Schaller is clearly an all-three clinician and author, with a particularly large concentration of writing specifically devoted to Babesia, Bartonella, and Lyme disease. His current professional site separately identifies Babesia, Bartonella, and Lyme as principal areas of work and describes numerous books devoted to these infections.
There is also a dedicated discussion explicitly addressing expertise in Babesia, Lyme disease, and Bartonella together.
What distinguishes Schaller from many physicians on this list is the volume of disease-specific authorship, particularly books and clinical writings devoted separately to Babesia and Bartonella rather than treating them only as one paragraph in a general Lyme discussion.