The Health Risks of Mosquito Bites: From Itchy Welts to Disease

For most people, a mosquito bite means an itchy bump that fades in a few days. The real health risk comes from the small share of mosquitoes that carry viruses or parasites, such as dengue, West Nile, chikungunya and Zika, and in South Florida those illnesses are not just a travel story: people catch them here every year.

This guide covers the whole range of risks, from skin reactions and infected scratches to the mosquito-borne diseases tracked by the Florida Department of Health. It also explains who is most vulnerable, what the risk means for your pets and when a bite is worth a call to your doctor.

What Happens When a Mosquito Bites You

Only female mosquitoes bite, because they need blood to produce eggs. When a female feeds, she injects saliva into your skin, and your immune system reacts to it. According to the CDC, a typical bite produces:

• A puffy, reddish bump that appears within minutes
• A hard, itchy, reddish-brown bump about a day later
• Sometimes small blisters or dark spots that look like bruises

For a closer look at why that itch happens, read why mosquito bites itch.

Strong Reactions and Infected Bites

Some people react more strongly. The CDC lists children, people with immune system disorders and adults bitten by a mosquito species they have not met before as more likely to develop large areas of swelling and redness, hives, swollen lymph nodes or a low-grade fever.

The other common problem is scratching. Broken skin can become infected, and the CDC lists redness, warmth or a red streak spreading from the bite as signs of infection. To calm a bite, wash it with soap and water, apply an ice pack for about 10 minutes, and use an over-the-counter anti-itch or antihistamine cream according to the label.

The Diseases Mosquitoes Can Spread in Florida

Miami-Dade County alone has more than 50 mosquito species, and only a few of them spread disease. The two groups that matter most around South Florida homes are Aedes mosquitoes, the black-and-white daytime biters that breed in containers, and Culex mosquitoes, brown night biters that breed in drains, ditches and other standing water. Meet them in our guide to mosquito species common to South Florida.

Dengue

Dengue is the mosquito-borne illness Floridians catch most often. The CDC says about 1 in 4 infected people get sick, and about 1 in 20 of those who get sick develop severe dengue, which can cause shock, internal bleeding and death. The dangerous warning signs often start 24 to 48 hours after the fever goes away. Prevention and care are covered in the rise of dengue in South Florida: prevention and treatment.

West Nile Virus

West Nile circulates between birds and Culex mosquitoes and only occasionally infects people. The Florida Department of Health says about 80% of infected people have no symptoms, up to 20% have a mild illness, and about 1 in 150 develop severe illness, with high fever, neck stiffness, disorientation, tremors, convulsions or paralysis. Symptoms usually appear 3 to 14 days after the bite, and some neurological effects may be permanent. See West Nile virus in South Florida for more.

Chikungunya

Chikungunya rarely kills, but it can be miserable. The CDC says symptoms usually begin 3 to 7 days after the bite, and the joint pain can be severe, disabling and last for months, even though most people feel better within a week overall. Florida reported a locally acquired case in Miami-Dade in 2026.

Zika

Many people infected with Zika have no symptoms or only mild ones that last several days to a week. The concern is pregnancy: the CDC says Zika infection during pregnancy can cause serious birth defects and is linked to fetal loss, stillbirth and preterm birth. Zika can also trigger Guillain-Barré syndrome, a rare nerve disorder that causes muscle weakness. Florida reported no Zika cases in 2026 through mid-October, but the Aedes mosquitoes that spread it are still common here.

Eastern Equine Encephalitis, St. Louis Encephalitis and Malaria

Eastern equine encephalitis (EEE) is rare but serious. The CDC says about 30% of people who develop severe EEE die, and many survivors have lasting neurological problems. St. Louis encephalitis is spread in the southern half of Florida mainly by Culex nigripalpus, which was the key mosquito in the state’s SLE epidemics from 1959 to 1990, according to UF/IFAS.

Malaria is usually brought in by travelers, but local transmission can happen. In 2023, Florida had 7 locally acquired malaria cases in Sarasota County, the first local cases in the United States since 2003 in Palm Beach County, according to the CDC.

