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Journal of Virology, May 2001, p. 4570-4583, Vol. 75, No. 10
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.10.4570-4583.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Equine Infectious Anemia Virus Genomic Evolution in Progressor and Nonprogressor Ponies

Caroline Leroux,1,dagger Jodi K. Craigo,1 Charles J. Issel,2 and Ronald C. Montelaro1,*

Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261,1 and Department of Veterinary Science, Gluck Equine Research Center, University of Kentucky, Lexington, Kentucky 405462

Received 20 November 2000/Accepted 16 February 2001

A primary mechanism of lentivirus persistence is the ability of these viruses to evolve in response to biological and immunological selective pressures with a remarkable array of genetic and antigenic variations that constitute a perpetual natural experiment in genetic engineering. A widely accepted paradigm of lentivirus evolution is that the rate of genetic variation is correlated directly with the levels of virus replication: the greater the viral replication, the more opportunities that exist for genetic modifications and selection of viral variants. To test this hypothesis directly, we examined the patterns of equine infectious anemia virus (EIAV) envelope variation during a 2.5-year period in experimentally infected ponies that differed markedly in clinical progression and in steady-state levels of viral replication as indicated by plasma virus genomic RNA assays. The results of these comprehensive studies revealed for the first time similar extents of envelope gp90 variation in persistently infected ponies regardless of the number of disease cycles (one to six) and viremia during chronic disease. The extent of envelope variation was also independent of the apparent steady-state levels of virus replication during long-term asymptomatic infection, varying from undetectable to 105 genomic RNA copies per ml of plasma. In addition, the data confirmed the evolution of distinct virus populations (genomic quasispecies) associated with sequential febrile episodes during acute and chronic EIA and demonstrated for the first time ongoing envelope variation during long-term asymptomatic infections. Finally, comparison of the rates of evolution of the previously defined EIAV gp90 variable domains demonstrated distinct differences in the rates of nucleotide and amino acid sequence variation, presumably reflecting differences in the ability of different envelope domains to respond to immune or other biological selection pressures. Thus, these data suggest that EIAV variation can be associated predominantly with ongoing low levels of virus replication and selection in target tissues, even in the absence of substantial levels of plasma viremia, and that envelope variation continues during all stages of persistent infection as the virus successfully avoids clearance by host defense mechanisms.


* Corresponding author. Mailing address: Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261. Phone: (412) 648-8869. Fax: (412) 383-8859. E-mail: rmont{at}pitt.edu.

dagger Present address: UMR 754 INRA/Université Claude Bernard/ Ecole Nationale Vétérinaire de Lyon, Laboratoire d'Immunologie et de Biologie Pulmonaire, Hôpital Louis Pradel, 69003 Lyon, France.


Journal of Virology, May 2001, p. 4570-4583, Vol. 75, No. 10
0022-538X/01/$04.00+0   DOI: 10.1128/JVI.75.10.4570-4583.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



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