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      Transmisión de Anaplasma marginale por garrapatas Translated title: Tick Transmission of Anaplasma marginale

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          Abstract

          Anaplasma marginale, patógeno de distribución mundial, es transmitido por garrapatas Ixódidas. Comprender su complejo desarrollo dentro de la garrapata vector, permitirá la predicción de brotes y ofrecerá oportunidades para controlar su transmisión. En este trabajo se revisa su ciclo básico de desarrollo junto con los estudios recientes acerca de las diferencias de transmisión entre cepas, que delinean aspectos de la interacción patógeno - vector. Bacterias, virus o protozoarios transmitidos por artrópodos causan enfermedades severas, tanto en humanos como en animales. Las enfermedades infecciosas transmitidas por garrapatas, entre las que incluimos a la Anaplasmosis (A. marginale), babesiosis (Babesía bígemína, B. bovís, B. dívergens) y Theileriosis (Theileria annulata, T. parva), se encuentran entre las más importantes en el ámbito mundial, con pérdidas cercanas a los siete mil millones de dólares anualmente; y, a pesar de su impacto, permanecen escasamente bajo control, basado primordialmente en la aplicación de acaricidas, para interrumpir su transmisión. La aparición de garrapatas resistentes a múltiples sustancias acaricidas, representa una amenaza en este tipo de control y, como resultado, hay un resurgimiento de la investigación para el desarrollo de nuevas estrategias para su control. Nuevas opciones para prevenir la transmisión de patógenos de animales por garrapatas, será el resultado de entender las interacciones garrapata-patógeno; proceso que culmina con el desarrollo de la infección y transmisión exitosa. En todos los casos de patógenos transmitidos por garrapatas, el desarrollo de la infección se realiza coordinamente a los momentos de adhesión y alimentación del vector sobre el animal. Esto sucede por la interdependencia en la señalización entre el patógeno y el vector al alimentarse y, por ello, será susceptible de intervención.

          Translated 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.

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          Complete genome sequencing of Anaplasma marginale reveals that the surface is skewed to two superfamilies of outer membrane proteins.

          The rickettsia Anaplasma marginale is the most prevalent tick-borne livestock pathogen worldwide and is a severe constraint to animal health. A. marginale establishes lifelong persistence in infected ruminants and these animals serve as a reservoir for ticks to acquire and transmit the pathogen. Within the mammalian host, A. marginale generates antigenic variants by changing a surface coat composed of numerous proteins. By sequencing and annotating the complete 1,197,687-bp genome of the St. Maries strain of A. marginale, we show that this surface coat is dominated by two families containing immunodominant proteins: the msp2 superfamily and the msp1 superfamily. Of the 949 annotated coding sequences, just 62 are predicted to be outer membrane proteins, and of these, 49 belong to one of these two superfamilies. The genome contains unusual functional pseudogenes that belong to the msp2 superfamily and play an integral role in surface coat antigenic variation, and are thus distinctly different from pseudogenes described as byproducts of reductive evolution in other Rickettsiales.
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            Efficient use of a small genome to generate antigenic diversity in tick-borne ehrlichial pathogens.

            Ehrlichiae are responsible for important tick-transmitted diseases, including anaplasmosis, the most prevalent tick-borne infection of livestock worldwide, and the emerging human diseases monocytic and granulocytic ehrlichiosis. Antigenic variation of major surface proteins is a key feature of these pathogens that allows persistence in the mammalian host, a requisite for subsequent tick transmission. In Anaplasma marginale pseudogenes for two antigenically variable gene families, msp2 and msp3, appear in concert. These pseudogenes can be recombined into the functional expression site to generate new antigenic variants. Coordinated control of the recombination of these genes would allow these two gene families to act synergistically to evade the host immune response.
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              Identification of midgut and salivary glands as specific and distinct barriers to efficient tick-borne transmission of Anaplasma marginale.

              Understanding the determinants of efficient tick-borne microbial transmission is needed to better predict the emergence of highly transmissible pathogen strains and disease outbreaks. Although the basic developmental cycle of Anaplasma and Ehrlichia spp. within the tick has been delineated, there are marked differences in the ability of specific strains to be efficiently tick transmitted. Using the highly transmissible St. Maries strain of Anaplasma marginale in Dermacentor andersoni as a positive control and two unrelated nontransmissible strains, we identified distinct barriers to efficient transmission within the tick. The Mississippi strain was unable to establish infection at the level of the midgut epithelium despite successful ingestion of infected blood following acquisition feeding on a bacteremic animal host. This inability to colonize the midgut epithelium prevented subsequent development within the salivary glands and transmission. In contrast, A. marginale subsp. centrale colonized the midgut and then the salivary glands, replicating to a titer indistinguishable from that of the highly transmissible St. Maries strain and at least 100 times greater than that previously associated with successful transmission. Nonetheless, A. marginale subsp. centrale was not transmitted, even when a large number of infected ticks was used for transmission feeding. These results establish that there are at least two specific barriers to efficient tick-borne transmission, the midgut and salivary glands, and highlight the complexity of the pathogen-tick interaction.
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                Author and article information

                Journal
                rmcp
                Revista mexicana de ciencias pecuarias
                Rev. mex. de cienc. pecuarias
                Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (Mérida, Yucatán, Mexico )
                2007-1124
                2448-6698
                September 2012
                : 3
                : suppl 1
                : 41-50
                Affiliations
                [01] Pullman WA orgnameWashington State University orgdiv1School for Global Animal Health orgdiv2Department of Veterinary Microbiology and Pathology USA. kbrayton@ 123456vetmed.wsu.edu
                Article
                S2007-11242012000500006 S2007-1124(12)00300000006
                5bbdeb86-6499-44f8-aa9c-70761a4f1de4

                This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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                Figures: 0, Tables: 0, Equations: 0, References: 53, Pages: 10
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                SciELO Mexico

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                Anaplasma marginale,Transmission,Ticks,Garrapatas,Transmisión

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