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Infection and Immunity, January 2009, p. 70-75, Vol. 77, No. 1
0019-9567/09/$08.00+0     doi:10.1128/IAI.01164-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Quantitative Differences in Salivary Pathogen Load during Tick Transmission Underlie Strain-Specific Variation in Transmission Efficiency of Anaplasma marginale{triangledown}

Massaro W. Ueti,1* Donald P. Knowles,1,2 Christine M. Davitt,3 Glen A. Scoles,2 Timothy V. Baszler,1 and Guy H. Palmer1

Program in Vector-Borne Diseases, Department of Veterinary Microbiology and Pathology and School for Global Animal Health, Washington State University, Pullman, Washington 99164,1 Animal Diseases Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Pullman, Washington 99164,2 Franceschi Microscopy and Imaging Center, Washington State University, Pullman, Washington 991643

Received 17 September 2008/ Returned for modification 7 October 2008/ Accepted 20 October 2008

The relative fitness of arthropod-borne pathogens within the vector can be a major determinant of pathogen prevalence within the mammalian host population. Strains of the tick-borne rickettsia Anaplasma marginale differ markedly in transmission efficiency, with a consequent impact on pathogen strain structure. We have identified two A. marginale strains with significant differences in the transmission phenotype that is effected following infection of the salivary gland. We have proposed competing hypotheses to explain the phenotypes: (i) both strains are secreted equally, but there is an intrinsic difference in infectivity for the mammalian host, or (ii) one strain is secreted at a significantly higher level and thus represents delivery of a greater pathogen dose. Quantitative analysis of pathogen replication and secretion revealed that the high-efficiency St. Maries strain replicated to a 10-fold-higher titer and that a significantly greater percentage of infected ticks secreted A. marginale into the saliva and did so at a significantly higher level than for the low-efficiency Israel vaccine strain. Furthermore, the transmission phenotype of the vaccine strain could be restored to that of the St. Maries strain simply by increasing the delivered pathogen dose, either by direct inoculation of salivary gland organisms or by increasing the number of ticks during transmission feeding. We identified morphological differences in the colonization of each strain within the salivary glands and propose that these reflect strain-specific differences in replication and secretion pathways linked to the vector-pathogen interaction.

* Corresponding author. Mailing address: Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164-7040. Phone: (509) 335-6325. Fax: (509) 335-8328. E-mail: massaro{at}vetmed.wsu.edu

{triangledown} Published ahead of print on 27 October 2008.

Editor: R. P. Morrison

Infection and Immunity, January 2009, p. 70-75, Vol. 77, No. 1
0019-9567/09/$08.00+0     doi:10.1128/IAI.01164-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Galletti, M. F. B. M., Ueti, M. W., Knowles, D. P. Jr., Brayton, K. A., Palmer, G. H. (2009). Independence of Anaplasma marginale Strains with High and Low Transmission Efficiencies in the Tick Vector following Simultaneous Acquisition by Feeding on a Superinfected Mammalian Reservoir Host. Infect. Immun. 77: 1459-1464 [Abstract] [Full Text]  


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