Mosquitoes are more than just a nuisance in summertime. They can be vectors (transmitters) of several diseases that can cause severe illness and even death in humans, including malaria, dengue fever and West Nile fever. In fact, they have been called one of the world’s deadliest animals because they kill more people than do sharks.
The most effective way to avoid mosquito-borne diseases is to protect yourself from mosquito bites and eliminate sources of standing water on your property where mosquitoes like to breed.
People hiking, camping, hunting and fishing need to take special precautions, especially when around mosquito breeding areas. Be prepared with insect repellent, protective clothing, mosquito netting and the shelter of your car or tent.
Below are some information on mosquitoes, the diseases they carry, actions you can take to protect yourself and your family, and other helpful resources.
Mosquitoes are small, long-legged, two-winged insects belonging to the order Diptera. Worldwide, there are over 2,600 known species. In Indiana, 53 species have been identified, of which 40 are known to exist in Allen County.
Mosquitoes have four distinct stages of development: 1) egg, 2) larvae, 3)pupae, and 4) adult. Eggs must be in water in order to hatch. Larvae and pupae are aquatic while adults are active, free-flying insects.
- Illustration of Mosquito Life Cycle (Purdue University)
Male mosquitoes emerge from the pupal stage about twenty-four hours before the females. Mating occurs within forty-eight hours, so the majority of females in any population are always fertile. Both females and males utilize nectar and other plant juices as energy sources; only females take a blood meal, utilizing the protein to produce eggs.
Mosquitoes can be placed into two categories. One category consists of mosquito species that lay their eggs on the surface of water, while the other category is mosquitoes that lay their eggs on a moist surface next to or above water.
Surface egg-laying mosquitoes deposit their eggs singly or in rafts that may hold 100 to 200 eggs on top of shallow standing water and hatch within 2-3 days. Indiana mosquitoes that have direct-hatching eggs include those that are vectors of West Nile virus, namely species in the genus Culex. Culex lay eggs on water in clogged gutters, tires, birdbaths, dried-up ditches, and un-maintained swimming pools. Anopheles species lay several single eggs on open bodies of water.
Mosquitoes in the second category can be labeled “floodwater” mosquitoes. They will hatch when the water covers the eggs and the conditions are correct. An example is eggs are laid on wet leaves next to a low area in the middle of the woods. A heavy rain fills up the low area and the eggs are covered. If the temperature is warm enough, the eggs hatch. If there is no rain, the eggs are protected by a hard cover and may survive up to ten years. The majority of nuisance mosquitoes are floodwater species, such as Aedes vexans and Psorophora ciliata. Aedes triseriatus, a vector of LaCrosse Encephalitis, lays her eggs along the insides of treeholes and artificial containers.
Mosquitoes also differ in the time of day when biting occurs. Some species bite during the day, while others only bite at night. Aedes triseriatus is a day-time biter, while Culex pipiens is a dusk to dawn biter.
Diseases Carried by Mosquitoes
Mosquitoes are responsible for the spread of many diseases throughout the world. Yellow fever, malaria, dengue fever and chikungunya are common in tropical regions. For those living in the Midwest, encephalitis is the disease of most concern.
Encephalitis is an inflammation of the brain, which can be caused by a mosquito-borne virus. The onset of the disease is usually sudden and the symptoms may include high fever, headache, nausea, vomiting, stiff neck, dizziness, drowsiness progressing into a coma, muscular twitching, and convulsions. In serious cases, death can occur.
In Indiana, there are four kinds of mosquito-borne encephalitis of major concern: Eastern Equine Encephalitis (EEE), LaCrosse Encephalitis (LAC), St. Louis Encephalitis (SLE), and West Nile virus (WNv).
For descriptions of these diseases, click on the tabs below.
Vector: Aedes or Culex species. Mosquitoes become infected by feeding on birds infected with the EEE virus.
Incubation period: 3 to 10 days
Illness: Many persons infected with EEE virus have no apparent illness. In those persons who do develop illness, symptoms range from mild flu-like illness to EEE (inflammation of the brain), coma and death. Mortality rate is about one-third, making it one of the deadliest mosquito-borne disease in the United States. There is no specific treatment for EEE; optimal medical care includes hospitalization and supportive care. About half of the people who survive will have mild to severe permanent neurological damage.
