Banner Health
Making healthcare easier

Mosquito-Borne Illnesses in the U.S.

Infected mosquitoes transmit mosquito-borne diseases to humans through their bites. These tiny insects can carry a variety of pathogens, including viruses and parasites, which can cause serious health complications. In the United States, several mosquito-borne illnesses pose a risk to public health, with West Nile Virus being one of the most common. 

You can lower your risk of infection by learning about the dangers of these diseases. Taking steps to prevent mosquito bites is also important.

West Nile virus (WNV)

What is West Nile virus?

The West Nile virus (WNV) is a virus transmitted by mosquitoes that belongs to the flavivirus genus. It typically occurs in Africa, West Asia and the Middle East. The virus was first identified in the United States in 1999 and has since become a significant public health concern.

How is West Nile virus transmitted and spread?

Infected mosquitoes, particularly species of the Culex genus, primarily transmit WNV to humans through their bites. Mosquitoes pick up the virus from infected birds. Then, they spread it to people and other animals when they bite.

Symptoms and risk factors of West Nile

Most individuals infected with WNV do not develop any symptoms. About 20% of people who get sick may experience mild symptoms such as fever, headache, body aches, nausea and vomiting. These symptoms are known as West Nile fever. 

In severe cases, WNV can lead to brain inflammation (encephalitis) or inflammation of the brain and spinal cord lining (meningitis). Older adults and individuals with weakened immune systems are at higher risk of developing severe illness from WNV.

How to prevent West Nile virus

Preventing mosquito bites is the most effective way to reduce the risk of WNV infection. 

Here are some preventive measures:

  • Use insect repellents containing DEET, picaridin or oil of lemon eucalyptus.
  • Wear long-sleeved shirts, long pants and socks when outdoors, especially during dawn and dusk when mosquitoes are most active.
  • Install or repair screens on windows and doors to keep mosquitoes out of your home.
  • Remove standing water from containers around your home to eliminate mosquito breeding sites.
  • Use mosquito nets over cribs, strollers and outdoor sleeping areas for infants and young children.

Treatment options and prognosis for West Nile

There is no specific antiviral treatment for WNV infection. You can manage mild symptoms with over-the-counter (OTC) medications to reduce fever and help with pain. Severe cases may require hospitalization for supportive care, including intravenous (IV) fluids, respiratory (breathing) support and medications to reduce brain swelling. 

The outlook for people with severe WNV complications differs. Some may have lasting neurological issues. Detecting the illness early and providing support can help improve outcomes for those with severe symptoms.


What is encephalitis?

Encephalitis is a rare but serious condition characterized by inflammation of the brain. Various factors, including viral infections like those transmitted by mosquitoes, can cause it. 

Encephalitis can cause a range of neurological symptoms, from mild to severe. These symptoms may include fever, headache, confusion, seizures, and in severe cases, coma. 

Various strains of encephalitis include:

La Crosse encephalitis (LAC)

La Crosse encephalitis (LAC) is a virus primarily transmitted to humans who are bitten by an infected mosquito, particularly the Aedes triseriatus species. LAC virus is commonly found in the upper Midwestern and Mid-Atlantic regions of the United States.

Symptoms and risk factors of LAC

LAC infection can cause symptoms such as fever, headache, nausea, vomiting and fatigue. In severe cases, individuals, particularly children, may develop encephalitis, leading to neurological complications. Children under the age of 16 are at higher risk of severe illness from LAC.

How to prevent LAC

You can prevent LAC by reducing your exposure to mosquito bites. You can do this by wearing insect repellent, wearing long-sleeved clothing and using mosquito nets. Eliminating places where mosquitoes breed and using larvicides are important in stopping the spread of the LAC virus.

Eastern Equine encephalitis (EEE)

Eastern Equine encephalitis (EEE) is a rare but severe mosquito-borne illness caused by the EEE virus. The virus is mainly spread to humans through the bite of infected mosquitoes, especially those in the Culiseta melanura group. The EEE virus goes back and forth between birds and mosquitoes. Humans and horses are considered dead-end hosts, meaning they can't spread the virus further.

Symptoms and risk factors of EEE

EEE infection can result in severe symptoms, including high fever, headache, stiff neck, and neurological complications such as encephalitis. 

Severe cases of EEE can be fatal, with a mortality rate of approximately 30% among those who develop encephalitis. EEE infection can affect people of all ages. However, it is more serious in infants and older adults.

How to prevent EEE

To prevent EEE, you should take the same precautions as you would for other mosquito-borne illnesses. 

  • Use insect repellent.
  • Stay indoors during peak mosquito hours (dusk and dawn).
  • Eliminate standing water around your home to prevent mosquito breeding.
  • Vaccinate horses (if applicable) to help reduce EEE transmission risk to humans.

Jamestown Canyon virus (JCV)

Jamestown Canyon virus (JCV) is a rare virus spread by mosquitoes. It belongs to a group of viruses called the California serogroup. This group is in the Orthobunyavirus genus.

