TABLE 1.

R. rickettsii strain history of isolates used in this study

Strain	Isolate location	Year	Source	Passage historya
Sheila Smith	Missoula, MT	1946	Human	5 YS, 4 V, 1 B, 10 V
Morgan	Kannapolis, NC	1975	Human	4 YS, 7 V, 1 B, 14 V
Sao Paulo	Sao Paulo, Brazil	1933	Amblyomma cajennense	8 YS, 4 V, 1 B, 5 V
R	Bitterroot Valley, MT	1949	Dermacentor andersoni	10 YS, 3 V, 1B, 12 V
HLP7421	Bitterroot Valley, MT	1961	Haemaphysalis leporispalustris	7 YS, 6 V, 1 B, 5 V
Iowa	Iowa	1938	Dermacentor variabilis	271 YS, 1 GP, 9 V, 1 B, 13 V

^aNumber of passages in yolk sac (YS), Vero cells (V), guinea pig (GP), and BALB/c mouse (B).