Vector-Borne Diseases

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

In 2023, WNV activity increased as compared to previous years, with a total of 9 human cases. Five of these cases occurred in Shelby County, and single cases also occurred in Davidson, Hamblen, Rutherford, and Williamson Counties. 

There were also 1 WNV positive equine case in 2023, which occurred in Gibson County. WNV positive mosquito pools were detected in all 3 counties where mosquito trapping was conducted; Davidson, Shelby, and Knox Counties.

In Tennessee, illness onset for cases of WNV is mainly reported in the second half of the year. The number of reported WNV cases is lowest in the winter (December-March), slightly increases in the late spring to mid-summer (April-July), peaks in the late summer (August-September), and then gradually declines through autumn (October-November).

Signs and symptoms of WNV typically begin 1-2 weeks after being bitten by an infected mosquito. Late spring through mid-summer is the time of year when Tennesseans are most at risk for contracting WNV.

Anyone who spends time outdoors in Tennessee is at risk of contracting WNV. However, persons over 50 years of age are at highest risk of developing the most severe form of the disease, and persons over the age of 70 with pre-existing health problems are at greatest risk for death.

In regards to trends over the past decade, case numbers for WNV have risen in 2023, compared to recent previous years. The dip in cases seen in 2020 can be identified in vector-borne diseases across the board during that year, likely due to a number of factors surrounding the COVID-19 pandemic.

Most people infected with WNV do not devleop any symptoms. About 1 in 5 people who are infected will develop a mild febrile illness, which includes a fever in addition to one or more of the following symptoms:

• Headache
• Body aches
• Joint pains
• Vomiting
• Diarrhea
• Rash
• Fatigue and weakness lasting for weeks or months

About 1 in 150 people who are infected develop a severe illness affecting the central nervous system, such as encephalitis (inflammation of the brain) or meningitis (inflammation of the membranes that surround the brain and spinal cord). Symptoms of severe illness include:

• High fever
• Headache
• Neck stiffness
• Stupor
• Disorientation
• Coma
• Tremors and/or convulsions
• Muscle weakness
• Vision loss
• Numbness and/or paralysis

For more information, see the CDC WNV Symptoms, Diagnosis, & Treatment web page.

WNV is diagnosed by a healthcare provider, who can order blood tests to look for evidence of WNV infection should you begin to experience the signs and symptoms listed above. 

For more information, see the CDC WNV Symptoms, Diagnosis, & Treatment webpage.

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

According to data from the past ten years, LACE cases are generally reported in the Eastern portion of the state.

In Tennessee, illness onset for cases of LACE is mainly reported in the warmer months of the year. The number of reported LACE cases is lowest in the winter and spring (December-April), slightly increases in the early- to mid-summer (May-July), peaks in August, and then gradually declines through autumn (September-November).

Signs and symptoms of LACE typically begin 3-10 days after being bitten by an infected mosquito. Late spring through mid summer is the time of year when Tennesseans are most at risk for contracting LACV from a mosquito.

Anyone who spends time outdoors in Tennessee is at risk of contracting LACV from the bite of an infected mosquito. However, the majority of people infected with LACV do not develop LACE. The severe neuroinvasive disease associated with LACE occurs most frequently in chlidren under the age of 16 years.

From 2013-2023, only one Tennesseean above the age of 19 developed LACE.

LACE is most often diagnosed for severe cases, because testing for this virus is rarely done on patients presenting with mild febrile illness. As a result, most LACE cases have already developed severe neuroinvasive disease by the time that they are diagnosed, leading to a high hospitalization rate.

Over the last 10 years in Tennessee, 96% of LACE cases were hospitalized for severe illness. Although LACE case numbers decreased in 2015 and 2021-2022, there has been a median of approximately 15 cases per year in our state.

Most people infected with LACV do not have any symptoms. For those who do develop symptoms, the time from infected mosquito bite to feeling sick ranges from 3-10 days. Early signs and symptoms are usually mild or moderate, and they may include:

• Fever (lasting for 2-3 days)
• Headache
• Nausea and/or vomiting
• Tiredness and reduced activity/alertness

Severe neuroinvasive disease classified as LACE occurs most frequently in children under the age of 16 years. Although seizures and other nervous system conditions are common, most patients recover completely. However, some effects on the central nervous system from severe LACE can persist overtime. Long-term effects can include:

• Recurrent seizures
• Partial paralysis of one side of the body
• Cognitive or behavioral impairments

For more information, see the CDC's LACE Symptoms, Diagnosis, & Treatment webpage.

