Molecular detection of Ehrlichia canis and Rickettsia rickettsii in tick-infested dogs from the city of Chihuahua, Mexico: phylogenetic analysis of the gp36 and ompA genes.

Vector-borne diseases in dogs are an emerging problem worldwide due to their frequency, morbidity, and zoonotic relevance. Since there are no previous studies determining the frequency of Ehrlichia canis and Rickettsia rickettsii infection in three neighborhoods of the city of Chihuahua, Mexico, using molecular detection techniques, the objective of the present study was to detect, by nested polymerase chain reaction (PCR), a fragment of the gp36 gene of E. canis and the ompA gene of R. rickettsii in tick-infested dogs captured at the canine control center of the city of Chihuahua, and to phylogenetically analyze the genotypes present. Blood samples were collected from 123 tick-infested dogs. DNA was extracted from peripheral blood leukocytes and used in nested PCR protocols. The results showed a positivity frequency of 16.2% (20/123) for E. canis and 3.2% (4/123) for R. rickettsii. Six sequenced samples corresponded to E. canis and four to R. rickettsii. Phylogenetic analysis showed a close relationship with sequences previously described in the United States. This is the first molecular identification confirming E. canis and R. rickettsii infection in tick-infested dogs from some neighborhoods of the Chihuahua city, Mexico.