Parasites are endangered by the conservation of their hosts: Meta-analyses of the effect of host captivity on the odds of parasite infection

Parasites are important drivers of ecosystem functions and play a key role in the maintenance of ecosystem health. However, parasites may be threatened by host conservation, as well as by host extinction. Captive management is of increasing importance for conserving threatened host species, but captivity represents a drastic environmental change that may in turn threaten parasites. To address this concern, we examined how host captivity affects the odds of parasite infection and identified which parasite life-history traits (particularly modes of transmission) are the  strongest predictors of parasite decline. Data were collated from 45 studies examining parasite prevalence in both captive and free-range host  populations across a total of 55 host and 158 parasite species. We performed meta-analyses of these studies and found that overall, the odds of infection by parasites were not different between host populations in captive and free-range environments. However, the odds of infection by helminths were lower in captivity. Parasites with indirect life cycles, especially helminths with complex life cycles and vector-borne protozoa, also had lower odds of infecting hosts in captivity. Finally, parasites transmitted through the environment with direct life cycles, particularly  environmentally-transmitted helminths, had lower odds of infecting hosts in captivity. Parasite losses in captivity are likely caused by the use of antiparasitic drugs, and the biotic and abiotic differences between captive and free-range environments. If the goals of activities such as captive breeding are to re-establish self-sustaining ecosystems, then conservation efforts need to include both hosts and their parasites in captive management programs.