Abstract

Minimal information is available regarding the distribution and impact of leptospirosis in marine mammals; however, infections have been documented in pinnipeds including California sea lions (Zalophus californianus), Northern fur seals (Callorhinus ursinus), Pacific harbor seals (Phoca vitulina richardsii), and Steller sea lions (Eumetopias jubatus).^1-5 Although clinical disease and pathology have not been demonstrated in manatees, this presentation provides an overview of past, present, and ongoing research documenting the seroprevalence of Leptospira in West Indian manatees (Trichechus manatus) from Florida, Belize, and Puerto Rico.

As part of a broad serological survey of Leptospira interrogans in free-ranging, rescued, and captive Florida manatees (Trichechus manatus latirostris), 142 serum samples collected and archived between 1979 and 1996 were tested for 13 serovars using microscopic agglutination test (MAT). Positive antibody titers (> 1:100) to one or more serovars were identified in 25% of the samples. Positive results were most commonly obtained for serovars bratislava and autumnalis in this study. The highest titers were against serovars L. australis (≥ 1:6400), L. bratislava (≥ 1:3200), and L. canicola (≥ 1:1600). Seropositive results identified a significant relationship between age classes and between geographical locations, but the difference between males and females was not significant.

A similar serological survey was performed for 6 Leptospira interrogans serovars on serum samples collected and archived between 1997 and 2009 from 112 free-ranging manatees captured in Belize. Positive antibody titers (> 1:100) to one or more serovars were identified in 23% of the manatees. Positive titers were most commonly obtained for serovars L. bratislava and the highest titer was against L. canicola (> 1:1600); however, serovars australis and autumnalis were not tested in this study. A significant difference was identified between geographical location of capture and seropositivity; however, no significant relationship between sex or age class and seropositivity was identified in this study.

Currently, serum samples from free-ranging and captive manatees in Florida and Puerto Rico are tested in efforts to provide a wider geographic distribution to the previous surveys. Titers obtained from four free-ranging manatees in Puerto Rico were negative for all tested serovars. Interestingly, two of five captive manatees maintained at Homosassa Springs Wildlife State Park in Florida tested positive with a titer > 1:100 for one or more serovars. One of these animals actually maintained a consistent titer (>1:1600) against serovar L. canicola for three years until it doubled (> 1:3200) without any apparent clinical signs of disease. Polymerase chain reaction (PCR) and culture of the urine for this specific animal was negative.

Clinical disease and pathology associated with Leptospira interrogans has not been identified in the West Indian manatee; therefore, further research is needed to learn more about the significance and interpretation of these positive antibody titers. Until potential consequences of this disease are identified or defined in manatees, surveillance should continue because it may have implications for population management, rehabilitation, and a better understanding of host - infectious agent interaction in Florida waters.

Acknowledgments

The aforementioned studies encompass many years of research and a large collaboration between numerous facilities. The authors wish to acknowledge the National Aquarium-Baltimore, SeaWorld in Florida, the Florida Department of Environmental Protection, Homosassa Springs Wildlife State Park, United States Geological Survey Sirenia Project, United States Fish and Wildlife Service, Florida Fish and Wildlife Conservation Commission, Marine Mammal Pathobiology Laboratory, University of Maryland, University of Florida Aquatic Animal Health Program, and the Bernice Barbour Foundation for their involvement and support. The authors specifically thank James Valade, Donna Szemer, Mark Sweat, Justin Krebs, Alex Bortolloto, Erika Hercher, Susan Lowe, and Dr. Mark Lowe. The authors also thank Drs. James Pearson and Beverly Schmitt for arranging laboratory testing at the National Veterinary Services Laboratory in Iowa and Michelle Davidson for arranging laboratory testing at the California Animal Health and Food Safety Laboratory System.

References

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