Transmission of two pseudorabies virus strains that differ in virulence and virus excretion in groups of vaccinated pigs

A. Bouma From the DLO-Institute for Animal Science and Health, PO Box 365, 8200 AJ, Lelystad (Bouma, De Jong, Kimman), and Department of Herd Health and Reproduction, University of Utrecht, Utrecht (Bouma), The Netherlands.

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M. C. M. De Jong From the DLO-Institute for Animal Science and Health, PO Box 365, 8200 AJ, Lelystad (Bouma, De Jong, Kimman), and Department of Herd Health and Reproduction, University of Utrecht, Utrecht (Bouma), The Netherlands.

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T. G. Kimman From the DLO-Institute for Animal Science and Health, PO Box 365, 8200 AJ, Lelystad (Bouma, De Jong, Kimman), and Department of Herd Health and Reproduction, University of Utrecht, Utrecht (Bouma), The Netherlands.

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Abstract

Objective

To determine whether 2 Pseudorabies virus (PRV) strains that differ in virulence differ in transmission among vaccine strain 783-inoculated pigs.

Design

Three experiments were conducted, each with 2 groups of 10 pigs inoculated with the glycoprotein E-negative vaccine 783. In the first 2 experiments, half of one group was inoculated with the mildly virulent strain Sterksel, and half of the other group was inoculated with the virulent strain NIA-3. The remaining pigs were contact-exposed to the inoculated pigs. In the third experiment, 2 pigs in each group were inoculated with strain NIA-3, and the other 8 pigs in each group were contact-exposed to these 2 pigs.

Animals

Specific-pathogen-free pigs that were seronegative for antibodies to PRV.

Procedure

Estimation of the transmission of virus in each group was based on a stochastic model, in which the observable variable was the number of contact infections. The sole parameter of the model was the reproduction ratio θ. A glycoprotein E ELISA was used to determine whether infection occurred. Virus excretion in the oropharyngeal fluid was determined by plaque assay to measure infectivity.

Results

Vaccinated pigs had a significant difference in virus excretion between the mildly virulent and virulent strains. Sterksel strain-inoculated pigs shed significantly more virus than did NIA-3 strain-inoculated pigs. Despite this difference in virus excretion, the 2 strains did not differ in transmission.

Conclusions

Both PRV strains would be eliminated from a population of vaccine strain 783-inoculated pigs. (Am J Vet Res 1996;57:43-47)

Abstract

Objective

To determine whether 2 Pseudorabies virus (PRV) strains that differ in virulence differ in transmission among vaccine strain 783-inoculated pigs.

Design

Three experiments were conducted, each with 2 groups of 10 pigs inoculated with the glycoprotein E-negative vaccine 783. In the first 2 experiments, half of one group was inoculated with the mildly virulent strain Sterksel, and half of the other group was inoculated with the virulent strain NIA-3. The remaining pigs were contact-exposed to the inoculated pigs. In the third experiment, 2 pigs in each group were inoculated with strain NIA-3, and the other 8 pigs in each group were contact-exposed to these 2 pigs.

Animals

Specific-pathogen-free pigs that were seronegative for antibodies to PRV.

Procedure

Estimation of the transmission of virus in each group was based on a stochastic model, in which the observable variable was the number of contact infections. The sole parameter of the model was the reproduction ratio θ. A glycoprotein E ELISA was used to determine whether infection occurred. Virus excretion in the oropharyngeal fluid was determined by plaque assay to measure infectivity.

Results

Vaccinated pigs had a significant difference in virus excretion between the mildly virulent and virulent strains. Sterksel strain-inoculated pigs shed significantly more virus than did NIA-3 strain-inoculated pigs. Despite this difference in virus excretion, the 2 strains did not differ in transmission.

Conclusions

Both PRV strains would be eliminated from a population of vaccine strain 783-inoculated pigs. (Am J Vet Res 1996;57:43-47)

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