First Molecular Detection of the Potential Zoonotic Pathogen Rickettsia asembonensis in Client-Owned Dogs and Cats in Thailand

Abstract

Introduction: Rickettsioses are predominantly zoonotic infections that circulate among animal populations and can be transmitted to humans, representing emerging vector-borne diseases spread through infected arthropod vectors. Rickettsia asembonensis displays a broad geographic distribution and is predominantly associated with fleas. Recent reports have identified R. asembonensis in febrile human patients in Malaysia, Peru, and Zambia, underscoring its emerging zoonotic potential. In Thailand, however, investigations of Rickettsia spp. have concentrated mainly on ticks and fleas, with comparatively little information regarding infections in pet dogs and cats. Methods: The present study examined Rickettsia spp. in 968 pets, 472 client-owned dogs, and 496 client-owned cats from the Bangkok and Nakhon Pathom regions, using the 17-kDa gene as a molecular marker. Genetic analyses of Rickettsia species were performed using maximum-likelihood phylogeny with IQ-TREE, Bayesian inference, pairwise sequence similarity assessment, and nucleotide sequence type network analysis. Results: A total of 114 pets tested positive, corresponding to a prevalence of 11.8%, with 21.6% (102/472) in dogs and 2.4% (12/496) in cats. Of these, 48 samples were sequenced, leading to the identification of R. asembonensis and either uncultured Rickettsia spp. or the Rickettsia endosymbiont of Haemaphysalis bispinosa. Statistical analysis indicated significantly higher infection rates in pet dogs and cats from the Nakhon Pathom region. Phylogenetic reconstruction with maximum-likelihood and Bayesian-inference approaches revealed distinct clustering of R. asembonensis and uncultured Rickettsia spp. Furthermore, three nucleotide sequence types of R. asembonensis identified here were unique and not shared with isolates from other countries or host species, as demonstrated by phylogenetic and Templeton–Crandall–Sing network analyses. Conclusions: This work provides the first documentation of R. asembonensis in client-owned urban dogs and cats in Thailand and highlights the need for increased awareness among veterinarians and pet owners, given its public health relevance.