The virus is usually found in forests and near water where mosquitoes breed. JCV has been reported in various regions of the United States, including the Northeast, Midwest and West Coast.

Symptoms of JCV

Infection with JCV can result in mild symptoms such as fever, headache, and muscle aches. In rare cases, individuals may develop encephalitis or meningitis. 

How to prevent JCV

To avoid JCV, do the same things you would do to prevent other illnesses spread by mosquitoes. Use bug spray, wear protective clothing and get rid of any places where mosquitoes can breed close to your house.

Less common mosquito-borne illnesses

West Nile Virus and encephalitis are well-known mosquito-borne illnesses. However, there are other lesser-known illnesses transmitted by mosquitoes. Dengue fever, chikungunya Virus and Zika virus are each different and bring their own set of factors to consider.

These illnesses are not as common in the United States as in other regions. However, they can still have a big impact on individuals and communities. This is especially true in areas where the right kind of mosquitoes are present. 

Understanding how diseases spread, recognizing their symptoms and knowing prevention methods are important for public health and personal safety. 

Dengue fever

What is dengue fever?

Dengue fever is caused by a virus spread through mosquito bites. The mosquitoes that spread the virus are Aedes aegypti and Aedes albopictus. People get sick with dengue fever when they are bitten by these mosquitoes. 

Dengue viruses are found in many tropical and subtropical regions worldwide. Some parts of the United States, such as Florida, Texas, and Hawaii, also have dengue viruses.

Symptoms of dengue fever

Symptoms of dengue fever may include high fever, severe headache, pain behind the eyes, joint and muscle pain, rash and mild bleeding. Outbreaks can happen in states with mosquito-friendly environments. This is especially true in the warmer months.

How to prevent and treat dengue fever

To avoid getting dengue fever, you can take steps to limit your contact with mosquitoes. This includes using insect repellent, wearing long sleeves and eliminating any stagnant water where mosquitoes breed. 

There is currently no specific antiviral treatment for dengue fever. The goal of treatment is to relieve symptoms and avoid complications.

Chikungunya virus (CHIKV)

What is Chikungunya virus?

Chikungunya virus is another mosquito-borne illness transmitted primarily by Aedes mosquitoes. The virus was first found in Africa and has now spread to many parts of the world, including the Americas. Chikungunya virus causes fever and severe joint pain, among other symptoms.

Symptoms of CHIKV and affected areas in the U.S.

Symptoms of chikungunya virus infection may include fever, joint pain, muscle pain, headache, nausea, fatigue, and rash.

Chikungunya cases in the continental United States mostly come from travelers returning from affected regions. Some cases have also been reported within the country.

How to prevent Chikungunya virus

To avoid Chikungunya virus, use insect repellent. Wear long-sleeved clothing in areas where the virus is present. Use mosquito nets for added protection. Eliminating mosquito breeding sites around homes and communities also helps prevent transmission.

Zika virus

What is Zika virus?

Zika is a mosquito-borne virus similar to yellow fever and West Nile virus. The virus spreads mainly through the bite of an infected Aedes mosquito (Aedes aegypti and Aedes albopictus species). Zika can also be passed through unprotected sex with someone infected with Zika or from an infected pregnant person to their baby. 

Symptoms and impact of Zika, particularly on pregnant women

Symptoms of Zika virus infection are usually mild and may include fever, rash, joint pain, and conjunctivitis (pink eye). However, Zika infection during pregnancy can lead to serious birth defects. These can include microcephaly (a condition where a baby's head is significantly smaller than expected for their age and sex) and other neurological complications, in the developing fetus.

Prevention and precautions for travelers

Prevention of Zika virus infection involves using insect repellent, wearing protective clothing and practicing safe sex to prevent transmitting from person to person. Pregnant women and those planning pregnancy should avoid travel to areas with ongoing Zika transmission. Travelers to affected regions should take precautions to prevent mosquito bites and reduce the risk of Zika infection.

Key points

It's important to know how illnesses are spread, what their symptoms are and how to prevent them. This will help you and others stay safe from getting sick. Controlling mosquitoes is important for preventing the spread of diseases they carry, at both community and individual levels.

To avoid mosquito bites and lower the chance of getting sick, you should get rid of any standing water. You should also use bug spray, wear protective clothing and use other ways to prevent mosquito bites.

If you experience symptoms such as fever, headache, muscle aches, rash, or any other unusual signs after being bitten by mosquitoes, seek medical care immediately. Early diagnosis and treatment can help manage symptoms and prevent complications, particularly in cases of severe illness such as encephalitis or complications during pregnancy. 

BH Icon Urgent_Care_White

Patient Account

Access your health information anytime, anywhere. Your Patient Account allows you manage your care from any device so you can: view lab results, request medical records, book appointments, message a doctor’s office and access important documents. 

Sign In