These datasets (S2-S3) document the transmission of a bacterial pathogen (Mycoplasma agassizii) between desert tortoises (Gopherus agassizii) experimentally introduced in captivity and were used to create and compare models predicting transmission probability given data on the hosts and their interactions. Dataset S2 includes variables describing the individual tortoises interacting, e.g. id, sex; variables describing the length of their interaction, e.g., number of days cohabitating, hours of direct contact; and variables estimating the infection level (based on data in S3) of infected tortoises involved in the interaction with the focal host. Interaction time and the amount of bacteria present in an infected host were used to calculate “dose” variables that represent the intensity of exposure to the pathogen. These data were used to estimate model parameters for multiple generalized linear models (glm) with predictor variables related to exposure time to an infected host and host characteristics. The response variable or event of interest was the infection status of the exposed tortoise after a period of interaction. Infection status was defined in two ways (described in section 15) and determined using qPCR of tissue samples collected at intervals – the results of which are presented in the S3 dataset. The analyses allowed us to identify interactions that have high transmission likelihood, and so we explored the contact patterns of a wild tortoise population (25 individuals with overlapping or contiguous homeranges) to estimate how frequently high-risk contacts occur (Dataset S4). This dataset includes all interactions (tortoise ids of interacting pair, date & time interaction began, and interaction duration) documented between tortoises fitted with proximity logging devices. Each device detects other devices when tortoises are approximately 10 cm apart and ends an interaction when tortoises have remained further than 10 cm for 1 minute. These data are associated with the following publication: Aiello, C. M., Nussear, K. E., Esque, T. C., Emblidge, P. G., Sah, P., Bansal, S. and Hudson, P. J. (2016), Host contact and shedding patterns clarify variation in pathogen exposure and transmission in threatened tortoise Gopherus agassizii: implications for disease modelling and management. J Anim Ecol, 85: 829–842. doi:10.1111/1365-2656.12511