The West Nile virus is the most common mosquito-borne illness in California. While many people experience mild or no symptoms, it can lead to severe neurological conditions such as encephalitis (brain inflammation) or meningitis.

Zika virus, though less common in the U.S., is a major concern for pregnant women, as it can cause serious birth defects like microcephaly, where a baby’s head is significantly smaller due to brain underdevelopment.

St. Louis encephalitis is a rare but potentially severe disease that can cause headaches, fever, confusion, and in serious cases, long-term brain damage or death, especially in older adults or those with weakened immune systems.

The presence of invasive mosquito species like Aedes aegypti increases the risk of these viruses spreading locally, even from people who recently traveled abroad.

Most people experience itchy, red welts shortly after being bitten. This reaction is due to the mosquito’s saliva, which triggers the body’s immune response.

Some individuals, especially children or those with allergies, may suffer from exaggerated reactions, including swelling, rash, or blistering.

Scratching can lead to skin breaks that become infected, especially if hygiene is poor or bites are repeatedly irritated.

In rare cases, people may experience skeeter syndrome, a more severe allergic reaction involving fever, swelling, and joint pain at the bite site.

The most common threat is heartworm disease, caused by a parasite transmitted through mosquito bites.

Once inside a pet's body, the heartworm larvae grow into long worms that inhabit the heart, lungs, and blood vessels, leading to lung disease, heart failure, and even death if not treated.

Heartworm is particularly dangerous because symptoms often appear late, when damage is already done. Prevention with monthly medication is the best defense.

Outdoor pets or those in mosquito-heavy areas are especially vulnerable and should be protected with both veterinary-recommended preventatives and environmental mosquito control.