Case rate: About 5 cases reported annually in the United States
Most at risk: Persons in endemic areas and people over 50 and under age 15.
Learn more about Eastern Equine Encephalitis
Vector: Aedes triseriatus (tree hole mosquito). Mosquitoes become infected by feeding on invertebrate hosts such as chipmunks and squirrels infected with the LAC virus.
Incubation period: 5 to 15 days
Illness: Clinical features are frank encephalitis progressing to seizures, coma; majority of infections are sub-clinical or result in mild illness. There is no specific treatment for LAC.
Case rate: About 70 cases reported annually in the U.S.
Most at risk: Children (who are less than 16 years old; live, play or work near a woodland habitat; or, have tree holes or artificial containers around their
home) are most at risk for LAC.
Learn more about LaCrosse Encephalitis
Vector: Culex species. Mosquitoes become infected by feeding on birds infected with the SLE virus.
Incubation period: 5 to 15 days
Illness: Mild infections occur without apparent symptoms other than fever with headache. More severe infection is marked by headache, high fever, neck stiffness, stupor, disorientation, coma, tremors, occasional convulsions (especially in
infants) and spastic (but rarely flaccid) paralysis.
Case rate: 130 cases reported annually in U.S.
Most at risk: Elderly and persons who work outdoors
Learn more about St. Louis Encephalitis
Vector: Mainly Culex species, but a few Aedes species also. Mosquitoes become infected when they feed on infected birds. WNv can also be spread by blood transfusions, transplants, and from mother-to-child through breast milk.
Incubation period: 3 to 14 days
Illness: Most people (about 4 out of 5) who are infected will not have any symptoms or very mild symptoms such as fever, headache, body aches, swollen lymph glands or a skin rash. A small number of people infected with WNv will develop severe illness. The severe symptoms can include high fever, headache, neck stiffness,
stupor, disorientation, coma, tremors, convulsions, muscle weakness, vision loss,
numbness and paralysis. Symptoms may last several weeks, and neurological effects may be permanent. There is no specific treatment for WNv, except supportive care for severe cases.
Case rate: Varies
Most at risk: People age 50 or older.
Learn more about West Nile virus
All mosquitoes require standing water (at a minimum of 1/4 inches deep) for the first three stages of development. Consequently, the key to reducing mosquito breeding is to get rid of any vessels capable of holding water for extended periods of time.
To reduce the risks of mosquito-borne disease, do the following:
- Check your property for breeding sites. Flush out birdbaths once a week. Clean out clogged gutters. Empty or turn over wading pools when not in use. Dispose of containers, trays, and can that can hold water. Fill in tree holes with sand, gravel, cement or paintable foam. Get rid of old tires. For a list of tire recycling centers in Allen County, click here.
- Maintain backyard swimming pools and spas to discourage the development of mosquitoes. If the pool is not in use, place a cover over the pool and pitch it in the middle so the cover will not collect leaves and rain water.
Aerate ornamental ponds and water gardens. You can also get mosquito-eating fish to place in these ponds.
Limit time spent outdoors during peak mosquito biting times. Peak times tend to be at dawn and dusk, but some mosquitoes bite during the day.
Wear loose, light-colored, long sleeves and pants. Covering up exposed skin will help reduce the chances of getting bitten.
Use a repellant that contains DEET, picaridin, oil of lemon eucalyptus or IR3535. Repellants can be used on children, 2 months and older, but check the label before applying. Apply the repellent to clothing and exposed skin according to the label instructions.
- Purchase a hand-fogger or use a barrier spray when working outside or having a backyard party. You can also mix 2 tablespoons of malathion with a gallon of water. Spray this under bushes and high weeds. The mixture will kill adult mosquitoes resting on leaves and branches.
- Report dead birds or standing water to the Department of Health’s Vector Control & Environmental Services division by calling (260) 449-7459. Dead birds may be a sign that mosquito-borne disease is circulating between birds and the mosquitoes in an area. By reporting dead birds, you can help us with our monitoring and surveillance efforts. The department will also treat bodies of standing water with larvicide to kill mosquitoes before they hatch.
The Department of Health’s mosquito control program focuses on eliminating potential breeding sites, larviciding to reduce the mosquito population, and placing traps to collect and test mosquitoes for disease.
