Every year from mid-spring to mid-summer, reports of tick bites rise. Although Lyme disease is the most well-known and most common tick-borne disease, there are others to be aware of.
What is Lyme Disease?
Lyme disease is the most common vector-borne disease in the US — that is, spread via blood-feeding insects like fleas, ticks, and mosquitoes. Symptoms include headache, fatigue, fever, and a skin rash. If untreated, the disease can spread to the heart, joints, and nervous system. In most cases, it can be successfully treated with antibiotics.
How common is Lyme Disease?
Although it’s difficult to know exactly how many people are infected every year, the Centers for Disease Control and Prevention (CDC) estimates that around 476,000 people are diagnosed and treated for Lyme disease annually. The agency based this number on insurance claims from 2010–2018 — and it may be an overestimate due to people receiving treatment when they weren’t actually infected.
The number of reported cases in 2022 was 63,000 or nearly 19 in 100,000 people. This is an increase from 2018’s 7.21 in 100,000 people.
Why are estimates and reported cases so different? This is partly because reporting is not required, and what is reported varies by health department. Many cases are never reported because they're diagnosed and treated without lab testing.[1]
The CDC attributes increasing tick-borne diseases to changes in land use — suburban development has introduced people into areas where ticks are more likely to live. It also notes that changing climate patterns impact the locations and seasonality of tick bites.
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How many people contract tick-borne diseases each year?
From 2016–2022, there were around 48,500 reported cases of tick-borne diseases per year. Total reported cases dropped in 2020 and 2021 due to incomplete agency reporting during the COVID-19 pandemic. The criteria for reporting cases of Lyme disease changed in 2022, which increased the number of reports that year.
What other diseases are caused by tick bites?
Lyme disease accounted for nearly 75% of all reported tick-borne disease cases from 2016–2022. Of the remaining quarter, Spotted fever rickettsiosis made up 10% and anaplasmosis 7%. The remaining 8% includes all other tick-borne diseases.
The CDC lists fifteen known tick-borne diseases in the US. It tracks reports for Lyme disease and the six other most-occurring tick-borne diseases:
A group of diseases all caused by the same bacteria. Rocky Mountain Spotted Fever (RMSF) is the most common and serious of the spotted fevers and occurs across the US. Symptoms can include headache, fever, nausea and vomiting, stomach pain, muscle pain, and a rash. RMSF typically doesn’t result in long-term health problems.
A disease caused by microscopic parasites that infect red blood cells. Some people may not experience symptoms, but they can include fever, chills, head and body aches, loss of appetite, fatigue, and nausea. It is treatable if diagnosed.
Symptoms can begin 1-2 weeks after being infected by a tick and can include fever and chills, muscle and head aches, nausea and gastrointestinal distress, and a rash. It is treatable with antibiotics.
Early symptoms can include fever and chills, head and muscle aches, nausea, vomiting, diarrhea, and loss of appetite and can be treated with antibiotics. If left untreated, the late-stage illness can progress to respiratory failure, bleeding problems, organ failure, and death.
Common symptoms of tularemia, when transmitted via a tick bite, include swelling of regional lymph glands, which are sometimes accompanied by an ulcer. This disease is rare and can be difficult to diagnose but can be treated with antibiotics.
Early symptoms can include fever, vomiting, headache, and weakness, and can progress to infection in the brain, or of the membranes around the brain and spinal cord, which can cause seizures, difficulty speaking, and confusion. Currently, there is no medication or treatment.
Where is Lyme disease most common?
Lyme disease cases are reported most often in Northeastern states. Pennsylvania had 29.2% of all reported cases from 2016–2019. New Jersey followed with 11.7%, and New York reported 11.6%. Seven of the 10 counties most affected by Lyme disease are in Pennsylvania.
Conversely, Hawaii reported zero cases from 2016–2019, in part due to surveillance data limitations.
What other areas are at high-risk areas for tick-borne diseases?
Between 2016 and 2019, spotted fever rickettsiosis cases were reported most in in Arkansas (21.6% of cases), Alabama (12.1%), North Carolina (11.6%), and Tennessee (10.6%). Zero cases were reported in Alaska and Hawaii.
In that same timeframe, the most instances of anaplasmosis were reported in New York (31.7% of cases), Wisconsin (14.6%), and Vermont (10.1%). Zero cases were reported in South Carolina, Georgia, Idaho, Colorado, New Mexico, Alaska, and Hawaii.
How many people go to the emergency room for tick bites?
On average, a reported 533 people per year went to the emergency room for tick bites from 2017–2023.[2]
Tick bite-related ER visits are highest on average from April to July, peaking in May at an average of 119. They drop in August and September, and spike again in October and November.
Where do ticks live?
Tick species inhabit nearly all regions of the United States, with varying concentrations depending on the species and location.
The blacklegged tick and the western blacklegged tick — the two species that carry the bacteria that cause Lyme disease — are concentrated on the eastern half of the United States and the Pacific coast.[3] The blacklegged tick is linked to pathogens that can cause Lyme disease, as well as anaplasmosis, tick-borne relapsing fever, ehrlichiosis, babesiosis, and Powassan virus disease. The western blacklegged tick is linked to pathogens which can cause Lyme disease, anaplasmosis, and tick-borne relapsing fever.
The CDC also tracks data for five other tick species that do not carry Lyme disease:
- The American dog tick, primarily found east of the Rocky Mountains and in areas of the Pacific coast.
- The brown dog tick, which is found worldwide.
- The Gulf Coast tick, which is found along the Atlantic coast and the Gulf of Mexico.
- The lone star tick, which is found in the eastern, southeastern, and south-central United States.
- The Rocky Mountain Wood Tick, which is found in the Rocky Mountain states (eastern Washington, eastern Oregon, parts of northeastern California, Nevada, Idaho, Utah, Montana, Wyoming, and Colorado).
The CDC provides recommendations to prevent tick bites, prevent ticks on pets, and limit tick presence in yards surrounding homes. Most tick-borne diseases are treatable, especially if caught early.
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[1] Lyme disease surveillance and available data is limited because not every case of Lyme disease is reported to the CDC, and some reported cases may have another cause. Surveillance data are captured by county of residence, not county of exposure.
[2] CDC emergency room tick bite data from the National Syndromic Surveillance Program (NSSP) is aggregated through private sector partners, and local and state health departments. There may be reporting differences between regions, and tick bite visits are aggregated based on ICD diagnostic codes.
[3] Tick tracking is done via CDC ArboNET, which is a passive surveillance system that relies on jurisdictions to voluntarily collect and report non-human, vector-borne infection and ecologic data. Tick presence may not be representative of pathogen/disease presence.
