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Infection and Immunity, April 2009, p. 1459-1464, Vol. 77, No. 4
0019-9567/09/$08.00+0     doi:10.1128/IAI.01518-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

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{triangledown}

Maria F. B. M. Galletti,1 Massaro W. Ueti,1 Donald P. Knowles Jr.,1,2 Kelly A. Brayton,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 991642

Received 15 December 2008/ Returned for modification 14 January 2009/ Accepted 26 January 2009

Strain superinfection occurs when a second pathogen strain infects a host already carrying a primary strain. Anaplasma marginale superinfection occurs when the second strain carries a variant repertoire different from that of the primary strain, and the epidemiologic consequences depend on the relative efficiencies of tick-borne transmission of the two strains. Following strain superinfection in the reservoir host, we tested whether the presence of two A. marginale (sensu lato) strains that differed in transmission efficiency altered the transmission phenotypes in comparison to those for single-strain infections. Dermacentor andersoni ticks were fed on animals superinfected with the Anaplasma marginale subsp. centrale vaccine strain (low transmission efficiency) and the A. marginale St. Maries strain (high transmission efficiency). Within ticks that acquired both strains, the St. Maries strain had a competitive advantage and replicated to significantly higher levels than the vaccine strain. The St. Maries strain was subsequently transmitted to naïve hosts by ticks previously fed either on superinfected animals or on animals singly infected with the St. Maries strain, consistent with the predicted transmission phenotype of this strain and the lack of interference due to the presence of a competing low-efficiency strain. The vaccine strain was not transmitted by either singly infected or coinfected ticks, consistent with the predicted transmission phenotype and the lack of enhancement due to the presence of a high-efficiency strain. These results support the idea that the strain predominance in regions of endemicity is mediated by the intrinsic transmission efficiency of specific strains regardless of occurrence of superinfection.

* Corresponding author. Mailing address: Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA 99164-7040. Phone: (509) 335-6033. Fax: (509) 335-8529. E-mail: gpalmer{at}vetmed.wsu.edu

{triangledown} Published ahead of print on 2 February 2009.

Editor: R. P. Morrison

Infection and Immunity, April 2009, p. 1459-1464, Vol. 77, No. 4
0019-9567/09/$08.00+0     doi:10.1128/IAI.01518-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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