Tickborne diseases—when a person has been bitten by a tick and gets sick—are increasingly threatening the health of people in the U.S. Tickborne diseases include Lyme disease, anaplasmosis, babesiosis, ehrlichiosis, spotted fever rickettsioses (including Rocky Mountain spotted fever), and tularemia, as shown on the map below. Lyme disease is the most common tickborne illness in the U.S., with an estimated 476,000 Americans diagnosed and treated for Lyme disease and an economic burden between $345 million and $968 million each year (in 2016 U.S. dollars). Early localized symptoms can include a rash at the site of tick bite (occurring in 70–80% of infected persons), fever, chills, malaise, fatigue, headache, muscle aches, joint stiffness, and swelling of lymph nodes. Patients who have Lyme disease are often not even aware of a tick bite before getting sick. Untreated Lyme disease can progress to disseminated disease and produce a wide range of symptoms including additional rashes, facial paralysis, an irregular heartbeat, and arthritis.
Figure: Geographic distribution of select tickborne diseases. For more information, visit the interactive map at https://www.cdc.gov/ticks/data-research/facts-stats/geographic-distribution-of-tickborne-disease-cases.html
Tick bites can also lead to conditions such as alpha-gal syndrome (AGS), a potentially life-threatening allergy to red meat and consumer products made from mammals. Evidence suggests that AGS is primarily associated with the bite of a lone star tick (Amblyomma americanum) in the U.S., but other kinds of ticks have not been ruled out. People with AGS have delayed allergic reactions to a sugar molecule called alpha-gal, which can be found in pork, beef, rabbit, lamb, venison, gelatin, and dairy. Patients with AGS have varying tolerance and sensitivity to products containing alpha-gal, and AGS reactions can vary, ranging from mild to life-threatening. A 2023 CDC report investigating testing data showed that there were more than 110,000 suspected cases of AGS between 2010 and 2022. Additionally, suspected cases are on the rise—from 2017 to 2021, there were approximately 15,000 new positive test results for AGS in the U.S. per year. Another CDC report identified gaps in healthcare provider awareness of AGS, finding 42% of participating healthcare providers had never heard of AGS. Therefore, the number of identified suspect cases of AGS from 2010–2021 is likely an underestimate of the true burden of disease because the diagnosis of AGS requires a clinical exam and a positive diagnostic test.
The Role of Climate Change
Climate change is one of several factors that affect when and where tickborne diseases and tick-associated conditions can occur.
- Increasing temperatures from climate change can influence tick life cycles by increasing a tick’s ability to reproduce. This can lead to larger tick populations and greater risk of germs spreading from tick bites to people.
- Additionally, milder winters and warmer early spring temperatures expand the seasons when ticks are active, resulting in more weeks of the year that people in the U.S. are at risk of tick bites.
- Changing climate patterns can also alter the natural environment and longstanding ecological relationships. The distribution and density of the wildlife ticks feed on (e.g., deer and small mammals) is changing, which can lead to an expanded geographic distribution (e.g., latitude, altitude) of the diseases and conditions associated with these ticks.
- Expanding tick ranges and increasing cases of disease are also linked to changes in land use patterns, such as reforestation, forest fragmentation, and suburban development, which can lead to increased opportunities for humans to be exposed to ticks.
Risk Factors
Risk of tickborne disease varies based on time of year, time spent outdoors in tick habitat, and geographic region.
- Time of year: In areas of the eastern United States where Lyme disease is common, people are most likely to be bitten by blacklegged (deer) ticks during two times of the year: from April through July when nymphs are active, and again from September through November when adults are most active, though people can get bitten any time ticks are present.
- Time spent outdoors: Outdoor workers are at increased risk of tickborne diseases if they work at sites where ticks are common. Worksites with woods, bushes, high grass, or leaf litter are likely to have more ticks. Children ages 5 to 15 years are also at increased risk of tickborne diseases, especially if they play in tick-prone areas.
- Geographic region: Different climates throughout the U.S. support different species of ticks, which spread different diseases. Overall, the geographic range of infected ticks is expanding, putting an increasing number of communities at risk for tickborne diseases. Although the reported nationwide incidence of Lyme disease remained fairly stable from 2008 to 2019 at approximately 11 cases per 100,000 people per year, Vermont, Maine, Rhode Island, Pennsylvania, and West Virginia saw marked increases in Lyme disease incidence over the 10-year period.Data show that the majority of patients with AGS are adults living in the southern, mid-Atlantic, and midwestern regions.
How to Prevent Tickborne Diseases and Conditions
- Protect yourself from bites: Tick bite prevention is the first line of defense against tickborne diseases. Before you go outdoors apply EPA-registered insect repellents, treat clothing and gear with products containing 0.5% permethrin, and talk to your veterinarian about the best tick prevention products for your dog. Check out EPA’s webpage on Using Insect Repellents Safely and Effectively with extra guidance for applying repellents to children. If possible, when spending time outside, avoid wooded and brushy areas with high grass and leaf litter where ticks may live.
- Check for and remove ticks: After spending time outdoors, check your body for ticks, take a shower within 2 hours, and check your clothing, gear, and pets for ticks that may have caught a ride into your home. If you discover a tick on you or your pet, follow the recommended steps for proper tick removal as soon as possible. CDC’s Tick Bite Bot can assist you in removing attached ticks and seeking health care, if appropriate.
- Check your area’s risk: Check the current trends on tick exposure in your region at the CDC transmission website and the Tick Bite Data Tracker, which shows Emergency Department visits for tick bites on a weekly and regional basis. CDC has additional interactive maps displaying tick surveillance data of four tick species and surveillance of tickborne pathogens identified in blacklegged and western blacklegged ticks.
Help your patients: The CDC’s Ticks website and Tickborne Diseases of the U.S.: A Reference Manual for Healthcare Providers have information on specific tickborne diseases including information on how to avoid tick bites, common symptoms, and treatment. CDC has also issued guidance on caring for patients after a tick bite.
Figure. Places to check your body for ticks after being outdoors. Image from CDC.
Figure. How to remove a tick: (1) Use clean, fine-tipped tweezers to grasp the tick as close to the skin’s surface as possible. (2) Pull upward with steady, even pressure. Don’t twist or jerk the tick. (3) After removing the tick, thoroughly clean the bite area and your hands with rubbing alcohol or soap and water. (4) Dispose of a live tick by putting it in alcohol, placing it in a sealed bag/container, wrapping it tightly in tape, or flushing it down the toilet. (5) If you develop a rash or fever within several weeks of removing a tick, see your doctor. Image from CDC.