Keep mosquitoes from spoiling your summer fun and health

They’re here – those warm, sunny days that invite long walks in the woods, dining al fresco and sitting by the water’s edge. But people aren’t the only ones who flock to the great outdoors each summer. Mosquitoes – attracted to the same forests and bodies of still water that people enjoy – may decide to join the party for a quick bite.

Most mosquitoes are little more than a nuisance. But some will leave behind more than an itchy welt.

Mosquitoes can carry germs that sometimes cause serious illnesses. Unfortunately, experts say, it can be tough to differentiate potentially dangerous, even fatal, mosquito-borne illnesses from more common viruses.

“The majority of mosquito-borne diseases will present like flu,” said Dr. Melissa Nolan, an associate professor of epidemiology and director of the Institute for Infectious Disease Translational Research at the University of South Carolina in Columbia. “And most doctors won’t test for these, so you have to be your own advocate.”

According to the Centers for Disease Control and Prevention, there are more than 200 types of mosquitoes in the U.S. and its territories, most of which are nothing more than unwelcome pests. But 12 types of mosquitoes carry the germs that can make people sick.

In the U.S., there are three major mosquito-borne diseases, said Nolan, who also is deputy director of the Southeastern Center of Excellence in Vector-Borne Diseases.

“West Nile virus is the most commonly reported nationally,” she said. While less common, two others – eastern equine encephalitis, or EEE, and La Crosse encephalitis – are serious and can result in severe illness or death.

“There are no treatments for any of these,” Nolan said. “It’s all about prevention.”

West Nile virus

West Nile virus first appeared in the U.S. in 1999, and nearly 61,000 human cases have been reported through 2024, according to the CDC. Just 33 cases have been reported in 2025. The virus is initially transmitted to birds or small mammals, then mosquitoes that feed on their blood can transmit the virus to humans.

People infected with West Nile likely don’t feel sick, but according to the CDC, approximately 1 in 5 will develop a fever and other symptoms. About 1 in 150 infected people may develop severe illness affecting the central nervous system, such as encephalitis – inflammation of the brain – or meningitis, which is inflammation of the membranes surrounding the brain and spinal cord. About 1 in 10 people who develop severe illness will die.

Age can play a role in illness severity, Nolan said.

“If everyone in the family got bitten by a mosquito carrying West Nile, the person most likely to get severe disease would be the older adult,” she said.

That’s because older adults tend to have weaker immune systems than younger people and are more likely to have other conditions that put them at higher risk, such as high blood pressure or diabetes. People who have cancer, kidney disease or who have received organ transplants also are at greater risk for severe illness.

Symptoms include high fever, headache, neck stiffness, disorientation, convulsions, muscle weakness, vision loss, tremors, numbness and paralysis or coma. It can take weeks or months to recover, though some effects of the disease may be permanent.

While there are no treatments for West Nile, supportive treatments – such as IV fluids and pain medication – may be given to ease symptoms, Nolan said.

La Crosse encephalitis

La Crosse encephalitis is transmitted by mosquitoes in the upper Midwestern, mid-Atlantic and Southeastern states, especially along the Ohio River Valley, Nolan said.

In contrast to West Nile, severe illness from La Crosse encephalitis disproportionately occurs among the very young. While most people who get infected experience no symptoms at all, severe illness is most common among children under 16.

Common symptoms may include fever, headache, seizures, vomiting, confusion and fatigue. When severe, the symptoms may indicate encephalitis.

Eastern equine encephalitis

Only a few cases of EEE in humans are reported in the U.S. each year, mostly in eastern or Gulf Coast states.

Like West Nile virus, EEE can affect the brain. About 30% of people who develop severe illness die, and those who don’t may have permanent neurological problems. Symptoms include fever, headache, vomiting, diarrhea, seizures, behavioral changes and drowsiness.

