Disciplines such as business and economics often rely on the assumption of rationality when explaining complex human behaviours. However, growing evidence suggests that behaviour may concurrently be influenced by infectious microorganisms. The protozoan infects an estimated 2 billion people worldwide and has been linked to behavioural alterations in humans and other vertebrates. Here we integrate primary data from college students and business professionals with national-level information on cultural attitudes towards business to test the hypothesis that infection influences individual- as well as societal-scale entrepreneurship activities. Using a saliva-based assay, we found that students ( = 1495) who tested IgG positive for exposure were 1.4× more likely to major in business and 1.7× more likely to have an emphasis in 'management and entrepreneurship' over other business-related emphases. Among professionals attending entrepreneurship events, -positive individuals were 1.8× more likely to have started their own business compared with other attendees ( = 197). Finally, after synthesizing and combining country-level databases on infection from the past 25 years with the Global Entrepreneurship Monitor of entrepreneurial activity, we found that infection prevalence was a consistent, positive predictor of entrepreneurial activity and intentions at the national scale, regardless of whether previously identified economic covariates were included. Nations with higher infection also had a lower fraction of respondents citing 'fear of failure' in inhibiting new business ventures. While correlational, these results highlight the linkage between parasitic infection and complex human behaviours, including those relevant to business, entrepreneurship and economic productivity.