Roaming Dogs, Intense Brown Dog Tick Infestation, and Emerging Rocky Mountain Spotted Fever in Tijuana, Mexico.

Foley J., et al. Am. J. Trop. Med. Hyg., 00(00), 2024, pp. 1–16 doi:10.4269/ajtmh.23-0410

Abstract. A two decades–long epidemic of Rocky Mountain spotted fever in northern Mexico reached the U.S. border city of Tijuana in 2021. Cases were near the city periphery in marginalized areas, some lacking infrastructure such as streets or utilities. We worked in the three census areas where human cases were reported and in 12 additional control Areas Geoestadisticas Basicas. Of 191 examined dogs, 61.8% were tick-infested, with 6-fold increased odds if they were allowed to roam. Although no dogs were Rickettsia polymerase chain reaction–positive, we found one R. rickettsii and 11 Rickettsia massiliae–infected ticks. The rickettsial IgG seroprevalence by immunofluorescence antibody assay was 76.4%, associated with unhealthy body condition, adults, dogs with> 10 ticks, more dogs being seen in the area, and dogs being permitted in the street. Insufficient medical and canine management resources have contributed to a case fatality rate of RMSF that has exceeded 50% in areas. High canine seroprevalence suggests risks to people and dogs; unfortunately, herd immunity is impeded by high turnover in the canine population owing to the birth of puppies and high death rates. Binational One Health workers should monitor disease spread, enact canine population management and tick eradication, and provide prevention, diagnostic, and treatment support.

Note: Abandoning dogs in Mexico by legal and illegal immigrants may only add to this public health issue and perhaps provide some risk for border communities.