In August 2024, officials in Plymouth, Massachusetts, closed outdoor recreation facilities from dusk until dawn each night after a horse was infected with EEE, and an 80-year-old man in another part of the state contracted the virus.

Other mosquito-borne illnesses in the U.S.

Malaria – no longer common in the U.S. – most often is seen when people return home infected after traveling to areas where it’s endemic. There have been occasional outbreaks within the U.S., Nolan said, including one in 2023 when locally transmitted cases occurred in Maryland, Florida and Texas.

While much more common in tropical countries, dengue, chikungunya and Zika outbreaks have also occurred in the U.S. Other, rarer mosquito-borne illnesses that can occur in the U.S. include Cache Valley, Jamestown Canyon virus and St. Louis encephalitis.

Even when viruses are not endemic to the U.S. or Canada, people who visit or emigrate from other countries may bring illnesses back with them, said Dr. Adrian Baranchuk, a professor of medicine at Queens University in Kingston, Ontario, and president of the Inter-American Society of Cardiology.

Anyone who develops symptoms after being in an area where mosquito-borne illnesses are prevalent should immediately bring this to the attention of their health care team, he said.

Mosquito-borne illnesses and heart health

While severe cases of West Nile, EEE and La Crosse are more likely to affect the brain, malaria and dengue are most frequently associated with heart disease.

Both malaria and dengue can strain the cardiovascular system by damaging blood vessels or the cells that line them, making it harder for the heart to deliver oxygen to the rest of the body, Nolan said. “And this puts the person at greater risk for heart failure or a heart attack.”

Though rare, severe illness from malaria or dengue also can lead to myocarditis, an inflammation of the heart muscle, Baranchuk said. It may also be accompanied by abnormally fast heart rhythms called tachycardia, or by bradycardia, which occurs when the heart isn’t pumping hard enough.

“These cases can be very difficult to treat and can be fatal,” he said.

Testing for an infection

Since a variety of illnesses can cause flu-like symptoms, it can be tough to know when a person has been infected with a serious mosquito-borne illness such as West Nile, Nolan said.

“It takes a few days to get sick after you’ve been bitten,” she said. “You may have a headache, fever, or generally just don’t feel well. The best thing to do, especially if you have other risk factors for severe illness, is to try to get to a doctor early.”

Nolan said it may be necessary to ask for tests to identify if a mosquito-borne illness is present if a doctor does not order one.

How to protect yourself

Since it’s impossible to know whether a mosquito bite comes from an infected insect, the CDC recommends people take steps to protect themselves and their children from exposure.

Staying away from areas where mosquitoes live, especially during peak feeding hours – including dawn and dusk – is one way to prevent being infected, Nolan said.

Mosquitoes thrive at temperatures above 70 degrees Fahrenheit. Depending on the location, mosquito season takes place during summer and fall, though it may begin as early as spring. Some mosquitoes like living near people, while others prefer to inhabit areas with forests, marshes and tall grasses. They may lay their eggs near the edges of lakes and ponds, among wetland plants and even in containers that fill up with rainwater. But they can also live in warm, urban areas, where they may breed in stagnant water. According to pest control reports, the U.S. cities with the largest mosquito populations include Los Angeles, Dallas-Fort Worth, New York and Atlanta.

Nolan said an integrated pest management strategy can help. In addition to avoiding peak feeding times and places, she suggested wearing long sleeves, using mosquito repellents, and spraying areas used for family gathering, such as backyards and patios.

Products that contain DEET or permethrin, which also protects against ticks, are very effective at keeping mosquitoes at bay, she said. People who prefer natural remedies may use products made from lemon eucalyptus.

“There are better and worse repellents,” Baranchuk said. “But the worst is no repellent.”

Nolan also recommended that people “tip and toss” any water sources where mosquitoes may lay eggs, such as bird baths or watering cans sitting outdoors. Fogging a yard with repellent can also be effective.

“But you don’t have to spray the entire yard, just the areas where you are going to be sitting outside at night,” she said.