Document Type

Dissertation - University Access Only

Award Date

2004

Degree Name

Doctor of Philosophy (PhD)

Department / School

Biology and Microbiology

Abstract

The recent emergence of a group of Type 1 European-like PRRSV in the U. S. has raised a new disease challenge for swine industry that has already been devastated by the traditional North American Type 2 PRRSV. The studies presented in this dissertation provide fundamental genetic and antigenic characterization of this group of European-like PRRSV, which is required for future development of effective vaccine and control strategies. The complete nucleotide sequence of genomic RNA of a North American Type 1 PRRSV index strain, EuroPRRSV, was determined. It shares 95.3% nucleotide sequence identity with European Type 1 prototypic strain, Lelystad, but only 61% with North American Type 2 prototypic strain, VR 2332. Its genome is the shortest among the published complete sequences of PRRSV, due to a 17 amino acid deletion in the Nsp2 encoding region. Compared to Nsp2 of sixteen North American Type 1 European-like PRRSV isolates from wide geographic distribution areas, the same 17 amino acid deletion was consistently identified in fourteen isolates. Peptide sequence analysis showed that areas in Nsp2 with deletions and amino acid hypervariability localize to regions that are predicted to immunologically important. The peptide sequence diversity, in the form of hypervariability and deletions in Nsp2, demonstrates that type 1 isolates in the U. S. represent a heterogeneous group. Phylogenic analysis using sixteen Type 1 isolates from wide geographic areas in the U. S. further demonstrated that this group of viruses forms a unique monomorphic clade containing at least three separate groups, which can also be identified based on deletions in Nsp2. The evolutionary relationship among the European -like PRRSV isolates in the U.S. are largely derived from a single Lelystad-like isolate. Genetic distance comparisons showed that these U. S. European-like Type 1 PRRSV isolates are the most recently evolved members of PRRSV. Antigenic studies using 60 monoclonal antibodies against structural proteins showed results consistent with the phylogenic analysis and demonstrated that these Type 1 isolates in the U. S. possess different antigenic profiles than typical European Type 1 isolates. These unique genetic and anigenic characteristics of European-like Type 1 PRRSV isolates in the U.S. indicate a new emerging disease threat to American swineherds.

Library of Congress Subject Headings

Porcine reproductive and respiratory syndrome -- Molecular aspects.
Swine -- Virus diseases -- United States.

Publisher

South Dakota State University

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Rights Statement

In Copyright