Transmission ofAnaplasma marginalebyBoophilus microplus: Retention of Vector Competence in the Absence of Vector-Pathogen Interaction

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Abstract
Whether arthropod vectors retain competence for transmission of infectious agents in the long-term absence of vector-pathogen interaction is unknown. We addressed this question by quantifying the vector competence of two tick vectors, with mutually exclusive tropical- versus temperate-region distributions, for genetically distinct tropical- and temperate-region strains of the cattle pathogenAnaplasma marginale. The tropical cattle tickBoophilus microplus, which has been eradicated from the continental United States for over 60 years, was able to acquire and transmit the temperate St. Maries (Idaho) strain ofA. marginale. Similarly, the temperate-region tickDermacentor andersoniefficiently acquired and transmitted the Puerto Rico strain ofA. marginale. There were no significant quantitative differences in infection rate or number of organisms per tick following feeding on cattle with persistent infections of eitherA. marginalestrain. In contrast, the significantly enhanced replication of the Puerto Rico strain in the salivary gland ofB. microplusat the time of transmission feeding is consistent with adaptation of a pathogen strain to its available vector. However, the transmission of both strains byB. microplusdemonstrates that adaptation or continual interaction between the pathogen and vector is not required for retention of vector competence. Importantly, the results clearly show that reestablishment of acaricide-resistantB. microplusin the United States would be associated withA. marginaletransmission.

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