- Lyme disease is the most common tick-borne illness in the northern United States.
- The tick linked to Lyme disease is localized in the northeast, while other regions experience different diseases.
- In the southern and central United States, spotty fevers spread by various dog ticks pose a higher risk than Lyme.
Tick season typically begins in early spring and lasts through fall in most parts of the United States, causing flu-like illnesses that can have long-term health consequences.
Depending on where you live, the first signs of a tick-borne illness may vary. At least nine different tick species in the United States are capable of spreading the disease, according to surveillance from the Centers for Disease Control and Prevention.
Overall, approximately 50,000 cases of various tick-bite-related illnesses are reported to the CDC each year. Some tick-borne diseases are so rare that there are only a handful of cases reported nationwide each year. Insider has therefore created a map showing the most common tick-borne diseases.
Lyme disease is the most common tick-borne disease in the United States, but the total number of cases is concentrated in areas where the blacklegged tick thrives.
For the purposes of the map, Insider used different scales to describe the incidence of Lyme disease and Rocky Mountain spotted fever, another tick-borne illness. States were considered to have a high incidence of Lyme if they had 100 or more cases per million people in 2019, but the high baseline incidence for spotty fevers was 50 cases per million people. States with fewer than 10 cases per million population for each disease are shown in gray.
Lyme disease is most prevalent in the Northeast and Midwest
Cases of Lyme disease are usually reported in states where the tick species Ixodes scapularis is searching for a host. Also known as the deer tick, this blacklegged tick is native to the Northeast and has spread along the coast and into the Midwest as the climate has warmed.
Maine, Vermont and New Hampshire reported between 800 and 1,200 cases per million people in 2019, which was the most recent year with comprehensive surveillance data compiled by the CDC.
A high number of incidence cases — at least 100 cases per million people — have been reported as far west as Minnesota and along the eastern seaboard. The cases disappear once you travel south to Virginia, where another species of tick is thriving.
Rocky Mountain spotted fever sweeps south, but at lower rates than Lyme
Although less common than Lyme, a tick-borne disease called Rocky Mountain spotted fever sickens thousands of people in the southern United States each year.
Five states – Arkansas, Missouri, North Carolina, Tennessee and Virginia account for more than 50% of spotted fever cases in the United States, according to the CDC. The disease is most common in Arkansas, where more than 350 cases per million people were recorded in 2019.
A few different ticks can spread Rickettsia bacteria, a group that causes spotted fevers. Rocky Mountain spotted fever is the most common illness in the United States, according to the CDC, but most diagnostic tests cannot distinguish between similar bacterial species.
Bites from the American dog tick, brown dog tick, and the geographically named Rocky Mountain wood tick can all cause spotted fevers. The American dog tick is widespread east of the Rockies, while the brown dog tick has spiked RMSF transmission rates in Arizona in recent years.
Some species of ticks can cause several diseases
The blacklegged tick may be known to spread Lyme disease, but it can also transmit bacteria and viruses that cause other illnesses.
The most common of these secondary infections is anaplasmosis, a flu-like illness reported at rates as high as 500 cases per million population in Maine – less than half the incidence of Lyme disease in Maine. state, but higher than most states’ RMSF rates. .
Massachusetts was once a high-incidence Lyme state like its neighbors, but the number of reported Lyme disease cases in the state dropped drastically in 2016. Meanwhile, the rate of anaplasmosis in the state exceeded that of Lyme: same tick, different bacteria.
Ehrlichiosis, another lesser-known tick-borne disease, is spread by the lone star tick in the southern and central United States. In Missouri, the annual rate of ehrlichiosis is almost as high as the rate of RMSF. The disease has been reported as far west as Nebraska, but most cases occur in the eastern half of the country.