil.

How much permethrin can people be exposed to?

The U.S. EPA has determined a Reference Dose (RfD) of 0.25 mg/kg/day for both acute and chronic dietary exposures to permethrin. The RfD is an estimate of the quantity of chemical that a person could be exposed to every day for the rest of their life with no appreciable risk of adverse health effects. The reference dose is typically measured in milligrams (mg) of chemical per kilogram (kg) of body weight per day. No human data were found on chronic effects of permethrin.

The U.S. EPA has not determined a Maximum Contaminant Level (MCL) for permethrin in drinking water. However, a limit of 0.3 mg/L was set by the World Health Organization (WHO) as a guideline for permethrin in drinking water when it is applied to water for mosquito control.

The Agency for Toxic Substances and Disease Registry (ATSDR) determined Minimum Risk Levels (MRLs) for oral exposures to technical grade permethrin of 0.3 mg/kg/day for acute oral exposures (up to 14 days) and 0.2 mg/kg/day for intermediate durations (15-364 days).

Is permethrin linked to the honey bee die off?

Funding has allowed for collaborative comparative studies to be initiated, including many professionals and experts from across the country to further investigate the phenomenon of Colony Collapse Disorder (CCD). CCD was largely documented in 2006 and was initially linked to varroa mites. Research on the declining bee population is only just beginning; with pathogens, environmental chemicals, and nutritional stressor being some of the most recent causes being considered. One class of pesticides under close scrutiny by beekeepers and the press are neonicotinoids, which are known to be quite toxic to honey bees. We strongly encourage you to review the current literature available to stay informed.

About West Nile Virus (WNV)

WNV is a potentially serious illness. It is transmitted by a bite from an infected mosquito that is already carrying the virus.

Most people will not show any signs of infection, but many will have mild symptoms such as fever, headache and body aches. Rarely, symptoms may require medical care or hospitalization. The people who are most susceptible to the disease are the very young, the elderly and those with weakened immune systems.

For more information:

Mosquito Safari Website

Additional West Nile Virus (WNV) Information

What is Zika Virus?

Zika virus is spread to people through mosquito bites. The most common symptoms of Zika virus are fever, rash, joint pain, and conjunctivitis (red eyes).

How Does Zika Virus Spread?

Zika virus is spread to people primarily through the bite of an infected Aedes species mosquito. The mosquitoes typically lay eggs in and near standing water in things like buckets, bowls, animal dishes, flower pots, and vases. They are aggressive daytime biters, prefer to bite people, and live indoors and outdoors near people. Mosquitoes become infected when they feed on a person already infected with the virus.

Infected moquitoes can then spread the virus to other people through bites. A mother already infected with Zika virus near the time of delivery can pass on the virus to her newborn around the time of birth. It is possible that Zika virus could be passed from mother to fetus during pregnancy.

Zika is an Emerging Virus 

As of January 2016, there were no reports of infants getting Zika virus through breastfeeding. Because of the benefits of breastfeeding, mothers are encouraged to breastfeed even in areas where Zika virus is found. As of January 2016, there was one report of possible spread of Zika virus through blood transfusion and one report of possible spread through sexual contact.

What are the Symptoms of Zika Virus?

About 1 in 5 people infected with Zika virus become ill (i.e., develop Zika). The most common symptoms of Zika virus are fever, rash, joint pain, and conjunctivitis (red eyes).

Other common symptoms include muscle pain and headache. The illness is usually mild with symptoms lasting for several days to a week. Severe disease requiring hospitalization is uncommon. Deaths are rare. See your healthcare provider if you develop the symptoms and have visited an area where Zika virus is present. If you have recently traveled, tell your healthcare provider when and where.

How is Zika Virus Treated?

No vaccine or medications are available to prevent or treat Zika infections. Treat the symptoms:

• Get plenty of rest.
• Drink fluids to prevent dehydration.
• Take medicines, such as acetaminophen or paracetamol, to relieve fever and pain.
• Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs), like ibuprofen and naproxen, should be avoided until dengue can be ruled out to reduce the risk of hemorrhage. If you are taking medicine for another medical condition, talk to your healthcare provider before taking additional medication.

What Should I Do If I Have Zika Virus?

If you have Zika virus, avoid mosquito bites for the first week of your illness. During the first week of infection, Zika virus can be found in the blood and passed from an infected person to another mosquito through mosquito bites. An infected mosquito can then spread the virus to other people. The best way to avoid Zika virus is to avoid mosquito bites. What Can I Do? Defend by using the 4Ds.

1. DEET All Day Every Day: Whenever you're outside, use insect repellents that contain DEET or other EPA approved repellents and follow instructions.
2. DRESS: Wear long, loose and light-colored clothing outside.
3. DRAIN: Remove all standing water in and around your home.
4. DUSK & DAWN: Limit outdoor activities during dusk and dawn when mosquitoes are most active.