title: Strain composition of the ehrlichia Anaplasma marginale within persistently infected cattle, a mammalian reservoir for tick transmission.
abstract: Tick-borne ehrlichial pathogens of animals and humans require a mammalian reservoir of infection from which ticks acquire the organism for subsequent transmission. In the present study, we examined the strain structure of Anaplasma marginale, a genogroup II ehrlichial pathogen, in both an acute outbreak and in persistently infected cattle that serve as a reservoir for tick transmission. Using the msp1alpha genotype as a stable strain marker, only a single genotype was detected in a disease outbreak in a previously uninfected herd. In contrast, a diverse set of genotypes was detected in a persistently infected reservoir herd within a region where A. marginale is endemic. Genotypic diversity did not appear to be rapidly generated within an individual animal, because only a single genotype, identical to that of the inoculating strain, was detected at time points up to 2 years after experimental infection, and only a single identical genotype was found in repeat sampling of individual naturally infected cattle. Similarly, only a single genotype, identical to that of the experimentally inoculated St. Maries or South Idaho strain, was identified in the bloodmeal taken by Dermacentor andersoni ticks, in the midgut and salivary glands of the infected ticks, and in the blood of acutely infected cattle following tick transmission. The results show that mammalian reservoirs harbor genetically heterogeneous A. marginale and suggest that different genotypes are maintained by transmission within the reservoir population.
authors.affiliation: Program in Vector-borne Diseases, Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington 99164-7040, USA. gpalmer@vetmed.wsu.edu
authors.forename: G H
authors.initials: GH
authors.lastname: Palmer
authors.forename: F R
authors.initials: FR
authors.lastname: Rurangirwa
authors.forename: T F
authors.initials: TF
authors.lastname: McElwain
mesh_terms: D000595:Amino Acid Sequence; D000709:Anaplasma / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D000712:Anaplasmosis / Q000382:microbiology* / Q000635:transmission; D000818:Animals; D002417:Cattle; D004197:Disease Reservoirs / Q000662:veterinary*; D005819:Genetic Markers; D014644:Genetic Variation; D005838:Genotype; D008969:Molecular Sequence Data; D009922:Oregon; D016133:Polymerase Chain Reaction / Q000379:methods; D020449:Repetitive Sequences, Amino Acid; D015203:Reproducibility of Results; D013987:Ticks / Q000382:microbiology; D014481:United States
chemical_list: D005819:Genetic Markers