LACE is diagnosed by a healthcare provider, who can order blood tests to look for evidence of LACV infection if you experience the symptoms described above. For more information, see the CDC's LACE Symptoms, Diagnosis, & Treatment web page.

For those EEE-infected persons who experience symptoms, the time from infected mosquito bite to feeling sick ranges from 4-10 days. The type of illness that develops depends on the age of the person and other factors, but in general, EEE infection can result in febrile illness or neurologic disease. Febrile illness lasts for 1-2 weeks, and most people recover completely. Signs and symptoms of febrile illness can include:

• Fever
• Chills
• Body aches
• Joint pain

Neurologic disease resulting from EEE infection can include meningitis (infection of the membranes that surround the brain and spinal cord) or encephalitis (infection of the brain). People who recover from this severe illness are often left with long-term physical or mental impairments, which can range from mild brain dysfunction to severe intellectual or social impairment. In addition to fever and headache, signs and symptoms of neurologic disease can include:

• Diarrhea
• Seizures
• Behavioral changes
• Drowsiness
• Coma

For more information, see the CDC's EEE Symptoms, Diagnosis, & Treatment webpage.

EEE is diagnosed by a healthcare provider, who can order blood tests to look for evidence of EEE virus infection if you experience the symptoms described above. For more information, see the CDC's EEE Symptoms, Diagnosis, & Treatment webpage.

The gradient on the map below refers to average SFR 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 were 4,352 probable and confirmed cases of SFR reported. The top ten counties with the highest reported SFR cases in 2022 and 2023 were in the Mid-Cumberland, South Central, Southeast, Upper Cumberland, and Western regions. Sumner, Lawrence, Stewart, and Wayne counties had an increase in cases in 2023, while case numbers in Davidson, Dickson, and Maury counties dropped by 50% or more. Overall, there was a noticeable decrease in SFR cases in 2023 as compared to 2022.

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

Peak transmission for SFR in Tennessee is associated with tick season, which occurs annually from early spring to late summer.

Anyone who spends time outdoors in Tennessee is at risk of contracting SFR, because the ticks that spread this disease are 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.

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 these ticks.

Individuals of any reported gender, sex, and age group in Tennessee can get sick with SFR. However, most cases of SFR are reported in residents 50 years of age or older. Additionally, within every age group, significantly more SFR cases affect male patients than female patients.

The number of SFR cases reported in Tennessee used to be over 600 annually; however, COVID-19 and a case definition change in 2020 likely reduced this number in 2020-2023. Despite this recent decline, SFR is still a highly reported tick-borne disease in Tennessee.

Early signs and symptoms of SFR typically mirror those of other tick-borne diseases, such as fever and headache. However, if left untreated, this disease can rapidly progress to a serious and life-threatening illness. Common signs and symptoms include:

• Fever
• Headache
• Rash (red splotches or pinpoint dots)
• Nausea
• Vomiting
• Stomach pain
• Muscle pain
• Lack of appetite

Some patients who recover from severe SFR may be left with permanent damage as a result of the acute illness. Long-term health problems can include:

• Amputation of arms, legs, fingers, or toes from damage to blood vessels in these areas
• Hearing loss
• Paralysis
• Mental disability

For more information, see the CDC Rocky Mountain Spotted Fever webpage.

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

For more information, see the CDC Rocky Mountain Spotted Fever webpage.

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

Davidson and Williamson counties accounted for 27% of all ehrlichiosis cases reported in the state in 2023.

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

Signs and symptoms of ehrlichiosis typically begin 5-14 days after being bitten by an infected lone star tick. Therefore, late spring through early summer (April-June) is the time of year when Tennesseans are most at risk for contracting ehrlichiosis.

Anyone who spends time outdoors in Tennessee is at risk of contracting ehrlichiosis, because the lone star ticks that spread this disease are 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.

Lone star 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 these ticks.

Individuals of any reported gender, sex, and age group in Tennessee can get sick with ehrlichiosis. However, most cases of ehrlichiosis are reported in older residents over 50. Additionally, within almost every age group, ehrlichiosis was reported more in males than females.

The number of ehrlichiosis cases reported in 2023 increased 22% from the previous year. Although 2020 saw a significant decrease in case counts, likely due to less human-tick exposure during the start of the COVID-19 pandemic, reports of ehrlichiosis in Tennessee have generally been rising since 2015.

