8 Common Illnesses From Tick and Mosquito Bites

Insect-borne illnesses in the U.S. have surged, with cases more than doubling between 2001 and 2023, according to the CDC. Dr. Beth Kirkpatrick, an infectious disease specialist at the University of Vermont Medical Center, warns of growing risks, including ticks carrying multiple pathogens—an *Ecosphere* 2025 study found about 1 in 10 juvenile deer ticks in the Northeast U.S. harbor two or more disease-causing germs. Climate change and human land-use changes are key drivers. Milder winters allow ticks to survive longer, while suburban sprawl boosts populations of mice, deer, and chipmunks—animals that host ticks. Global travel also introduces rare infections like chikungunya and Zika. Lyme disease remains the most common insect-borne illness in the U.S., with over 89,000 cases reported in 2023 and estimates suggesting up to 476,000 annual diagnoses. Transmitted by infected deer ticks (*Borrelia burgdorferi*), it has expanded geographically, now common in the Midwest and Eastern Seaboard. Symptoms include a bull’s-eye rash, fatigue, and joint pain, treatable with antibiotics. A Pfizer-Valneva vaccine in phase 3 trials showed 70% efficacy. West Nile virus, the most common mosquito-borne disease, peaked in late 2025 with 2,076 U.S. cases. Spread by infected culex mosquitoes, it cannot be transmitted human-to-mosquito. Other notable illnesses include Eastern equine encephalitis, Zika, and chikungunya, with varying symptoms and no widely available vaccines for most. Prevention focuses on avoiding bites—using repellents, wearing protective clothing, and removing standing water. Early antibiotic treatment for Lyme disease improves recovery rates, though post-treatment symptoms can persist. Public health experts emphasize monitoring trends as climate and land-use shifts worsen transmission risks.