Each summer, hordes of these insects descend on backyards, parks and campgrounds. While most mosquitoes are merely nuisances, some can transmit serious diseases such as encephalitis and malaria in humans and heartworm disease in dogs.
What kinds of mosquitoes are common in Illinois?
Two different kinds of mosquitoes plague Illinoisans. Floodwater (temporary pool) mosquitoes deposit their eggs singly in low-lying areas that will be flooded later. Under normal summer temperatures, large numbers of biting mosquitoes will emerge about two weeks after heavy rains and can be a major nuisance problem for several weeks. The most common of these in Illinois is the inland floodwater mosquito. A vicious biter, this mosquito will commonly fly 10 or more miles from where they hatch, particularly along prevailing winds. Floodwater mosquitoes have not been significant disease carriers in Illinois.
Vector mosquitoes carry diseases and lay their eggs in stagnant ditches and sewage treatment ponds or water in treeholes, old tires, clogged gutters, old tin cans and anything else that will hold water. Eggs are laid on or just above the water surface, where they usually hatch within two to three days. Two of the more common vector mosquitoes in Illinois are the Culex, or house mosquito, and the tree-hole mosquito. Neither migrates long distances.
Another disease-carrying mosquito is the Asian tiger mosquito, which arrived in the United States in 1985 in old tires. An aggressive day-biting mosquito, it breeds in large numbers in water-filled artificial containers.
Do all mosquitoes carry disease?
Floodwater mosquitoes are not major vectors of human disease in Illinois, but they do transmit heartworm disease in dogs, as do Culex mosquitoes. The worms live and reproduce in the heart and pulmonary vessels and can severely weaken or kill the dog. Although difficult to treat, the disease is easily prevented by medication prescribed by a veterinarian.
In Illinois, the most common human illness carried by mosquitoes is encephalitis. This inflammation of the brain is caused by viruses and the disease can range from mild to severe. Severe symptoms include rapid onset of severe headaches, high fever and mental disturbances, such as confusion, irritability, tremors, stupor and coma. Severe cases sometimes end in death or with survivors suffering permanent physical and mental disabilities.
Mosquitoes do not carry all types of encephalitis virus, but they do carry at least three that can cause illness. The Culex 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. St. Louis encephalitis and West Nile virus affect mainly older adults. The tree-hole mosquito, which bites during the day, is the main vector of California (LaCrosse) encephalitis in Illinois. The virus infects chipmunks, squirrels and other small woodland animals; in humans, it affects mainly children. The Asian tiger mosquito transmits dengue fever in other parts of the world and could become involved in the California encephalitis cycle in Illinois.
The last major nationwide epidemic of mosquito-borne encephalitis occurred in 1975. In Illinois, 578 cases of St. Louis encephalitis, which resulted in 47 deaths, and 23 cases of California encephalitis were identified during that year.
When was West Nile virus found in Illinois?
West Nile virus was first identified in September 2001 when laboratory tests confirmed its presence in two dead crows found in the Chicago area. The following year, the state's first human cases and deaths from West Nile disease were recorded and all but two of the state's 102 counties eventually reported a West Nile positive, human, bird, mosquito or horse. By the end of 2002, Illinois had counted more human cases (884) and deaths (66) than any other state in the nation. In 2003, the number of human cases fell to 54 and only one death, and West Nile activity was reported in 77 counties.
What is the best way to reduce populations of mosquitoes?
The first and best defense against these pests and the illnesses they may carry is to eliminate the places where they breed. Here are a few suggestions:
How can people protect themselves from mosquito bites?
of Public Health
535 West Jefferson Street
Springfield, Illinois 62761
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