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Title: Anaplasma marginale superinfection attributable to pathogen strains with distinct genomic backgrounds.

item VALLEJO, EDUARDO - Washington State University
item Herndon, David
item MENDOZA, FRANCISCO - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP)
item MOSQUEDA, JUAN - Autonomous University Of Querétaro
item PALMER, GUY - Washington State University

Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2014
Publication Date: 10/6/2014
Citation: Vallejo, E., Herndon, D.R., Mendoza, F., Mosqueda, J., Palmer, G. 2014. Anaplasma marginale superinfection attributable to pathogen strains with distinct genomic backgrounds. Infection and Immunity. 82(12):5286-5292.

Interpretive Summary: Anaplasmosis is a disease of cattle with worldwide distribution and high prevalence in tropical regions. The bacterium is transmitted by tick-bites and other herd management practices. Research efforts to combat the disease focus on controlling the tick vector and developing effective vaccines to prevent infection and/or disease. Understanding how multiple different strains infect the same bovine host (a phenomenon known as super infection) may lead to improved vaccines, treatment options and disease prevention strategies. We used high-throughput sequencing of a panel of genes that effectively distinguishes known strains to study the diversity of the pathogen population in geographically different regions. Our results show a greater level of diversity in population structure in tropical vs. temperate regions and suggest that super infection likely occurs when different strains infect the same animal, rather than alterations of the original strain. The long term impact of this work is the development of a system that can catalog and characterize the population structure of Anaplasma marginle.

Technical Abstract: Microbial strain structure is dynamic over space and time; shifts in pathogen strain structure result in changing patterns of disease. The scale of change in space and time differs markedly among pathogens depending on multiple factors including pathogen-specific mechanisms of genetic change and the strength of the selective pressure. In endemic regions with high prevalence of infection, broad population immunity develops against Anaplasma marginale, a highly antigenically variant rickettsial pathogen, and creates strong selective pressure for emergence of and superinfection with strains that differ in their Msp2 variant repertoire. The strains may emerge either by msp2 locus duplication and allelic divergence on an existing genomic background or by introduction of a strain with a different msp2 allelic repertoire on a distinct genomic background. To answer this question, we developed a multi-locus typing assay, based on high throughput sequencing of non-msp2 target loci, to distinguish among strains on different genomic backgrounds. The technical error level was statistically defined based on the percentage of perfect reads of clones of each target locus and validated using experimental single strains and strain pairs. Testing of A. marginale positive samples from endemic tropical regions identified individual infections that contained unique alleles for all five targeted loci. The data revealed a highly significant difference in the number of strains per animal in the tropical regions as compared to infections in temperate regions and strongly supported the hypothesis that transmission of genomically distinct A. marginale strains predominates in high prevalence endemic areas.