Borrelia burgdorferisensu lato infection has been confirmed in clinical cases in the northeast of Mexico; however, the bacterium has not been identified as infecting the tick vector Ixodes, Amblyomma and Dermacentor ticks were collected from mammals and plants in northeastern Mexico and examined for Borrelia. Eighteen of 214 ticks were PCR-positive for the fla and 16S rRNA genes and 15 for the ospA gene. Southern blotting with a fla probe and sequencing of ospA genes confirmed infection with B. burgdorferi sensu stricto. These findings, together with reports of indigenous cases, fulfil the criteria that allow northeastern Mexico to be considered as a zone endemic for Lyme disease.

Phylogenetic relationships among 18 samples from nine nominal species of Geomylichus (Acari: Listrophoridae), were analyzed based on internal transcribed spacer 2 (ITS 2) sequences, Prolistrophorus sp. was used as an outgroup. Maximum likelihood and neighbor-joining analyses indicated that Geomylichus is formed by at least three internal clades. Genetic distance among Prolistrophorus and Geomylichus was 27.8-35.5%, and among species, populations, and infrapopulations of Geomylichus it was 0.4-21.8%, 0.8-2.4%, and 0.8-1.2%, respectively. Differences between the results of this analysis with conventional taxonomy of the group, as well as the overlapping of genetic distances among species, populations, and infrapopulations, suggest that the definition of species within Geomylichus deserves reconsideration. For example, the recognition of inconsistencies among G. texanus populations associated to different host species, resulting from the molecular analysis, led us to collect new morphological evidence now suggesting that this taxon represents more than one species.

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Tick-Borne Rickettsial Diseases (TBRD) are emerging zoonotic diseases, and a problem of human health and veterinary medication. The distribution of these diseases is related to the distribution of vector. The presence of pathogens in the host is a risk indicator of population exposure to these areas. A total of 478 tissues samples from rodents, A. phagocytophilum 18 (3.7%), E. canis 47 (9.8%), Rickettsia rickettsii 18 (3.7%) and E. chaffeensis 19 (3.9%) were detected using speciesspecific PCR assay. It is the first report in Mexico the presence of rodents infected with A. phagocytophilum and E. chaffeensis. The rodent Peromyscus spp. were the most commonly prevalent host of infection for all the bacteria's. We have to consider as host of TBRD transmitter and provide a useful contribution to understanding their epidemiology. The health sector should be considered all the fevers of unknown causes in humans and animals in Mexico as infections by these vector-borne rickettsial pathogens.

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