We reviewed scientific literature pertaining to known and putative disease 
agents associated with the lone star tick, Amblyomma americanum. Reports in the 
literature concerning the role of the lone star tick in the transmission of 
pathogens of human and animal diseases have sometimes been unclear and even 
contradictory. This overview has indicated that A. americanum is involved in the 
ecology of several disease agents of humans and other animals, and the role of 
this tick as a vector of these diseases ranges from incidental to significant. 
Probably the clearest relationship is that of Ehrlichia chaffeensis and A. 
americanum. Also, there is a definite association between A. americanum and 
tularemia, as well as between the lone star tick and Theileria cervi to 
white-tailed deer. Evidence of Babesia cervi (= odocoilei) being transmitted to 
deer by A. americanum is largely circumstantial at this time. The role of A. 
americanum in cases of southern tick-associated rash illness (STARI) is 
currently a subject of intensive investigations with important implications. The 
lone star tick has been historically reported to be a vector of Rocky Mountain 
spotted fever rickettsiae, but current opinions are to the contrary. Evidence 
incriminated A. americanum as the vector of Bullis fever in the 1940s, but the 
disease apparently has disappeared. Q fever virus has been found in unfed A. 
americanum, but the vector potential, if any, is poorly understood at this time. 
Typhus fever and toxoplasmosis have been studied in the lone star tick, and 
several non-pathogenic organisms have been recovered. Implications of these 
tick-disease relationships are discussed.