Mosquito-Borne Illnesses

Until the mid-1980s, waste tires were considered more of a nuisance and environmental threat than the possible foci of mosquito-borne disease epidemics. This changed in 1985 when a substantial breeding population of Aedes albopictus was discovered in Houston, Texas. It is probable that this population arrived from Japan as eggs deposited inside used tires. The design of tires makes them ideal breeding sites for several species of mosquitoes, some of which are very important vectors of disease. Since they are easily filled by rain and collect leaf litter, they provide an ideal "incubator" for mosquito larvae. Of the mosquito problems associated with waste tires, it probably is safe to say that 20% of the tires are responsible for 80% of the problem. If we can eliminate scrap tire dumps and ensure processors comply with used tire management standards (statutes/regulations), we will eliminate a prolific mosquito habitat and the associated disease risks.

House Mosquito ( Culex Pipiens), Tree-hole ( Aedes triseriatus) ¹, Asian Tiger ( Aedes albopictus) The Culex pipiens mosquito, which bites from dusk to dawn, is a vector of St. Louis encephalitis and West Nile virus. It becomes infected by feeding on birds that carry these viruses. Although these viruses affect mostly older adults and the immune deficient, the risk is present to the entire human population. The tree-hole mosquito, which bites during the day, is the main vector of California (La Crosse) encephalitis in Illinois. The virus infects chipmunks, squirrels and other small woodland animals; in humans, it affects mainly children. Aedes albopictus was brought into the United States and other countries through the worldwide transport of used tires. The Asian tiger mosquito transmits dengue fever in other parts of the world, the West Nile Virus, and could become involved in the California encephalitis cycle in Illinois (IDPH).

¹The scientific name for Aedes triseriatus was recently changed to Ochlerotatus triseriatus.

Encephalitis is an inflammation of the brain that can be caused by viruses, including viruses carried by mosquitoes. Only appropriate serological testing can determine if a mosquito-borne virus is the cause of a case of encephalitis. The symptoms of encephalitis can range from mild to severe. Severe symptoms include rapid onset of severe headaches, vomiting, high fever, and mental disturbances such as confusion, irritability, tremors, stupor and coma. Severe cases sometimes end in death or with survivors suffering permanent loss of limb function, reduction of intelligence and/or emotional instability.

For more information on Encephalitis:

• Center for Disease Control's Information on Arboviral Encephalitides
• Illinois Department of Public Health - Mosquitoes and Encephalitis

St. Louis Encephalitis (SLE) is primarily spread by the Culex mosquito and is the most common mosquito-transmitted human pathogen in the U.S. Overall, there have been 4,437 confirmed cases of SLE with an average of 193 cases per year. The fatality rate is 5-15%.

La Crosse Encephalitis (LAC) is primarily spread by the Ochlerotatus triseriatus with most cases occurring in children under the age of 16. An average of 75 cases occur per year with 1% death rate. In Illinois, there are 5-15 cases of LAC (La Crosse Encephalitis) per year (Linn Haramis, IDPH).

West Nile Virus (WNV) is primarily spread by the Culex mosquito and the Asian Tiger mosquito. As of July 10, 2002 there have been 150 total human cases including 18 fatalities in the U.S. Symptoms generally occur 3 to 15 days following the bite of an infected mosquito and range from a slight fever, headache, rash, swollen nodes and conjunctivitis (irritation of the eye), to the rapid onset of a severe headache, high fever, stiff neck, disorientation, muscle weakness, coma or death. The case fatality rate ranges from 3 percent to 15 percent. American Crows and Blue Jays are particularly susceptible to the WNV.

The National Pesticide Information Center (NPIC), a cooperative effort of the United States Environmental Protection Agency (EPA) and Oregon State University has developed a West Nile Virus Resource Guide.

New cases are being found in Illinois at a shocking rate (IDPH). In 2002, birds, mosquitoes and horses in 100 of Illinois' 102 counties tested positive for West Nile virus; the first Illinois human cases and deaths from West Nile disease were reported in August. By November, the state had recorded more than 700 cases and 48 deaths, both totals the highest in the nation. Human cases were reported in nearly half of the state's counties, but the overwhelming majority were in Cook County. Cases ranged in age from 3 months to 97 years; the average age was 56.

Aedes albopictus is a very aggressive daytime biter with peaks generally occurring during the early morning and late afternoon. Adult males and females are covered with shiny black scales with distinct silver white bands on the palpus and tarsi. Its most striking characteristic is the band of silver scales forming a distinct stripe on the dorsal surface of the thorax and head. The flight range of adults is limited, and they have not been observed to fly in strong winds. Its major means of dispersal is through the transport of used and waste tires. Depending on temperature and the availability of food, Aedes albopictus can complete larval development between 5 and 10 days. The eggs of Aedes albopictus are similar to Aedes aegypti. Discarded automobile and truck tires are an important habitat of Aedes albopictus.

Ochlerotatus triseriatus

Ochlerotatus ("tris") has become an important urban mosquito because of its association with scrap tires. Even though the accepted common name for "Tris" is the Eastern Treehole mosquito, it also uses tires as a major breeding ground. It can be found in a single water-filled tire behind the garage or in a tire dump with thousands of tires. In scrap tire yards, adults reach incredibly high numbers, as many as 60,000 females per acre in mid-summer. The major food source for the Ochlerotatus triseriatus larvae is decomposing leaves collected in used tires. The most diagnostic characteristic of "Tris" is the silvery scales covering the sides of the thorax. The abdominal segments are dark and un-banded. The flight range of adults is rather short and often ranges only a few hundred yards from the treehole or tire pile where they are produced. Ochlerotatus triseriatus females can pass the Lacrosse virus on through the eggs to the next generation thus providing an overwintering mechanism for the virus.

