Evidence for divergence of restriction fragment length polymorphism patterns following in vivo replication of porcine reproductive and respiratory syndrome virus

Ronald D. Wesley From the Virology Swine Research Unit, National Animal Disease Center, USDA, Agricultural Research Service P. O. Box 70, Ames, IA 50010 (Wesley, Mengeling, Lager, Vorwald), and Boehringer Ingelheim/NOBL Laboratories Inc 2501 N Loop Dr, Ames, IA 50010 (Roof).

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William L. Mengeling From the Virology Swine Research Unit, National Animal Disease Center, USDA, Agricultural Research Service P. O. Box 70, Ames, IA 50010 (Wesley, Mengeling, Lager, Vorwald), and Boehringer Ingelheim/NOBL Laboratories Inc 2501 N Loop Dr, Ames, IA 50010 (Roof).

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Kelly M. Lager From the Virology Swine Research Unit, National Animal Disease Center, USDA, Agricultural Research Service P. O. Box 70, Ames, IA 50010 (Wesley, Mengeling, Lager, Vorwald), and Boehringer Ingelheim/NOBL Laboratories Inc 2501 N Loop Dr, Ames, IA 50010 (Roof).

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Ann C. Vorwald From the Virology Swine Research Unit, National Animal Disease Center, USDA, Agricultural Research Service P. O. Box 70, Ames, IA 50010 (Wesley, Mengeling, Lager, Vorwald), and Boehringer Ingelheim/NOBL Laboratories Inc 2501 N Loop Dr, Ames, IA 50010 (Roof).

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Michael B. Roof From the Virology Swine Research Unit, National Animal Disease Center, USDA, Agricultural Research Service P. O. Box 70, Ames, IA 50010 (Wesley, Mengeling, Lager, Vorwald), and Boehringer Ingelheim/NOBL Laboratories Inc 2501 N Loop Dr, Ames, IA 50010 (Roof).

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Abstract

Objective

To determine stability of the restriction fragment length polymorphism (RFLP) pattern of a porcine reproductive and respiratory syndrome vaccine virus and patterns of other viral strains as they replicate in pigs.

Sample Population

Field samples of porcine reproductive and respiratory syndrome virus (PRRSV) and samples from 2 weaned pigs, 2 nursery-age pigs, and 5 gilts experimentally infected with PRRSV.

Procedure

PRRSV was isolated from field samples, experimentally infected pigs, or pigs that were in contact with experimentally infected pigs. For each virus, RNA was isolated from infected cells, and RFLP patterns were determined.

Results

61 % of field samples had 2-5-2 RFLP patterns characteristic of the vaccine virus, 32% had field virus RFLP patterns, and 7% had intermediate RFLP patterns that indicated a virus with a close relationship to the vaccine virus. Viruses isolated from experimentally infected pigs had no change in RFLP patterns after up to 13 weeks of in vivo replication and transmission to contact pigs.

Conclusions and Clinical Relevance

RFLP patterns distinguish the vaccine and field strains of PRRSV; however, as the vaccine virus spreads among a swine population, the RFLP pattern can change to a related intermediate pattern. A glycine at residue 151 of open reading frame 5 is another marker for the vaccine virus; this glycine is rapidly lost and eventually replaced with arginine as the vaccine virus replicates in pigs. (Am J Vet Res 1999;60:463-467)

Abstract

Objective

To determine stability of the restriction fragment length polymorphism (RFLP) pattern of a porcine reproductive and respiratory syndrome vaccine virus and patterns of other viral strains as they replicate in pigs.

Sample Population

Field samples of porcine reproductive and respiratory syndrome virus (PRRSV) and samples from 2 weaned pigs, 2 nursery-age pigs, and 5 gilts experimentally infected with PRRSV.

Procedure

PRRSV was isolated from field samples, experimentally infected pigs, or pigs that were in contact with experimentally infected pigs. For each virus, RNA was isolated from infected cells, and RFLP patterns were determined.

Results

61 % of field samples had 2-5-2 RFLP patterns characteristic of the vaccine virus, 32% had field virus RFLP patterns, and 7% had intermediate RFLP patterns that indicated a virus with a close relationship to the vaccine virus. Viruses isolated from experimentally infected pigs had no change in RFLP patterns after up to 13 weeks of in vivo replication and transmission to contact pigs.

Conclusions and Clinical Relevance

RFLP patterns distinguish the vaccine and field strains of PRRSV; however, as the vaccine virus spreads among a swine population, the RFLP pattern can change to a related intermediate pattern. A glycine at residue 151 of open reading frame 5 is another marker for the vaccine virus; this glycine is rapidly lost and eventually replaced with arginine as the vaccine virus replicates in pigs. (Am J Vet Res 1999;60:463-467)

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