How Common Are Mosquito-Borne Illnesses in Florida?

The Florida Department of Health publishes weekly arbovirus surveillance reports. Here is what it counted statewide in 2026 through October 17:

South Florida carries a large share of the travel-related cases: Miami-Dade alone reported 200 of the 320 travel-associated dengue cases and 54 of the 88 chikungunya cases. As of mid-October 2026, Miami-Dade was under a mosquito-borne illness alert, and Broward and Palm Beach were under an advisory. Every imported case is a chance for local Aedes mosquitoes to pick up the virus and start a cluster, which is how locally acquired dengue keeps appearing in Florida. Read more in are Floridians at risk for dengue fever.

Who Faces the Greatest Risk From Mosquito Bites?

Anyone can be infected, but some people are more likely to become seriously ill:

• Adults over 50: more likely to develop serious West Nile symptoms, per the Florida Department of Health.
• Adults 65 and older and newborns: at higher risk of severe chikungunya, along with people who have high blood pressure, diabetes or heart disease (CDC).
• Pregnant women: Zika can harm the baby. The Florida Department of Health encourages pregnant and nursing women to talk to a doctor about possible West Nile symptoms too.
• People who have had dengue before: the Florida Department of Health names a previous infection with a different dengue type as the main risk factor for the severe form.
• People who spend a lot of time outdoors: landscapers, construction workers and anyone outside at the peak biting hours have more exposure.

Mosquito Bites and Your Pets

Mosquitoes are a health risk for dogs and cats too. According to UF/IFAS, dogs get heartworm through mosquito bites. A mosquito picks up tiny larvae from an infected dog, the larvae develop inside it for roughly two to three weeks, and the next bite passes them on. Of the 16 mosquito species that naturally host dog heartworm east of the Mississippi, 11 are found in abundance in Florida, and because mosquitoes are active all year here, the threat is constant.

Cats are less often infected but not immune, and UF/IFAS notes that even indoor cats have been infected. There is no approved treatment for feline heartworm in the United States, so prevention matters. Ask your veterinarian about a year-round preventive; only a vet can choose the right product and dose.

When to See a Doctor After Mosquito Bites

Most bites need nothing more than ice and an anti-itch cream. Call a healthcare provider when:

• A bite shows signs of infection: spreading redness, warmth or a red streak
• You have a large or worsening reaction, hives or swollen lymph nodes
• You develop a fever, severe headache, eye pain, rash or joint pain within about two weeks of bites, especially after travel or during a local alert
• You are pregnant and may have been exposed to Zika during travel

How to Lower the Health Risk Around Your Home

You cannot avoid every mosquito in South Florida, but you can make bites much less likely. The Florida Department of Health’s Drain and Cover approach is the foundation:

1. Drain standing water. Empty buckets, coolers, toys and flowerpots after rain, and empty and scrub birdbaths and pet bowls once or twice a week.
2. Cover your skin. Use an EPA-registered repellent with DEET, picaridin, IR3535, oil of lemon eucalyptus, para-menthane-diol or 2-undecanone, following the label. Use mosquito netting for babies younger than 2 months.
3. Cover doors and windows. Repair torn screens on windows, doors, porches and patios.

Because Aedes mosquitoes bite during the day and Culex mosquitoes bite at night, protection has to cover both. When draining and screening are not enough, Toro’s mosquito control service starts with a free inspection to find where mosquitoes breed and rest on your property, then treats the shrubs where adults rest and the breeding sites where larvae develop. Toro has protected homes and businesses across Miami-Dade, Broward, Palm Beach and the Keys since 1969, and if the bugs come back, so will Toro, at no additional cost to you.

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Frequently Asked Questions

Educational content. This article is for general information about pests in South Florida and is not medical, legal or professional advice. If you have a bite, sting or allergic reaction, contact your doctor; in an emergency, call 911. Pest problems vary from home to home, so a licensed professional should inspect before treatment. When using any pesticide, always read and follow the product label.

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