Culex pipiens                                       
Culex pipiens, or the northern house mosquito, is the most common species of mosquito found in urban areas. Adults of the Culex pipiens are light brown mosquitoes identified by the presence of distinctive, basal, pale abdominal bands. Abdominal bands are broadly rounded medially and distinctly constricted sub-laterally before joining large, lateral scale patches. Members of the Culex pipiens complex are the principal vectors of St. Louis encephalitis (SLE) virus in the central and eastern United States. Eggs hatch in 1-2 days. Development from egg to adult is temperature dependent, requiring 8 to 12 days in summer. Females may travel considerable distances from resting sites to search for blood hosts, and marked females have been shown to travel up to 1100 m in a single night. However, maximum flight range is about 1-2 miles.                                  

Mosquitoes use visual, thermal, and olfactory stimuli to locate a host. Avoid mosquito bites to avoid infection.

1. Wear appropriate clothing.
   1. Light colored (dark colors attract mosquitoes)
   2. Long pants and top
   3. Tightly woven material
2. Wear a bug spray with DEET (N, N-diethyl-3-toluamide) as the major ingredient. Concentrations of 5% to 100% are available.
   1. Products with 25-35% DEET will provide adequate protection for general circumstances. (A 24% concentration will provide protection for about 5 hours) (Study from the New England Journal of Medicine)
   2. Avoid spraying plastics, rayon, or synthetic fabrics
3. For extra protection in severe circumstances a combination of Permethrin and 35% DEET can be used to provide 99.9% protection.
   1. Permethrin (a human-made synthetic) should be applied directly to clothing. To apply to clothing, spray each side of the fabric (outdoors) for 30 to 45 seconds, just enough to moisten it. Allow the garment to dry for 2 to 4 hours before wearing it. ( Annals of Internal Medicine Study)
4. Don't wear cologne or perfume

Excellent articles on insect repellents

By controlling the mosquitoes at the tire facilities, we can greatly reduce the risk of encephalitis to workers and nearby residents. For example, in Ohio over 60% of La Crosse encephalitis cases are associated with used tires.

The larvicides available to control mosquito larvae include Abate ^R, VectoBac ^R, VectoLex ^R, and Altosid. The Abate pellets have been effective since 1965 and are the most cost effective larvicide on the market today. VectoBac ^R is a biological larvicide that has no adverse effects on humans, and has had no cases of resistance in the field. VectoLex ^R is particularly effective against the Culex mosquito larvae, which is known to carry the WNV and St. Louis encephalitis. Altosid ^R provides long-term protection by using an insect growth regulator called methoprene, which interferes with the metamorphoses of mosquitoes. This product is available in several different forms including granules, bricquets, liquid and pellets.

There are several different adulticides available for adult mosquito control, including Biomist ^R, Anvil ^R, and Scourge ^R. Biomist ^R, which contains permethrin, has a fast knockdown time, low mammal toxicity, and is 80% biodegradable on plant surfaces within 24 hours. Anvil ^R uses Sumithrin and is best used around creeks, swamps, and residential areas with high numbers of mosquitoes. This product has a high knockdown rate and is effective against organophosphate-resistant species. Scourge ^R combines Resmethrin and Piperonyl Butoxide and is available in two different concentrations 18%+54% or the 4%+12% ready-to-use formula.

Initial screening tests in a New Orleans laboratory have shown that the Asian Tiger Mosquito may be as much as 5 to 6 times as difficult to kill as some of the native mosquitoes. Because of this, different combinations may be needed to control different mosquito populations. In this study the control measures included using a combination of adulticides applied by Ultra-Low Volume spray. Malathion and Resmethrin (Scourge) were used to control adults. Chlorpyrifos (Dursban) and Bacillus thuringiensis Berliner var. israelensis were used to control larvae in tires (Ohio State University Extension).

The most effective mosquito control is to keep tires dry. Chemical treatment of tire piles to control either larval or adult stages is much more difficult than most routine applications and may not be fully effective. Shredding tires, or otherwise rendering them incapable of holding water and supporting mosquito production substantially decreases mosquito populations and is usually more preferable than attempting control through the application of larvicides and adulticides. However, studies show that a small percentage of mosquito larvae survive shredding, allowing the dispersal of larvae at a lower rate. Because of this, a combination of shredding, draining, and the use of larvicides/ adulticides may be needed to control the mosquito infestation in some areas.

Although tires are the major haven for mosquitoes, they can be found in almost any place capable of holding water. Soda cans, birdbaths, rain gutters, toys, pool covers, tree stumps, and garbage cans are all capable of harboring mosquitoes. Therefore, it is important to drain anything capable of retaining water at least once a week to prevent the larvae from hatching.

According to the Illinois Department of Public, if a dead crow or blue jay is found between May 1 and the end of October and appears to have died of natural causes, you should report the "sighting" to your local health department. If it appears that birds, especially crows, are dying at an unusual rate, some dead birds will be collected for testing for WNV and other possible causes of bird deaths.

If you have any specific questions about the mosquito populations or the diseases spread by these mosquitoes please contact:

Linn Haramis, Ph.D.,                                    
Entomologist / Vector Control Program Manager                                    
Illinois Department of Public Health                                    
Division of Environmental Health;                                    
525 W. Jefferson St. Springfield, IL 62761;                                    
217-782-5830 Fax: 217-785-0253

Illinois Department of Public Health West Nile Virus hotline: 866/369-9710

For questions concerning the removal of used tires in your area please contact the Illinois Environmental Protection Agency's Used Tire Program at 217-785-8604.

Centers for Disease Control

US Geological Survey        

Clarke Mosquito

University of Florida - Medical Entomology Laboratory