Both a 53-year-old farmer and his 21-yearold son present in August with fever, myalgia, and malaise, which they came down with within a few hours of each other. The son had been home in southern Minnesota for only 3 weeks to help field train two new hunting dogs. You ask about potential tick bites, and the son did have one on him, which was quite engorged. Platelets and granulocytes are low in each man's blood. You ask one of your experienced techs to do a Giemsa stain on a thick blood smear. He calls, reporting clusters of cells resembling raspberries in granulocytes, even though nothing grows in any of the blood cultures. You realize that the blood cultures you set up will not grow and that you have two patients who have infections with a tick-borne obligate intracellular parasite of granulocytes. What genus does the organism belong to?