Molecular detection of Coxiella endosymbionts associated with ixodid ticks recovered from animals and man in Mexico: Phylogeography and haplotype diversity analysis

Abstract

For over 80 years, the genus Coxiella was considered monotypic, comprising only Coxiella burnetii, the aetiological agent of Q fever. Recent studies, however, have revealed several candidate species and genetic lineages associated with ticks, many of which act as endosymbionts that are essential for tick development. This association is particularly notable in the members of the Rhipicephalus sanguineus complex, where Candidatus Coxiella massiliensis (zoonotic) and Candidatus Coxiella mudrowiae (unknown pathogenicity) have been described. Given the close relationship between these ticks, domestic dogs, and humans, active surveillance for Coxiella species of medical and veterinary importance is crucial.

This study evaluated the presence and diversity of Coxiella species in 812 hard ticks: Amblyomma mixtum (n = 23), Rhipicephalus linnaei (n = 762), and R. sanguineus sensu stricto (n = 27) collected from December 2018 to November 2024 parasitizing dogs (n = 418), humans (n = 18), cattle (n = 4), and one cat across 17 states of Mexico.

A fragment (∼1500 base pair) of the Coxiella 16S ribosomal DNA (rDNA) gene was amplified, sequenced, and analysed phylogenetically. Additionally, published records of Coxiella endosymbionts associated with ticks parasitising dogs were compiled. Of 812 samples, 188 tested positive, revealing three Coxiella lineages closely related to known endosymbionts of Rhipicephalus and Amblyomma ticks. A review of 25 studies from across the globe identified four Coxiella taxa in 23 tick species from dogs across 19 countries. This is the first report of Coxiella lineages in dog-associated ticks in Mexico. Our findings expand the known diversity of the genus in the Neotropical region and underscore the need for further research to clarify their ecological roles and potential health implications.