Whether arthropod vectors retain competence for transmission of infectious agents in

Whether arthropod vectors retain competence for transmission of infectious agents in the long-term absence of vector-pathogen interaction is unknown. in regions where the tropical cattle fever tick is endemic (19, 21, 25, 28). Larval, nymphal, and adult stages of this tick all preferentially feed on cattle, and each can efficiently acquire and transmit (1, 24). This high vectorial capacity of results in most calves in subtropical and tropical regions being infected within the first year of life, and this high incidence represents a severe constraint on animal health and production (11). Remarkably, was eradicated from the continental United States by a mandatory acaricide-based program initiated in 1906, and eradication status is maintained by required acaricide treatment of cattle entering or resident within a quarantine zone along the U.S.-Mexico border (10). Since eradication, tick transmitting of in america is mediated by and prevalence in the United States since eradication is markedly lower than in regions where is the primary vector (17, 30, 32). The likelihood of reestablishing its previous range in the U.S. has been markedly increased by the emergence in Mexico of ticks resistant to multiple acaricides, including those used to maintain the 80-mile quarantine region (3, 4). Reestablishment of spp. (17, 23, 30). Assessment of this risk requires determining whether has retained vector competence: that is the ability to acquire and transmit to the United States temperate-region strains of in the long-term absence of pathogen-vector interaction. strains have well-characterized genotypic and phenotypic differences (23): notably, strains naturally transmitted by form a distinct genetically defined clade as compared to temperate-region strains transmitted by spp. (5). In the 60 years since eradication of the cattle fever tick in the 1940s, any strains dependent upon tick transmission by would have been lost Ticagrelor from the cattle population, as is suggested by the distinct clade structures. The ability of the tick vector to acquire from a persistently infected animal is influenced by the level of rickettsemia during feeding, and not all fed ticks become infected (7). The failure Ticagrelor of the ticks to become infected appears to occur at the level of the midgut (26), consistent with the importance of a midgut barrier to infection. Successful acquisition of is unknown; however, a markedly reduced ability of to acquire temperate-region strains of during feeding on persistently infected cattle would result in the reduction or loss of vector competence. Following invasion of the midgut epithelium, undergoes initial intracellular replication in the midgut epithelial cells and progresses to invasion of the salivary glands (14). Within the salivary glands, a second round of replication occurs and culminates in development of infectious organisms during transmission feeding (15, 18, 26). In adult male ticks infected with the temperate-region South Idaho strain of and fed on cattle Ticagrelor persistently infected with either a tropical-region strain or a temperate-region strain and determine whether pathogen transmission by each vector is restricted to the genetically and geographically defined clades. MATERIALS AND METHODS Pathogen and vector strains. and naturally transmit the Puerto Rico and St. Maries (Idaho) strains of gene assigns it to a clade of temperate-region strains (6), while the sequence of the Puerto Rico gene (obtained from infected ticks [GenBank accession no. “type”:”entrez-nucleotide”,”attrs”:”text”:”AY191827″,”term_id”:”28569526″AY191827]) places it within a clade of seven strains TRIB3 from regions of Ticagrelor endemicity as reported by de la Fuente et al. (6). The La Minita strain of and the Reynolds Creek strain of and other pathogens, were maintained at the USDA Agricultural Research.