For many years, it was commonly thought that only certain parts of the world presented the risk of mosquito-borne illness. However, as our global community has grown and conditions around the world have changed, mosquitos are now a threat virtually everywhere. Most Americans don’t realize that the possibility of getting a serious disease from mosquitos is all too real, even within your own backyard.
Common Mosquito-borne Illnesses in America
Mosquitos are vectors for many illnesses. A single mosquito bite can transmit any number of diseases directly into the bloodstream. Common mosquito diseases in America are:
West Nile Virus (WNV): About 1 in 5 people with West Nile Virus develop a fever and other symptoms such as headache, body aches, joint paints, vomiting, diarrhea, rash, and fatigue and weakness. Fatigue may last for months. About 1 in 150 cases get severe symptoms such as encephalitis, meningitis, coma, vision loss, paralysis, and sometimes death. There are no vaccines or medicines to treat West Nile Virus. Cases most often occur in summer through fall and are most commonly spread through mosquito bites.
Dengue Fever: About 1 in 4 people with dengue will have symptoms, which usually include fever along with eye pain, headache, muscle pain, bone pain, joint pain, rash, nausea, or vomiting. About 5 percent of symptomatic cases have severe symptoms with internal bleeding, shock, blood in stool, vomiting blood, or bleeding from the nose or gums, and the disease may become life-threatening within hours. There is no specific medicine to treat dengue. Dengue is mostly spread through mosquito bites.
Zika Virus: Many people infected with Zika will have mild symptoms or no symptoms. Common symptoms of Zika are fever, rash, headache, joint pain, muscle pain, and conjunctivitis. There is no treatment medicine or vaccine for Zika virus. While mostly spread by mosquito bites, Zika can also be spread from person to person: from a pregnant woman to her fetus (may cause birth defects), and through sex.
Malaria: Malaria comes from a parasite and typically causes serious symptoms, including high fevers, shaking chills, and flu-like illness. Without treatment, severe complications and death can occur. About 2,000 cases are diagnosed in the U.S. annually; most of these are from travelers, which mosquitos may bite and subsequently spread the disease to others.
Mosquitos found in America can also cause other serious and potentially life-threatening diseases like:
- Cache Valley virus
- Chikungunya
- Eastern equine encephalitis
- Jamestown Canyon virus
- La Crosse encephalitis
- St. Louis encephalitis
This map of U.S. cases of mosquito-borne diseases shows where these diseases have been reported in the continental U.S. over the past decade.
Common Mosquito Species Found Across America
Most mosquitos in the U.S. are nuisance mosquitos. They do not spread germs that make humans sick, but they will still bite. However, species that do spread disease live among the rest, and their presence is often not detected until after they’ve already bitten. Here are the most common disease-carrying mosquitos in the United States:
- Anopheles mosquito (An. freeborni and An. quadrimaculatus): Known to spread malaria.
- Aedes mosquito (Ae. aegypti): Known to spread chikungunya, dengue, and Zika viruses.
- Culex mosquito (Cx. pipiens, Cx. tarsalis, Cx. quinquefasciatus): Known to spread West Nile virus.
Many mosquitos bite during the day or night, which is contrary to the popular notion that mosquitos only bite at dawn or dusk. They may also live indoors or outdoors.
Where Mosquitos Are Found Across America
Mosquitos that can transmit serious diseases are found across the United States. The three most common disease-carrying mosquitos (listed above) are found in the following regions:
| Anopheles mosquito | Aedes mosquito | Culex mosquito |
| Eastern U.S. Western U.S. | East Coast Midwest West Coast Southern U.S. | Throughout the U.S. |
The worst U.S. cities for mosquitos are Los Angeles, CA; Atlanta, GA; Washington, D.C.; Dallas, TX; Chicago, IL; New York, NY; Detroit, MI; Miami, FL; Charlotte, N.C.; and Raleigh-Durham, N.C.
Some mosquitos, such as Aedes mosquitos, prefer to live near people. Others prefer to live in marshes, forests, or tall grasses. All mosquitos prefer water, especially stagnant water (anything from major lakes to swimming pools to small containers that hold rainwater). Water is the ideal breeding ground for mosquitos and allows them to increase their population exponentially.
In short, mosquitos are everywhere in the United States. Controlling the mosquito population and finding safe and effective ways to prevent mosquito bites in the first place are both critical parts of reducing the spread and risk of mosquito-borne illnesses.