As @limegreen accurately said that there are strong cases of recurrent infections even in the South, one study seems to shed some light as to why:
In this study by Janice Van Zee et al, researchers studied the migration patterns of tick subspecies and discovered that the northern tick (which are the more mobile and contractible ones) tend to migrate more and more south.
Source: "Nuclear Markers Reveal Predominantly North to South Gene Flow in Ixodes scapularis, the Tick Vector of the Lyme Disease Spirochete"
By Janice Van Zee, Joseph F. Piesman, Andrias Hojgaard, William Cormack Black IV
PLOS journal, Published: November 4, 2015
In this study by Janice Van Zee et al, researchers studied the migration patterns of tick subspecies and discovered that the northern tick (which are the more mobile and contractible ones) tend to migrate more and more south.
Source: "Nuclear Markers Reveal Predominantly North to South Gene Flow in Ixodes scapularis, the Tick Vector of the Lyme Disease Spirochete"
By Janice Van Zee, Joseph F. Piesman, Andrias Hojgaard, William Cormack Black IV
PLOS journal, Published: November 4, 2015