Temperate and tropical lineages of brown dog ticks in North America

Recent studies document that brown dog ticks, previously considered as Rhipicephalus sanguineus, are actually comprised of multiple taxonomic units now referred to as Rhipicephalus sanguineus sensu lato (Rssl); two lineages of Rssl have been described in the Americas to date - tropical and temperate. To identify the lineage of Rssl from dogs or premises at multiple sites in the United States and the Caribbean, we evaluated ticks (n=191) collected from several geographic locations (n=21), including Arizona, California, Florida, Hawaii, Illinois, Oklahoma, and Texas in the United States, and from Haiti. All ticks were identified as brown dog ticks by morphologic examination and comparison to standard keys. Sequence analysis of 12S rRNA mitochondrial gene fragments confirmed the presence of both lineages, with the Rssl tropical lineage predominating in Florida, Haiti, Hawaii, and far southern Texas (n=9 locations) and the Rssl temperate lineage present in California, Oklahoma, and Texas (n=12 locations). Mixed populations were not identified although the temperate lineage appeared to separate into two distinct clades. Analysis of additional brown dog tick specimens from the region will allow more complete understanding of the full extent of diversity in the R. sanguineus complex and likely has important implications for disease transmission, including zoonotic risk.