Tick species established in Pennsylvania, 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. | 147,886 | 67 | 23 |
| Anaplasmosis Anaplasmosis is a bacterial infection (Anaplasma phagocytophilum) spread by black-legged ticks across the Northeast, Upper Midwest, and Pacific Coast. | 2,142 | 67 | 2 |
| 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. | 147 | 67 | 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. | 119 | 67 | 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. | 63 | 67 | 2 |
| Tularemia Tularemia is a highly infectious bacterial disease (Francisella tularensis) transmitted by tick bites, deer fly bites, and contact with infected animals. | 11 | 67 | 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. | 0 | 67 | 2 |
| Ehrlichia ewingii ehrlichiosis Ehrlichia ewingii ehrlichiosis is a bacterial infection spread by lone star ticks, typically affecting immunocompromised patients in the southeastern US. | 0 | 67 | 2 |
| Rank | County | Total cases | Diseases | Latest year |
|---|---|---|---|---|
| 01 | Chester County | 14,112 | 8 | 2023 |
| 02 | Bucks County | 10,822 | 8 | 2023 |
| 03 | Montgomery County | 10,457 | 8 | 2023 |
| 04 | York County | 7,342 | 8 | 2023 |
| 05 | Butler County | 5,580 | 8 | 2023 |
| 06 | Berks County | 5,521 | 8 | 2023 |
| 07 | Allegheny County | 4,723 | 8 | 2023 |
| 08 | Lancaster County | 4,688 | 8 | 2023 |
| 09 | Delaware County | 4,552 | 8 | 2023 |
| 10 | Westmoreland County | 4,536 | 8 | 2023 |
| 11 | Philadelphia County | 4,024 | 8 | 2023 |
| 12 | Clearfield County | 3,784 | 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.