Environmental persistence and control of the nasopulmonary mite Halarachne halichoeri: Implications for sea otter rehabilitation.

Nasopulmonary mite infestations are increasingly recognized as a potential contributor to respiratory disease and secondary infections in southern sea otters (Enhydra lutris nereis), yet the environmental persistence and control of these parasites remain poorly understood. We conducted controlled in vitro time-to-event survival experiments to evaluate the persistence of larval Halarachne halichoeri under varying environmental conditions and the efficacy of disinfectants and alternative treatments relevant to marine mammal rehabilitation facilities. We also evaluated the in vitro acaricidal efficacy of ivermectin, a common host-directed treatment. Larval mites exhibited prolonged survival under moist conditions, persisting for up to 54 days in 25 ‰ salinity and up to 25 days in 35 ‰ salinity, representing rehabilitation and natural marine seawater, respectively. In contrast, desiccation markedly reduced survival, with no individuals surviving beyond 10 days. Standard disinfectants, including bleach (0.8%), Virkon-S™ (1%), and accelerated hydrogen peroxide (Rescue™ 1:64), did not produce rapid mortality at typical contact times, indicating limited acaricidal efficacy. Among alternative treatments tested, only permethrin (1:100) resulted in rapid and consistent mortality. Ivermectin significantly reduced median survival from 192 h in controls to 4 h but did not eliminate all mites. These findings demonstrate that larvae can persist in moist environmental reservoirs long enough to enable indirect transmission, particularly under reduced salinity conditions. The limited effectiveness of standard disinfectants highlights a critical gap between microbial biosecurity practices and parasite control. This is especially relevant in captive care and rehabilitation facilities, where mites may spread directly between otters or indirectly through mite-contaminated enclosures and fomites. Environmental persistence, host aggregation, and incomplete treatment may contribute to recurrent and widespread infestations. Effective mite control will require integrated host-directed treatment and environmental mitigation. Improving understanding of parasite ecology in natural and managed systems is essential for minimizing infestation risk and associated pathology and supporting conservation for this threatened species.