Unlike other reportable tick-borne diseases in the state, ehrlichiosis results in hospitalization for 35-65% of Tennesseeans who become infected. In 2023, approximately 56% of all probable and confirmed ehrlichiosis cases were hospitalized for their illness.

Signs and symptoms of ehrlichiosis 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
• Confusion
• Rash that looks like red splotches or pinpoint dots (more common in children than adults)

If antibiotic treatment is delayed, ehrlichiosis can sometimes cause severe illness. Early treatment can reduce your risk of developing severe illness. Late stage signs and symptoms can include:

• Damage to the brain or nervous system (e.g. inflammation of the brain and surrounding tissue)
• Respiratory failure
• Uncontrolled bleeding
• Organ failure
• Death

For more information, see the CDC Signs and Symptoms of Ehrlichiosis webpage.

Ehrlichiosis is diagnosed by a healthcare provider, who can order blood tests to look for evidence of Ehrlichia chaffeensis or Ehrlichia ewingii 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 Ehrlichiosis Diagnosis and Testing webpage.

The gradient on the map below refers to average Lyme disease 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 were 382 Lyme disease cases reported; 94% of those cases were in residents from the Middle and Eastern grand divisions of the state. In the last decade, 9 of the top 15 counties with the highest incidence rate of Lyme are in the northeast region that borders Virginia and North Carolina. The other counties with the highest incidence rates tend to fall along the northern part of the state that borders Kentucky. This may indicate a need for enhanced surveillance and messaging to healthcare providers in these regions.

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

Signs and symptoms of Lyme disease typically begin 3-30 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 Lyme disease.

Anyone who spends time outdoors in Tennessee is at risk of contracting Lyme disease, because the black-legged tick that spreads this disease are 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 these ticks.

Individuals of any reported gender, sex, and age group in Tennessee can get sick with Lyme disease. However, a relatively larger number of cases of Lyme disease are reported in female-identifying patients ages 30-55.

The number of Lyme disease cases reported per year in Tennessee has been steadily increasing since 2014. In 2023, a 39 confirmed and probable cases were reported. The overall rise in the past 8 years can be attributed to the expansion of Ixodes ticks from the northeastern to the southeastern U.S. region.

Hospitalization rates for Lyme disease patients in Tennessee have been consistently low.

Signs and symptoms of Lyme disease typically develop between 3-30 days after being bitten by an infected tick. Early signs and symptoms may include:

• Fever, chills, headache, fatigue, muscle and joint aches, and swollen lymph nodes
• Erythema migrans (EM) rash:
  • Occurs in approximately 70-80% of infected persons
  • Begins at the site of a tick bite after a delay of 3-30 days (average is about 7 days)
  • Expands gradually over several days, reaching up to 12 inches or more across
  • May feel warm to the touch, but is rarely itchy or painful
  • Sometimes clears as it enlarges, resulting in a target or "bull's-eye" appearance
  • May appear on any area of the body
  • Does not always appear as a "classic" EM rash

If antibiotic treatment is delayed, Lyme disease can produce a wide array of symptoms, depending on the stage of infection. Late stage signs and symptoms occur days to months after a tick bite and can include:

• Severe headaches and neck stiffness
• Additional EM rashes on other areas of the body
• Facial palsy (loss of muscle tone or droop on one or both sides of the face)
• Arthritis with severe joint pain and swelling, particularly in the knees and other large joints
• Intermittent pain in tendons, muscles, joints, and bones
• Heart palpitations or an irregular heart beat
• Episodes of dizziness or shortness or breath
• Inflammation of the brain and spinal cord
• Nerve pain
• Shooting pains, numbness, or tingling in the hands or feet

For more information, see the CDC Signs and Symptoms of Untreated Lyme Disease webpage.

Lyme disease is diagnosed by a healthcare provider, who will use a combination of clinical observations and laboratory testing to assess whether Borrelia burgdorferi is present. Providers will consider the signs and symptoms of Lyme disease, the likelihood that the patient has been exposed to infected black-legged ticks, the possibility that other illnesses may cause similar symptoms, and the results of laboratory testing to decide whether a diagnosis should be made.

The laboratory criteria recommended by the CDC involves two tests, both of which can be done using the same blood sample. 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 Clinical Testing and Diagnosis for Lyme Disease webpage.

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.

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.

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.

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 Anaplasmosis webpage.

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 Anaplasmosis webpage.