, Volume 10, Issue 3, pp 277–289 | Cite as

Toxoplasma gondii, Source to Sea: Higher Contribution of Domestic Felids to Terrestrial Parasite Loading Despite Lower Infection Prevalence

  • Elizabeth VanWormer
  • Patricia A. Conrad
  • Melissa A. Miller
  • Ann C. Melli
  • Tim E. Carpenter
  • Jonna A. K. Mazet
Original Contribution


Environmental transmission of Toxoplasma gondii, a global zoonotic parasite, adversely impacts human and animal health. Toxoplasma is a significant cause of mortality in threatened Southern sea otters, which serve as sentinels for disease threats to people and animals in coastal environments. As wild and domestic felids are the only recognized hosts capable of shedding Toxoplasma oocysts into the environment, otter infection suggests land-to-sea pathogen transmission. To assess relative contributions to terrestrial parasite loading, we evaluated infection and shedding among managed and unmanaged feral domestic cats, mountain lions, and bobcats in coastal California, USA. Infection prevalence differed among sympatric felids, with a significantly lower prevalence for managed feral cats (17%) than mountain lions, bobcats, or unmanaged feral cats subsisting on wild prey (73–81%). A geographic hotspot of infection in felids was identified near Monterey Bay, bordering a high-risk site for otter infection. Increased odds of oocyst shedding were detected in bobcats and unmanaged feral cats. Due to their large populations, pet and feral domestic cats likely contribute more oocysts to lands bordering the sea otter range than native wild felids. Continued coastal development may influence felid numbers and distribution, increase terrestrial pathogens in freshwater runoff, and alter disease dynamics at the human–animal–environment interface.


Toxoplasma gondii feral cats mountain lions bobcats pathogen pollution zoonotic disease 



The authors acknowledge the outstanding collaboration and mutual support among regional animal shelters, wildlife rehabilitation personnel, academia, and state and federal wildlife protection agencies that made this work possible. In particular, we thank Carol Iida, Ila Davis, Kathy Prew, Cindy Burnham and California Department of Fish and Wildlife wardens for their generous support in sampling domestic and wild felids. We also thank staff from the Conrad Research Group at University of California, Davis, and the California Department of Fish and Wildlife Marine Veterinary Care and Research Center, especially Dave Jessup, Lexi Fisher, Adam Schneider, Tim Bernot, Diana Simoes, and Andrea Packham for invaluable assistance with sample collection and diagnostics. We are grateful to Idexx Laboratories, Inc. for providing FeLV/FIV diagnostic test kits at reduced cost. We also thank Andrew Breed and two anonymous reviewers for comments on an earlier draft of the manuscript. Grants from the National Science Foundation Ecology of Infectious Disease Program (0525765, 1065990) and a fellowship from the National Center for Foreign Animal and Zoonotic Disease Defense (to E. VanWormer) supported this research.


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Copyright information

© International Association for Ecology and Health 2013

Authors and Affiliations

  • Elizabeth VanWormer
    • 1
  • Patricia A. Conrad
    • 1
    • 2
  • Melissa A. Miller
    • 1
    • 3
  • Ann C. Melli
    • 2
  • Tim E. Carpenter
    • 4
  • Jonna A. K. Mazet
    • 1
  1. 1.Wildlife Health Center, One Health Institute, School of Veterinary MedicineUniversity of CaliforniaDavisUSA
  2. 2.Department of Pathology, Microbiology and Immunology, School of Veterinary MedicineUniversity of CaliforniaDavisUSA
  3. 3.California Department of Fish and WildlifeMarine Wildlife Veterinary Care and Research CenterSanta CruzUSA
  4. 4.EpiCentre, Massey UniversityPalmerston NorthNew Zealand

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