Abstract
Between August and November 2001, a California sea lion (Zalophus californianus) and a gray seal (Halichoerus grypus) at the New York Aquarium developed nonspecific clinical signs (anorexia, depression, and lethargy). In combination with hematologic and biochemical changes (azotemia, icterus, immature white blood cells, and elevations of bilirubin, bile acids, hepatic enzymes, erythrocyte sedimentation rate, total protein, globulins, and fibrinogen), the illnesses were consistent with acute Leptospira interrogans infections. They recovered after treatment with antibiotics and supportive care. Serum samples were tested by microscopic agglutination at the Animal Health Diagnostic Laboratory for serologic evidence of exposure to 18 serovars of L. interrogans (L. interrogans serovars pomona, hardjo, grippotyphosa, icterohaemorrhagiae/copenhagenai, canicola, australis, autumnalis, ballum, bataviae, bratislava, icterohaemorrhagiae/icterohaemorrhagiae, javanica, pyrogenes, saxkoebing, sejroe, szwajizak, tarassovi, and wolffi). Active infection with L. interrogans serovar ballum was confirmed in each case by a greater than fourfold titer change to this serovar during the clinical course. The California sea lion's titer increased from 1:200 on 8 August to 1:1600 on 28 August. The grey seal's titer decreased from 1:6400 on 23 October to 1:800 on 14 November.
Following the diagnosis of L. interrogans serovar ballum, we performed a serosurvey of other aquarium pinnipeds and sea otters on samples obtained between May 2001 and February 2002. Asymptomatic L. interrogans serovar ballum infections were documented in three California sea otters (Enhydra lutris) and a harbor seal (Phoca vitulina) by either seroconversion or a fourfold or greater change in titer to this serovar. Three California sea lions had stable low positive titers (1:200-1:400), indicating prior exposure to this serovar. During this same interval, four Pacific walrus (Odobenus rosmarus divergens) remained seronegative for L. interrogans serovar ballum. Serologic results on samples from eight Northern fur seals (Callorhinus ursinus) obtained between 27 August and 7 November 2002 were also negative for this serovar. Clinically ill, asymptomatically infected, contact pinnipeds and sea otters were treated with doxycycline (5-10 mg/kg PO BID for 14 days) to minimize the risk of becoming chronic Leptospira carriers.
Infection with L. interrogans serovar pomona is well described in free-ranging California sea lions and Northern fur seals.1,3,4 This serovar, as well as others that commonly affect domestic species (L. interrogans serovars icterohaemorrhagiae/copenhagenai, hardjo, grippotyphosa, and canicola),2,5 are included in most L. interrogans serologic panels. In the present cases, none of the animals had titers to these serovars. However, some had titers to other L. interrogans serovars that were lower than those for L. interrogans serovar ballum. These lower titers probably reflect non-specific cross-reaction to the primary infecting serovar.2,4 If we had not employed a complete panel of Leptospira antigens, the Leptospira infection would probably not have been realized, or infection attributed to the wrong serovar. When investigating potential cases of Leptospira infection, we recommend that the serologic panel include serovars in addition to the classic L. interrogans pathogens. It is unlikely that prior vaccination would have protected against infection with L. interrogans serovar ballum because commercially available vaccines do not include this serovar and there is limited cross-protection between L. interrogans serovars.2,4 Although the source of infection was not determined, L. interrogans serovar ballum is commonly associated with the house mouse (Mus musculus) and black rat (Rattus rattus),4 and occasionally domestic cats (Felis catus).2 Both feral rodents and cats are known to be present on the grounds, and we suspect they may have been the source of infection. Alternately, the sea lions with low positive titers may have been asymptomatic carriers and transmitted the infection to the other animals.
Acknowledgments
The authors are grateful to Dr. Tracy Clippinger and the New York Aquarium Training and Sea Cliffs staffs for their assistance in animal care. We also thank Drs. Martin Haulena and Frances M.D. Gulland for consultation regarding treatment options.
References
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