An Unusual Genotype of Toxoplasma gondii is Common in California Sea Otters (Enhydra lutris nereis) and is Associated with Mortality
American Association of Zoo Veterinarians Conference 2004
Melissa A. Miller1,2, DVM, PhD; Michael E. Grigg3,4, PhD; Christine Kreuder2, VMD, PhD; Erick R. James4; Ann C. Melli2; P.R. Crosbie5, PhD; David A. Jessup1, DVM, MPVM, DACZM; John C. Boothroyd3, PhD; Debbie Brownstein1; Patricia A. Conrad2, DVM, PhD
1Marine Wildlife Veterinary Care and Research Center, California Department of Fish and Game, Santa Cruz, CA, USA; 2Wildlife Health Center, School of Veterinary Medicine, University of California, Davis, CA, USA; 3Department of Microbiology and Immunology, School of Medicine, Stanford University, Stanford, CA, USA; 4Infectious Diseases, Departments of Medicine and Microbiology and Immunology, University of British Columbia, Vancouver, BC, Canada; 5Department of Biology, California State University, Fresno, CA, USA
Abstract
Toxoplasma gondii-associated meningoencephalitis is a significant disease of California sea otters (Enhydra lutris nereis), responsible for 16% of total mortality in fresh, beachcast carcasses. Toxoplasma gondii isolates were obtained from 35 California otters necropsied between 1998 and 2002. Based on multi-locus PCR-RFLP and DNA sequencing at conserved genes (18s rDNA, ITS-1) and polymorphic genes (B1, SAG1, SAG3 and GRA6), two distinct genotypes were identified: type II and a novel genotype, here called type x, that possessed distinct alleles at three of the four polymorphic loci sequenced. The majority (60%) of sea otter T. gondii infections were of genotype x, with the remaining 40% being of genotype II. No type I or type III genotypes were identified. Epidemiologic methods were used to examine the relationship between isolated T. gondii genotype(s) and spatial and demographic risk factors, such as otter stranding location and gender, as well as specific outcomes related to pathogenicity, such as severity of brain inflammation on histopathology and T. gondii-associated mortality. Differences were identified with respect to T. gondii genotype and sea otter gender and stranding location along the California coast. Localized spatial clustering was detected for both type II (centered within Monterey Bay) and type x (centered near Morro Bay)-infected otters. The Morro Bay cluster of type x-infected otters overlaps previously reported high-risk areas for sea otter infection and mortality due to T. gondii. Nine of 12 otters that had T. gondii-associated meningoencephalitis as a primary cause of death were infected with type x parasites.