Tick species established in Massachusetts, 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. | 59,509 | 14 | 23 |
| 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. | 3,471 | 14 | 2 |
| Anaplasmosis Anaplasmosis is a bacterial infection (Anaplasma phagocytophilum) spread by black-legged ticks across the Northeast, Upper Midwest, and Pacific Coast. | 2,960 | 14 | 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. | 47 | 14 | 2 |
| Tularemia Tularemia is a highly infectious bacterial disease (Francisella tularensis) transmitted by tick bites, deer fly bites, and contact with infected animals. | 41 | 14 | 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. | 31 | 14 | 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. | 6 | 14 | 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 | 14 | 2 |
| Rank | County | Total cases | Diseases | Latest year |
|---|---|---|---|---|
| 01 | Middlesex County | 11,385 | 8 | 2023 |
| 02 | Plymouth County | 9,122 | 8 | 2023 |
| 03 | Worcester County | 7,771 | 8 | 2023 |
| 04 | Bristol County | 7,681 | 8 | 2023 |
| 05 | Norfolk County | 6,849 | 8 | 2023 |
| 06 | Essex County | 5,818 | 8 | 2023 |
| 07 | Barnstable County | 4,788 | 8 | 2023 |
| 08 | Berkshire County | 2,812 | 8 | 2023 |
| 09 | Hampden County | 2,689 | 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.