Tick species established in Maryland, CDC-reported disease cases by county, and the county-level breakdown of where ticks and pathogens concentrate.
| Disease | Total cases | Counties | Years covered |
|---|---|---|---|
| Lyme disease Lyme disease is a bacterial infection (Borrelia burgdorferi) spread by black-legged ticks and the most common tick-borne illness in the US. | 33,787 | 24 | 23 |
| Spotted fever rickettsiosis Spotted fever rickettsiosis is a group of bacterial infections — Rocky Mountain spotted fever among them — spread by dog and wood ticks across the US. | 492 | 24 | 2 |
| Ehrlichia chaffeensis ehrlichiosis Ehrlichia chaffeensis ehrlichiosis is a bacterial infection of white blood cells spread by lone star ticks across the Southeast and south-central US. | 480 | 24 | 2 |
| Anaplasmosis Anaplasmosis is a bacterial infection (Anaplasma phagocytophilum) spread by black-legged ticks across the Northeast, Upper Midwest, and Pacific Coast. | 105 | 24 | 2 |
| Babesiosis Babesiosis is a malaria-like parasitic infection of red blood cells (Babesia microti) carried by black-legged ticks in the Northeast and Upper Midwest. | 41 | 24 | 2 |
| Ehrlichia ewingii ehrlichiosis Ehrlichia ewingii ehrlichiosis is a bacterial infection spread by lone star ticks, typically affecting immunocompromised patients in the southeastern US. | 6 | 24 | 2 |
| Tularemia Tularemia is a highly infectious bacterial disease (Francisella tularensis) transmitted by tick bites, deer fly bites, and contact with infected animals. | 6 | 24 | 2 |
| Undetermined ehrlichiosis/anaplasmosis Undetermined ehrlichiosis/anaplasmosis is the CDC reporting category for cases where the specific Ehrlichia or Anaplasma species could not be identified. | 5 | 24 | 2 |
| Rank | County | Total cases | Diseases | Latest year |
|---|---|---|---|---|
| 01 | Montgomery County | 4,148 | 8 | 2023 |
| 02 | Baltimore County | 3,723 | 8 | 2023 |
| 03 | Howard County | 3,544 | 8 | 2023 |
| 04 | Anne Arundel County | 2,980 | 8 | 2023 |
| 05 | Carroll County | 2,783 | 8 | 2023 |
| 06 | Frederick County | 2,641 | 8 | 2023 |
| 07 | Harford County | 2,612 | 8 | 2023 |
We frame this as epidemiology, not stigma — high-load counties are places with higher tick density and reporting completeness, not worse places to live.