Leptospira interrogans in the Galapagos sea lions (Zalophus wollebaeki).

Background: Leptospira are endemic and cause disease among California sea lions (Zalophus californianus), but the epidemiology of Leptospira in Galapagos sea lions (Z. wollebaeki) is almost completely unknown. Understanding the presence and circulation of this zoonotic pathogen is essential not only for the conservation of Galapagos sea lions, but also for assessing potential health risks to humans and other animals within the Galapagos archipelago. This study fills knowledge gaps by investigating Leptospira in this endemic host species to provide valuable insights into the dynamics of the pathogen in an isolated island ecosystem that is completely different from others in which Leptospira have been documented.

Results: In 2016, serological analyses detected 24 positive samples in the "El Malecón" rookery (n = 43) and 18 positive samples in the "Punta Pitt" rookery (n = 33), confirming exposure to pathogenic Leptospira species. In 2017, we identified 15 (n = 29) and 13 (n = 30) positive samples, respectively. Molecular analyses further detected leptospiral DNA in 70.8% (n = 24) of sand with urine samples and 45.8% (n = 24) of kidney samples. Amplicon sequencing of the secY gene fragment yielded 10 consensus sequences, confirming the circulation of Leptospira interrogans among Galapagos sea lions.

Conclusions: Our findings confirm that Galapagos sea lions are exposed to pathogenic Leptospira species and, for the first time, identify L. interrogans as the circulating species over two consecutive years. By expanding sampling across multiple rookeries, we provide a clearer picture of pathogen exposure in this endemic population. These results improve our understanding of Leptospira dynamics in marine mammals on remote islands, where management efforts aim to reduce disease risks from human activity, livestock, and synanthropic species.