Results for use of the Rt-18R sandwich assay conducted in dog tick homogenate (5 medium-sized ticks ground into 10 ml of PBS) and then spiked with a 10^-2 (~ 1,000 cells/ml) or 10^-3 (~ 100 cells/ml) dilutions of R. typhi whole cells versus a zero blank. Data points represent the means and standard deviations of 3 readings.