Its definitely a tick borne issue but there is also a ton of evidence supporting transmission through dog fights. That is why it is in the greyhound and APBT population. They are not necessarily more susceptible, just more likely to be put in a position to contract it from dog bites.
It is more prevalent in the southern states in the tick populations.
There are TONS of tick illnesses that are deadly. Unfortunately there is only one dog in my house that doesnt have at least one tick disease