Article Category:
Research Article

Rickettsial Pathogens in Dogs and Ticks During an Epidemic of Rocky Mountain Spotted Fever in Ensenada, Baja California, México

Laura Backus School of Veterinary Medicine, University of California, Davis, California;
Department of Animal Science, California Polytechnic University, San Luis Obispo, California;

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Francesca Rubino School of Veterinary Medicine, University of California, Davis, California;

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Andrés M. López-Pérez School of Veterinary Medicine, University of California, Davis, California;
Red de Biología y Conservación de Vertebrados, Instituto de Ecología, A.C, Xalapa, México;

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Oscar E. Zazueta Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, Massachusetts;
Departamento de Epidemiología, Secretaría de Salud de Baja California, Mexicali, México;

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Javier Borboa Departamento de Epidemiología, Secretaría de Salud de Baja California, Mexicali, México;

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Alexa C. Quintana Viral and Rickettsial Disease Laboratory, Center for Laboratory Sciences, California Department of Public Health, Richmond, California;

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Will Probert Viral and Rickettsial Disease Laboratory, Center for Laboratory Sciences, California Department of Public Health, Richmond, California;

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Jill K. Hacker Viral and Rickettsial Disease Laboratory, Center for Laboratory Sciences, California Department of Public Health, Richmond, California;

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Paola Gómez-Castellanos Departamento de Epidemiología, Secretaría de Salud de Baja California, Mexicali, México;

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Leslie C. Inustroza-Sánchez Departamento de Epidemiología, Secretaría de Salud de Baja California, Mexicali, México;

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Claudia Herrera Olivas Departamento de Ecología, Fauna Silvestre y Animales de Laboratorio, Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional Autónoma de México, México City, México;

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Christopher D. Paddock Rickettsial Zoonoses Branch, Centers for Disease Control and Prevention, Atlanta, Georgia

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Janet Foley School of Veterinary Medicine, University of California, Davis, California;

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DOI:
https://doi.org/10.4269/ajtmh.24-0497
Volume/Issue:
Ahead of Print
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A Rocky Mountain spotted fever (RMSF) epidemic has spread through the state of Baja California, Mexico over the last decade and a half, beginning in Mexicali, and subsequently to Tijuana and to Ensenada by 2018. In October of 2022, we surveyed dogs and homes in randomly selected Áreas Geoestadisticas Básicas (AGEBs) with and without reported human cases. Brown dog ticks (Rhipicephalus sanguineus sensu lato) were found on 33.9% of dogs and in the yards of 23.6% of homes. Homes from AGEBs with cases had over a 6-fold increased odds of ticks being present in the yard than AGEBs without reported cases. Both dogs that were permitted to roam and the presence of roaming dogs in the neighborhood were strongly associated with tick infestation of dogs and homes. No ticks or blood samples were polymerase chain reaction-positive for Rickettsia (R.) rickettsii, the causative agent of RMSF, although 54.6% of dogs were seropositive for spotted fever group rickettsiae, and 17.4% were seropositive for typhus group rickettsiae. R. massiliae and R. felis were detected in eight (1.3%) and 29 (4.8%) ticks, respectively; and R. felis was also detected in eight (4.6%) dog blood samples. Although the pathogenic potential of these other rickettsial species and their role in RMSF transmission remains unclear, our data on tick burdens in dogs and homes as risk factors for RMSF exposure provide further support to the pivotal need to reduce tick burdens and the numbers of roaming dogs to successfully manage the RMSF epidemic in northern Mexico.

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Author Notes

Financial support: Financial support was provided by the University of California, Davis School of Veterinary Medicine.

Disclosures: The findings and conclusions are those of the authors and do not necessarily reflect the official views of position of the California Department of Public Health, the California Health and Human Services Agency, or the CDC. No authors have real or perceived conflicts of interest.

Current contact information: Laura Backus, Department of Animal Science, California Polytechnic University, San Luis Obispo, CA, E-mail: lbackus@calpoly.edu. Francesca Rubino and Janet Foley, School of Veterinary Medicine, University of California, Davis, CA, E-mails: firubino@ucdavis.edu and jefoley@ucdavis.edu. Andrés M. López-Pérez, Red de Biología y Conservación de Vertebrados, Instituto de Ecología, A.C., Xalapa, México, E-mail: amlope@ucdavis.edu. Oscar E. Zazueta, Department of Epidemiology, Harvard T.H. Chan School of Public Health, Boston, MA, E-mail: oez512@mail.harvard.edu. Javier Borboa, Paola Gómez-Castellanos, and Leslie C. Inustroza-Sánchez, Departamento de Epidemiología, Secretaría de Salud de Baja California, Mexicali, México, E-mail: javier.borboa@uabc.edu.mx, paogomez8714@gmail.com, and lesliecarolina55@gmail.com. Alexa C. Quintana, Will Probert, and Jill K. Hacker, Viral and Rickettsial Disease Laboratory, Center for Laboratory Sciences, California Department of Public Health, Richmond, CA, E-mails: alexa.quintana@cdph.ca.gov, will.probert@cdph.ca.gov, and jill.hacker@cdph.ca.gov. Claudia Herrera Olivas, Departamento de Ecología, Fauna Silvestre y Animales de Laboratorio, Facultad de Medicina Veterinaria y Zootecnia, Universidad Nacional Autónoma de México, México City, México, E-mail: aliciaherrera.25.94@gmail.com. Christopher D. Paddock, Rickettsial Zoonoses Branch, CDC, Atlanta, GA, E-mail: cdp9@cdc.gov.

Address correspondence to Janet Foley, School of Veterinary Medicine, University of California, 944 Garrod Dr, Davis, CA 95616. E-mail: jefoley@ucdavis.edu
Copyright:
© American Society of Tropical Medicine and Hygiene 2025
Received:
22 Jul 2024
|
Accepted:
13 Nov 2024
|
Published Online:
18 Feb 2025
Cover The American Journal of Tropical Medicine and Hygiene
The American Journal of Tropical Medicine and Hygiene
Print ISSN:
0002-9637
Online ISSN:
1476-1645

Expert Committee on Hepatitis

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