The epidemiological role of the crab-eating fox Cerdocyon thous in the transmission of Leishmania infantum is assessed in a longitudinal study in Amazon Brazil. A total of 37 wild-caught foxes were immunologically and clinically monitored, and 26 foxes exposed to laboratory colonies of the sandfly vector Lutzomyia longipalpis, over a 15-month period. In total 78% (29/37) of foxes were seropositive for anti-Leishmania IgG on at least 1 occasion, and 38% (8/37) had infections confirmed by PCR and/or by culture. Point prevalences were 74% (serology), 15% (PCR), and 26% (culture). No signs of progressive disease were observed. None of the foxes were infectious to the 1469 sandflies dissected from 44 feeds. A conservative estimate of the possible contribution of foxes to transmission was 9% compared to 91% by sympatric domestic dogs. These results show that crab-eating fox populations do not maintain a transmission cycle independently of domestic dogs. The implication is that they are unlikely to introduce the parasite into Leishmania-free dog populations.