Tick Transmission of Anaplasma marginale

Abstract

Anaplasma marginale is a globally prevalent pathogen of cattle transmitted by Ixodid ticks. Understanding the complex development of A. marginale in the tick vector will allow for better prediction of disease outbreaks and will afford opportunities for control of disease transmission. The basic developmental cycle of A. marginale in the tick is reviewed here along with recent studies exploiting differences in transmission between strains to delineate aspects of the interaction between the pathogen and the vector. Bacterial, protozoan, and viral pathogens transmitted by arthropod vectors result in severe disease in animals and humans. Despite their impact, these infections remain poorly controlled with primary reliance on acaricides to block tick transmission. The rapid emergence of tick resistance to multiple acaricides threatens this control and has resulted in a resurgence of research to develop novel strategies for control. Novel approaches to preventing tick-borne transmission of livestock pathogens will result from understanding the interaction between the pathogen and the tick, a process that culminates with development of infectivity and successful transmission. In all of the tick-transmitted pathogens, development of pathogen infectivity is coordinated with attachment and feeding of the tick upon the animal. This is clearly dependent upon signaling between the feeding vector and the pathogen and thus susceptible to intervention.