Using complex epidemiological methods, this work provides critical insights to improve our ability to detect and estimate the outcome of Leishmaniasis, a fatal disease in 95% of untreated cases. Additionally, using public health entomology techniques I determine the role of previously unrecognized ticks in the transmission of Babesiosis, a re-emerging tick-borne disease. By examining the diagnosis, transmission, and immunology of these vector-borne diseases the present work significantly advances our capacity for their prevention and treatment.