AbstractTolerance to infection should be selected when exposure is highly probable, when parasite virulence is relatively low and when the costs of resistance outweigh those of damage control. This strategy may be particularly favoured in slow-pace-of-life species that prioritize survival over short-term reproduction. Here, we investigate infection by Anaplasma amazonensis, a recently described tick-borne bacterium from the Amazon basin, in two sloth species: the pale-throated sloth (Bradypus tridactylus) and Linnaeus’s two-toed sloth (Choloepus didactylus), emblematic slow-pace-of-life species. Our screening of 175 wild individuals revealed a single A. amazonensis strain infecting both species, with high prevalence (48–63%) and evidence of sustained circulation for at least 25 years. Clinical assessments further indicated that infections were largely asymptomatic, with no significant effects on body condition, scaled mass index or reproduction, although rare instances of reduced haematocrit suggest transient erythrocyte loss during acute phases. The high prevalence of infection in apparently healthy wild sloths supports the hypothesis of a tolerance mechanism that mitigates overt clinical symptoms and favours the circulation of A. amazonensis.
Duron et al. (Wed,) studied this question.