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United States Department of Agriculture

Agricultural Research Service

Research Project: CONTROL, IMMUNOLOGY AND GENOMICS OF SPIROCHETE DISEASES Title: Asymptomatic and chronic carriage of Leptospira interrogans serovar Pomona in California sea lions (Zalophus californianus)

Authors
item Prager, K -
item Greig, Denise -
item Alt, David
item Galloway, Renee -
item Hornsby, Richard
item Palmer, Lauren -
item Soper, Jennifer -
item Wu, Qingzhong -
item Zuerner, Richard -
item Gulland, Frances -
item Lloyd-Smith, James -

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 25, 2013
Publication Date: February 4, 2013
Repository URL: http://handle.nal.usda.gov/10113/56489
Citation: Prager, K.C., Greig, D.J., Alt, D.P., Galloway, R.L., Hornsby, R.L., Palmer, L.J., Soper, J., Wu, Q., Zuerner, R.L., Gulland, F.M., Lloyd-Smith, J.O. 2013. Asymptomatic and chronic carriage of Leptospira interrogans serovar Pomona in California sea lions (Zalophus californianus). Veterinary Microbiology. 164(1-2):177-183.

Interpretive Summary: There are many different serovars of leptospiral bacteria which infect a variety of hosts. Traditional understanding of these infections divides affected host animals into either maintenance or accidental hosts. In maintenance hosts, limited clinical signs are observed. The maintenance host can serve as a chronic carrier, shedding leptospira over long periods and serving as a continued source of exposure to other animals and people. Accidental hosts can experience mild to severe disease but do not become chronically infected or contribute significantly to disease transmission and persistence. Since 1970, periodic outbreaks of leptospirosis have resulted in clinical disease and death of California sea lions (Zalophus californianus) along the Pacific coast of North America. Collected data suggest that Leptospira interrogans serovar Pomona is the infecting serovar and persists within the California sea lion population, although the mechanism of persistence is unknown. Blood and culture samples were obtained and evaluated from wild, free-ranging sea lions and from two sea lions in rehabilitation settings. Asymptomatic carriage was detected in samples from 10 wild, free-ranging sea lions and chronic asymptomatic carriage was demonstrated for at least 9 weeks in the two rehabilitating sea lions. These results provide a potential mechanism for persistent circulation of leptospirosis in the California sea lion population. Because sea lions suffer significant disease and mortality from this strain of Leptospira, the results indicating both chronic and asymptomatic carriage serve to expand the traditional view of Leptospira epidemiology and enhance the scientific study of leptospiral infection.

Technical Abstract: Since 1970, periodic outbreaks of leptospirosis, caused by pathogenic spirochetes in the genus Leptospira, have caused morbidity and mortality of California sea lions (Zalophus californianus) along the Pacific coast of North America. Yearly seasonal epizootics of varying magnitude occur between the months of July and December, with major epizootics occurring every 3-5 years. Genetic and serological data suggest that L. interrogans serovar Pomona is the infecting serovar and is enzootic in the California sea lion population, although the mechanism of persistence is unknown. We report asymptomatic carriage in 10 wild, free-ranging sea lions and chronic asymptomatic carriage for at least 9 weeks in two sea lions in rehabilitation settings. Because sea lions suffer significant disease and mortality from this strain of Leptospira, existence of chronic carriage would contribute to a growing body of literature challenging the traditional view of Leptospira epidemiology. This view holds that, for a given serovar, host species are divided into distinct categories of maintenance and accidental hosts, with dramatically different traits. In maintenance host species, individuals become chronic carriers without significant disease and the pathogen persists enzootically. In accidental host species, the same serovar leads to acute infections that range from subclinical to fatal, but individuals do not become chronic carriers or contribute significantly to ongoing transmission and the pathogen does not circulate persistently. Our findings of chronic carriers provide a potential mechanism for persistent circulation of Leptospira in the California sea lion population, particularly if these animals shed infectious leptospires for months to years.

Last Modified: 8/29/2014
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