In the United States, there are hundreds of species of mosquitoes. Most mosquitoes do not feed on humans or spread disease, but some mosquitoes carry viruses that can cause disease in humans and animals. Reducing exposure to mosquitoes is the most effective prevention method for mosquito-borne diseases.
General Mosquito-Borne Disease Information
Geographic Distribution and Seasonality
Mosquitoes and mosquito-borne diseases are found across the country. Cases of mosquito-borne disease are most common during warmer months (April to September), when mosquitoes are most active.
Hosts and Transmission
Mosquitoes feed on a variety of animals including: rodents and other mammals, birds, reptiles, and amphibians. Disease is spread by the bite of an infected mosquito. Some species of wildlife are affected by mosquito-borne disease as well.
Signs and Symptoms
For most mosquito-borne diseases, most humans do not develop symptoms or only have very mild symptoms. Human symptoms of mosquito-borne illness usually appear within a few days to 2 weeks after the mosquito bite and include:
- Fever and chills
- Headache and muscle aches
- Nausea and vomiting
Prevention and Control
Reducing exposure to mosquitoes is the best prevention method for mosquito-borne diseases, especially in warmer months and during peak mosquito hours (dusk to dawn), when mosquitoes are most active. To help prevent getting mosquito-borne illness while visiting the parks:
- Wear insect repellants that contain: DEET, IR3535, Picaridin, or oil of lemon eucalyptus (Para-menthane-diol); follow label instructions and reapply as needed;
- Wear long sleeves, long pants, and socks outdoors when weather permits;
- Treat clothing and gear with products containing permethrin
- Help reduce the number of mosquitoes around your home or campsite by emptying standing water from buckets, pet water dishes, and other items on a regular basis.
Testing and Treatment
There is no specific treatment for many mosquito-borne viral diseases, but supportive care can improve clinical outcomes.
If you think you have the symptoms of a mosquito-borne disease and your fever does not resolve or symptoms get worse, seek medical care.
One Health and Mosquito-Borne Disease
West Nile Virus, chikungunya, dengue, and Zika virus are all non-native diseases introduced by human activity. The non-native mosquitoes that spread dengue, chikungunya, and Zika virus prefer to feed on humans and breed in man-made habitats. Human impacts on the environment, including land development and climate change, are affecting mosquito habitats and development. Some of these changes to the land, air, and water promote the transmission and spread of mosquito-borne diseases.
By protecting natural environments and their ecological properties and processes, we can help protect ourselves from mosquito-borne diseases – this is One Health in action.
Chikungunya was introduced into the Americas in 2013, with cases in several US territories. Many imported cases have been reported from travelers returning to the US.
Chikungunya only affects humans and is spread by non-native Aedes mosquitoes.
The virus most often causes fever and joint pain in humans 3-7 days after infection, and can also cause other symptoms such as headache, muscle pain, joint swelling, or rash.
Dengue occurs in moist habitats in tropical and subtropical environments worldwide and in the southeastern US, with climate change promoting spread of the disease to the north.
Dengue primarily affects humans and is spread by non-native Aedes mosquitoes.
Dengue causes flu-like symptoms in some people and no visible signs of infection in others.
Zika virus was introduced into the Americas in 2015 and has spread to many US territories, with many imported cases in the US. Only 1 in 5 people infected will get sick.
Symptoms develop 3-14 days after infection and include fever, joint aches, rash, and red eyes. Zika infection during pregnancy can cause miscarriages, brain damage and microcephaly in the fetus. There have also been increased reports of Guillain-Barre syndrome, a paralytic condition, that may be associated with Zika infection.
Zika is spread by non-native Aedes mosquitoes, sexual transmission, and from a mother to fetus. Wildlife do not play a role in maintaining or transmitting the virus.
Eastern Equine Encephalitis (EEE)
Eastern Equine Encephalitis (EEE) is a viral mosquito-borne disease occurring in wooded wetland habitats in the Gulf Coast and Atlantic states and Great Lakes region of the US.
The disease affects humans and animals including birds, horses, and sometimes other mammals including deer.
Most humans do not develop any symptoms of EEE. Less commonly, severe EEE can cause seizures, confusion and life-threatening swelling of the brain in humans.
La Crosse Encephalitis
La Crosse Encephalitis occurs in forests in the Midwestern, mid-Atlantic, and southeastern US.
The disease affects humans and small rodents and is caused by a virus spread by the eastern treehole mosquito (Aedes triseriatus).
La Crosse Encephalitis virus causes no visible signs of infection in most people and flu-like symptoms in some.
Serious cases, most often in children younger than 16 years old, can cause swelling of the brain, which is life threatening and requires emergency medical treatment.
West Nile Virus
West Nile Virus (WNV) occurs throughout the world and is carried by many species of mosquitoes.
The disease is transmitted to humans, birds, and other animals including horses by the bite of infected mosquito.
The majority of infected humans do not develop any symptoms from WNV, although some experience flu-like symptoms and few develop serious neurologic illness.
Birds such as raptors are very susceptible to the disease and often develop severe illness and die. WNV has decreased bird populations in many areas.
Report dead birds to a park ranger as they may indicate that WNV is circulating between birds and mosquitoes.
Western Equine Encephalitis
Western Equine Encephalitis (WEE) is found in grassy, wetland habitats and the plains regions of the western and central US.
The disease affects humans and animals including birds, horses, and sometimes other mammals such as deer.
Most humans do not develop any symptoms of WEE. Less commonly, severe WEE can cause seizures, confusion and life-threatening swelling of the brain in humans.
Biological Resources Division and Office of Public Health
1201 Oakridge Drive, Suite 200
Fort Collins, CO 80525