Toxoplasma gondii infections are associated with boldness towards lions in wild hyena hosts

is widely reported to manipulate the behavior of its non-definitive hosts in ways that promote lethal interactions with the parasite’s definitive feline hosts. Nonetheless, there is a lack of data on the association between infection and costly behavioral interactions with felids in nature. Here, we report that three decades of field observations reveal infected hyena cubs approach lions more closely than uninfected peers and have higher rates of lion mortality. Our findings support the hypothesis that manipulation of host boldness is an extended phenotype that promotes parasite transmission from intermediate hosts to feline predators. While upregulating hyena boldness toward lions might achieve this, it may also reflect a collateral influence of manipulative traits that evolved in other hosts (e.g., rodents). In either case, our findings corroborate the potential impacts of a globally distributed and generalist parasite () on fitness-related interaction with felids in a wild host.