Document Type

Thesis - University Access Only

Award Date

2008

Degree Name

Master of Science (MS)

Department / School

Biology

Abstract

Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be one of the most devastating diseases in the swine industry throughout the world. PRRSV is an enveloped, positive stranded RNA virus belonging to the family Arteriviridae, order Nidovirales. PRRSV has two major genome types, European-like (Type 1) and North American-like (Type 2). PRRSV has had a dramatic effect on the swine industry with losses estimated at $600 million each year. PRRSV causes late-term reproductive failure and severe respiratory disease in nursery and growing/finish pigs. It replicates in the pulmonary macrophages, invades the humoral immune system and can cause persistent infection in lymphatic tissues. Replication is restricted to the cytoplasm of the cell. The PRRSV genome is about 15 kb in length and contains nine open reading frames. The replicase-associated genes, ORFla and ORF lb, situated at 5' end of the genome, represent nearly 75% of the viral genome. The ORF la encoded polyprotein is predicted to be cleaved at 8 sites to form 9 end products: nspla, nspl~, and nsp2 to nsp8. Proteolytic cleavage of the ORF 1 b portion of the replicase generates products nsp9 though nspl2. The nsp products derived from ORF la possess proteolytic activities and are responsible for processing the other nsp cleavage products. ORFlb cleavage products are involved in virus transcription and replication. Because of the emergence of Type 1 and Type 2 PRRSV in the U.S., new diagnostic tools are essential for the swine industry in order to control the disease progression. A commercially available enzyme linked immunosorbent assay from IDEXX Laboratories, IDEXX HerdChek® PRRS 2XR ELISA, has become an industry standard to test for antibodies against PRRSV. However, unexpected false positive results require an alternative serological test. In this study, a highly immunogenic nsp, nsp7, was evaluated to determine the feasibility for diagnostic serology development. European nsp7 and North American nsp7 were used to develop a dual indirect ELISA. Validation of the nsp7 ELISA used sera from 1,029 animals infected with North American Type 2 PRRSV and 303 animals infected with US Type 1 PRRSV. Receiver operating characteristic (ROC) analysis of the data calculated a diagnostic sensitivity of 98.34% for Type 1 and 98.84% for Type 2 and a diagnostic specificity of 97 .70% Type 1 and 99.32% Type 2. This dual-ELISA would be useful to detect Type l and Type 2 PRRSV conveniently and effectively. This is a sensitive and specific assay to be used as an alternative to current available diagnostic tools.

Library of Congress Subject Headings

Porcine reproductive and respiratory syndrome

Swine -- Virus diseases

Viral antibodies

Viral proteins

Format

application/pdf

Number of Pages

112

Publisher

South Dakota State University

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