Below is more information on our mosquito control efforts.
The Department of Health’s Vector Control division inspects and treats mosquito known breeding sites identified throughout Allen County each summer. The products used to control the mosquitoes in the water are EPA-approved and environmentally-friendly.
Biological control requires introducing a natural predator into the habitat of the mosquito. Dragonflies, praying mantids, bats, and purple martins have been promoted as natural controls, but have not shown the ability to significantly reduce mosquito populations.
Gambusia affinis, also known as “mosquitofish”, is a top-feeding guppie that offers excellant control of larvae and pupae in ornamental ponds and backyard garden pools. These fish have upturned mouths and work along the surface, feeding on mosquito larvae and other small invertebrates. They are somewhat tolerant of organic pollution and reproduce rapidly.
Since the fish will interfere with the life cycle of other aquatic organisms around them, certain restrictions apply as to where they can be used. In general, they cannot be placed in an area, such as rivers, creeks, ditches, and lakes, where they will interfere with any Indiana game fish.
If you are interested in acquiring “mosquitofish” for your backyard pond, contact the Vector Control and Environmental Services Division.
As part of its mosquito control program, we also trap and test adult mosquitoes for disease. When trapped adult mosquitoes are identified carrying a mosquito-borne virus such as Eastern Equine Encephalitis or St Louis Encephalitis, the department may respond by spraying a half-mile radius area around the traps with an EPA-approved adulticide to reduce the numbers of mosquitoes that could be carrying the virus. The spraying occurs at night, when the temperature is above 55° F, and the wind speed is between 1 to 10 miles per hour.
- 2018 Allen County Mosquito Test Results (DOH)
- AquaAnvil Label & SDS
- Adulticide Information (EPA)
- National Pesticide Information Center
The Culex species, capable of transmitting West Nile virus, like to breed in tires, containers, and un-maintained swimming pools. Aedes triseriatus, carrier of LaCrosse Encephalitis, prefers to breed in treeholes or containers. Tenants and homeowners are provided with a warning to remove containers and tires or maintain their pools to prevent mosquito breeding. If the violations are not resolved, then legal action will occur per county ordinance.
Below are links to videos and publications regarding mosquito-borne disease prevention.
Mosquito Safety (DOH)
- Going to the Caribbean? Poster [En español] (CDC)
- Were You Recently in the Caribbean? Poster [En español] (CDC)
- Chikungunya Virus in the Americas (CDC)
- Chikungunya Virus Fact Sheet for Health Care Professionals (CDC)
- Chikungunya Virus (CDC)
- Chikungunya Virus Information (CDC)
- Chikungunya Virus Quick Facts (ISDH)
- FAQs about Chikungunya Virus (DOH)
- Zika Virus (ISDH)
- Zika Virus (CDC)
- Zika Virus – Pregnant Women (CDC)
- Zika Virus – Healthcare Providers (CDC)
- Zika Virus – Traveler’s Health (CDC)
- Zika Virus (WHO)
- Eastern Equine (Purdue University)
- LaCrosse (Purdue University)
- St. Louis Encephalitis (Purdue University)
- WNv (Purdue University)
- WNv Guidance for Clinicians (CDC)
Prevention & Control Information
- Keeping Students Safe from Animals & Insects (DOH)
- Bug Off Brochure (DOH)
- Insect Repellents (EPA)
- Interactive Identification of Mosquito Breeding Sites in the Community (Purdue University)
- How Do I Choose an Insect Repellent? (CDC)
- Insect Repellent Locator (NPIC)
- Tire Recycling List (DOH)
- Mosquito Fish (DOH)
- Choosing a Repellent for your Child
- National Pesticide Information Center (En español)
- Eliminar hábitats de mosquitos (EPA)
- Repelentes contra mosquitos (EPA)
- 2017 Allen County Mosquito Surveillance & Control Report (DOH)
- 2016 Allen County Mosquito Surveillance & Control Report (DOH)
- National WNv Human Case Activity (CDC)
- National Mosquito-Borne Disease Map (USGS/CDC)
- National Arboviral Numbers 1999 – 2017 (DOH)
- Indiana WNv Activity (ISDH)
- West Nile Virus Tally 2002 – 2017 (DOH)