The black-legged tick transmits anaplasmosis in Tennessee.
Anaplasmosis under a microscope

Anaplasmosis is a tick-borne disease caused by the bacteria Anaplasma phagocytophilum. In Tennessee, it is transmitted by Ixodes scapularis, also known as the black-legged or deer tick.

Cases of anaplasmosis have been on the rise in our state since 2014, however, in 2023 there was a significant decrease, with only 1 case being reported, compared to 14 cases in 2022. These cases, typically occurring throughout all regions of Tennessee, are an emerging concern attributed to the expanding distribution of black-legged ticks.

For more information about this disease, see the CDC's Anaplasmosis Home Page.

The gradient on the map below refers to average anaplasmosis incidence rates for each county in Tennesee from 2013-2023, which was calculated using county population data from the 2020 U.S. Census.

From 2013-2023, there was an average of 2 cases per county reporting positive Anaplasma infections. Dickson County reported 12 anaplasmosis cases (or 12% of all reported cases) during that time.

Anaplasmosis case map across Tennessee by county

In Tennessee, illness onset for cases of anaplasmosis is mainly reported in the warmer months of the year. The number of reported anaplasmosis cases is lowest in the winter (December-February), slightly increases in the spring (March-May), peaks in the mid to late summer (June-September), and then gradually declines through autumn (October-November).

67% of anaplasmosis cases occur in the mid to late summer months between June and September.

Signs and symptoms of anaplasmosis typically begin 5-14 days after being bitten by an infected black-legged tick. Therefore, late spring through mid summer is the time of year when Tennesseans are most at risk for contracting anaplasmosis.

Anaplasmosis cases by onset week
Note: The n=68 in this chart refers to reported cases of anaplasmosis from 2013-2023 with recorded illness onset dates. Thus, this figure only accounts for a portion of the total number of anaplasmosis cases reported during this time period.

Anyone who spends time outdoors in Tennessee is at risk of contracting anaplasmosis, because the black-legged tick that spreads this disease is most often found in wooded, brushy areas. People holding outdoors-based occupations, such as farmers and landscapers, may be at increased risk of getting bitten by an infected tick, as are people who regularly hike, camp, hunt, or garden in or around wooded areas.

Black-legged ticks may also dwell in the property surrounding Tennessee homes, especially if your yard is either next to a brushy area or has tall grass and/or leaf litter. Even outside of our state's forests, it is important to take the necessary steps to prevent tick bites in any environment habitable by black-legged ticks.

Individuals of any reported gender, sex, and age group in Tennessee can get sick with anaplasmosis. However, most cases of anaplasmosis are reported in residents between the ages of 35 and 70.

Anaplasmosis cases by age group and reported sex
Anaplasmosis cases by year and hospitalization status

Signs and symptoms of anaplasmosis typically develop within 1-2 weeks after being bitten by an infected tick. Early signs and symptoms (days 1-5) are usually mild or moderate, and they may include:

  • Fever and/or chills
  • Severe headache
  • Muscle aches
  • Nausea, vomiting, diarrhea, or loss of appetite

If treatment is delayed or if there are other medical conditions present, anaplasmosis can, in rare cases, cause severe illness. Late stage signs and symptoms can include:

  • Respiratory failure
  • Bleeding problems
  • Organ failure
  • Death

For more information, see the CDC's Anaplasmosis Signs and Symptoms web page.

Anaplasmosis is diagnosed by a healthcare provider, who can order blood tests to look for evidence of Anaplasma infection. It may take several weeks for test results to return. If your provider is concerned, they may prescribe you with antibiotics while you wait for the results.

For more information, see the CDC's Anaplasmosis Diagnosis and Testing web page.