Leptospirosis and the California Sea Lions
by Lauren Sorich

Sea Lions picture by John Wilsher
Photo from The Leptospirosis Information Center
Photo from The Leptospirosis Information Center
Photo from oregonstate.edu/.../2007/Jan07/lepto.html
Photo from oregonstate.edu/.../2007/Jan07/lepto.html

Abstract: The purpose of this site is to educate people on the effects that leptospirosis has on the California sea lion and humans. Topics that will be discussed are structure of the pathogen that causes the disease, how the sea lions get the disease, how it is passed from sea lion to sea lion, how it is transmitted from sea lions to other animals, how it affects humans, and treatment in humans. The most common cause for all cases is coming in contact with Leptospira-contaminated water or soil.

Over the past ten years, thousands of marine animals have died unexpectedly and veterinary microbiologists are trying to find the cause for each outbreak. In 2004, leptospirosis was the cause of death for 30 California sea lions. These, along with other marine mammal deaths, raise awareness that entire populations of marine mammals may be destroyed. Until recently veterinary microbiology has been a neglected field of study partly because gathering samples from animals that live in the open ocean and performing bacterial analysis on them is difficult. Veterinary microbiologists hope that the increased study in this field will promote wildlife management and also provide models for studing human diseases (Tortora et al., 2007).
Leptospirosis is one of the most widespread bacterial diseases that can be transmitted from animals to humans and affects most mammalian species. It is well documented and characterized in terrestrial species, however, less is known regarding the distribution and impact of leptospirosis in marine mammals. Leptospirosis can develop into either a chronic infection with low mortality or into a potentially lethal infection (Faine et al., 1999).

This research was of interest to me because animals are affected by the disease around the area that I live in and I wanted to know more about it so that I can avoid contact with the disease. I also care for the animals with this pathogen and would hate to see species destroyed.

Structure- The spirochete Leptospira interrogans is what causes leptospirosis. Leptospira has a spiral shape that’s only about 0.1µm in diameter and is wound so tight that it is barely visible under a dark field microscope. It does not stain easily and is difficult to see under a normal light microscope. L. interrogens gets its name because the ends are hooked like a question mark. It is an obligate aerobe that can grow in a variety of artificial media supplemented with rabbit serum (Tortora et al., 2007).

How sea lions get it- One possible way sea lions contract this disease is exposure to Leptospira-contaminated urine while on shore or while swimming in fresh water estuaries (Zuerner et al., 2009). The male sea lions spend between 20-55% of their time resting on shore, which allows exposure to terrestrial mammals that may be infected with the pathogen (Weise et al., 2006). Leptospira can’t tolerate salt, which suggests that infection most likely occurs through close contact with infected animals on the shore (Zuerner et al., 2009).

How it’s spread to other sea lions- California sea lions (Zalophus californianus) breed in rookeries along the southern California coast during May and June (Zuerner et al., 2009). The female sea lions typically stay close to the rookeries to nurse their pups, but they may move as far north as Monterey Bay, however the males travel north and spend the winter anywhere from California to south Alaska (Melin, 2002). Even though they stay close to the coast, occasionally they leave to look for food, and males can cover 644 km on a single trip (Weise et al., 2006). Their ability to travel great distances gives the disease the opportunity to spread geographically (Zuerner et al., 2009).

How it’s spread to other animals- Terrestrial animals may get leptospirosis because sick or injured sea lions either die at sea or are stranded on beaches where other animals can come into contact with them. Leptospirosis has a latency period of about 10-14 days between contact and developing symptoms, leading researchers to believe that the animals are able to travel during this latency period spreading the disease. Since some of the population is continuously in a latency state of infection, the distribution of infected animals spreads as animals disperse across different geographical areas. Infected animals are often found near fresh water estuaries which potentially increases the chance of transmitting the disease to humans, domesticated animals, and terrestrial wildlife (Zuerner et al., 2009).

How it affects humans- Animals that are infected with L. interrrogans can shed the bacteria in their urine for extended periods of time (Tortora et al., 2007). Humans can become infected by coming in contact with water or soil that is contaminated with urine or by coming in contact with animal tissue that is infected (Faine, 1982). People who are most at risk are those whose work exposes them to animals or animal products. Typically, the pathogen infects a host by entering through minor abrasions in the skin or mucous membranes. If it is ingested, it enters the body through the mucosa of the upper digestive system. Cats and dogs are the most common sources in the US. Even when immunized, domestic dogs may continue to shed leptospira because they have a sizeable rate of infection. Once infected, headaches, muscular aches, chills, and fever occur after an incubation period of 1-2 weeks. Days later these symptoms disappear, however, a few days after that, a second episode of fever may occur. The kidneys and liver may become infected, this is known as Weil’s disease and kidney failure is the most common cause of death (Tortora et al., 2007). Weil’s syndrome is characterized by jaundice, hemorrhage and severe renal failure (Liu et al., 2007). About 50 cases are reported each year in the US, but because the symptoms are not distinctive many cases are probably never diagnosed (Tortora et al., 2007).

Diagnosis/treatment in humans-: Most cases of leptospirosis are diagnosed by a serological test that is complicated and usually done by central reference laboratories. However, a diagnosis can also be made by sampling blood, urine, or other fluids for the organism or its DNA, and Doxycycline is the recommended antibiotic for treatment (Tortora et al., 2007).

Literature Cited:
Faine, S., Adler, B., Bolin, C., Perolat, P. (1999). Leptospira and Leptospirosis second ed. MediSci, Melbourne, Australia.

Melin, S.R., (2002). The Foraging Ecology and Reproduction of the California
sea lion (Zalophus californianus californianus). University of Minnesota,

Liu, Yunying, Zheng, Wei, Li Liwei, Mao, Yafei, and Yan, Jie. (2007). Pathogensis of leptospirosis: interaction of Leptospira interrogans with in vitro cultured mammalian cells. Med Microbiol Immunol 196: 233-239.

Tortora, Gerard J., Funke, Berdell R., and Case, Christine L. (2007). Microbiology an introduction; ninth edition. San Francisco, CA Pearson Education Inc.

Weise, M.J., Costa, D.P., Kudela, R.M., (2006). Movement and diving behavior of male California sea lion (Zalophus califorianus) during anomalous oceanographic conditions of 2005 compared to those of 2004. Geophys. Res. Lett. 33, L22S10.

Zuerner, Richard L., Cameron, Caroline E., Raverty, Stephen, Robinson, John, Colegrove, Kathleen M., Norman, Stephanie A., Lambourn, Dyanna, Jeffries, Steven, Alt, David P., and Gulland, Frances. (2009). Geographical dissemination of Leptospirosa interrogans serovar Pomona during seasonal migration of California sea lions. Veterinary Microbiology 137 105–110.