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  • Author or Editor: Ronald D. Wesley x
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Abstract

Objective

To test the ability of porcine respiratory coronavirus (PRCV) to induce protective immunity to antigenically related transmissible gastroenteritis virus (TGEV) in neonatal pigs.

Design

Neonatal pigs were exposed to PRCV when they were 2, 4, or 6 days old and challenge-exposed to virulent TGEV at 10 days of age.

Animals

34 hysterectomy-derived, colostrum-deprived pigs.

Procedure

After challenge exposure, clinical signs were observed, body weight, antibody response, and virus shedding were measured, and mortality was determined.

Results

After exposure to PRCV, principals had a slightly slower rate of weight gain than did controls; with 1 exception (a PRCV-exposed pig that was dyspneic for 1 day), principals and controls remained clinically normal until shortly after challenge exposure, when all pigs became listless and anorectic and developed watery diarrhea. However, by day 3, most of the pigs that had been exposed to PRCV when they were either 2 or 4 days old began to recover and most (15/18) survived. Conversely, the clinical condition of most of the other pigs worsened and most (14/16) died. Pigs exposed to PRCV when they were 2 or 4 days old also differed from all other pigs in that they had serum virus-neutralizing antibodies for PRCV and TGEV at the time of challenge exposure.

Conclusions

The PRCV can induce protective immunity to TGEV in neonatal pigs and such immunity develops at or about 6 days after exposure to PRCV. Moreover, protective immunity may be coincident with the appearance of virus-neutralizing antibody.

Clinical Relevance

Exposure to PRCV should enhance a TGE herd vaccination program.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate the safety and efficacy of a human adenovirus-5 vaccine for protecting weaned pigs against swine influenza virus subtype H3N2 infection when administered via 2 injection methods.

Animals—76 pigs.

Procedure—6 groups of weaned pigs received a 10- fold serial dilution of recombinant adenovirus expressing H3 hemagglutinin and a constant amount of recombinant adenovirus expressing nucleoprotein, either via a needle-free injection device or by traditional IM injection. In each group of 10 pigs, 1 served as a nonvaccinated contact pig to monitor whether there was spread of vaccinial virus from pig to pig. Vaccinated pigs and nonvaccinated controls were challenged or sham-inoculated 5 weeks later. After challenge, pigs were observed for clinical signs and nasal secretions were tested for virus. On day 5 after challenge, pigs were euthanatized; lungs were examined for gross lesions, and bronchoalveolar lavage specimens were tested for virus replication.

Results—A hemagglutination inhibition (HI) antibody response was elicited in a dose-dependent manner. Traditional IM administered vaccination induced consistently higher HI antibody responses than vaccination via needle-free injection, but the differences were not significant. Likewise, traditional IM administration was superior at reducing nasal virus shedding except at the highest dose, at which both methods blocked virus replication. The severity of lung lesions was reduced in a dose-dependent manner by both vaccination methods. Sentinel pigs did not seroconvert.

Conclusions and Clinical Relevance—The human adenovirus-5 vaccine at high doses prevented nasal virus shedding after challenge exposure with both methods of administration. The replication-defective vaccine virus was not transmitted to sentinel pigs. (Am J Vet Res 2005;66:1943–1947)

Full access
in American Journal of Veterinary Research

Summary

A recombinant pseudorabies virus that is defective in the early protein 0 (EP0) and large latency transcript (LLT) genes was constructed. A portion of the EP0 and LLT genes was replaced by the lacZ gene of Escherichia coli that had been placed under the control of the pseudorabies virus gX gene promoter. This recombinant virus produces smaller size plaques and yields less virus than does the parent virus on Madin-Darby bovine kidney cells. Although the time course of virus replication and release into the medium of the recombinant and parent viruses are similar, the recombinant virus did not reach as high a titer. Similar to the parent virus, the recombinant virus replicates in the upper segment of the respiratory tract of swine, but the amount of progeny viruses produced is significantly reduced. The data indicated that the EP0 and LLT genes of pseudorabies virus are nonessential for replication. Virus that lacks these 2 genes has impaired growth in tissue culture and is attenuated for swine, compared with the parent virus.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine the predominant strain of progeny virus in samples obtained from cell cultures and pigs exposed simultaneously to attenuated and virulent strains of porcine reproductive and respiratory syndrome virus (PRRSV).

Sample population

Cell cultures and twenty 4-week-old pigs.

Procedure

Cell cultures and pigs were simultaneously exposed to various relative concentrations of an attenuated, cell-culture-adapted vaccine strain and a virulent field strain of PRRSV. Progeny virus obtained at selected intervals thereafter was tested to determine strain identity by use of restriction fragment length polymorphism (RFLP) analysis.

Results

Progeny virus from infected cell cultures comprised the attenuated strain, alone or in combination with the virulent strain, except when cultures had been exposed to a large excess (> 100,000-fold) of the virulent strain. Progeny virus from infected pigs comprised only the virulent strain regardless of the relative concentrations of the 2 strains to which the pigs had been exposed.

Conclusions

During concurrent replication in cell cultures, the attenuated strain quickly predominated. Conversely, during concurrent replication in pigs, the virulent strain quickly predominated.

Clinical Relevance

It is unlikely that only an attenuated strain of PRRSV would be identified by RFLP testing of samples obtained from pigs concurrently infected with a virulent strain of PRRSV. Nevertheless, the ability of a cell-culture-adapted attenuated strain of PRRSV to predominate during cell culture passage (the first step in the current RFLP testing procedure) indicated that, if possible, samples should be obtained from pigs that do not have a history of direct or indirect exposure to attenuated-virus vaccine. (Am J Vet Res 1999;60:119–122)

Free access
in American Journal of Veterinary Research

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)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine the origin and clinical relevance of selected strains of porcine reproductive and respiratory syndrome (PARS) virus (PRRSV).

Animals

38 pigs without antibodies for PRRSV.

Procedure

A seemingly uncommon restriction endonuclease digestion site in a commercially available vaccine strain of attenuated PRRSV was tested for its stability and prevalence under defined conditions. Selected field strains of PRRSV, with or without the restriction-site marker, were subsequently tested in pigs for virulence and for their ability to replicate competitively in pigs simultaneously given the vaccine.

Results

Under experimental conditions, the restriction-site marker was stable during long-term infection of pigs. It was not detected in any of the 25 field strains of PRRSV that were isolated before use of the vaccine or 21 of 25 field strains that were isolated after use of the vaccine but that, on the basis of previous testing, were believed unrelated to the vaccine strain. Conversely, it was detected in 24 of 25 field strains that were isolated after use of the vaccine and that, on the basis of previous testing, were believed to be direct-line descendants of the vaccine strain. Putative vaccine-related strains caused more pronounced pathologic changes than did the vaccine strain alone, and they predominated during replication in pigs also given the vaccine strain.

Conclusions

In some swine herds, the vaccine strain may have persisted and mutated to a less attenuated form.

Clinical Relevance

The potential for persistence and mutation of specific strains of virus should be an important consideration when designing vaccination programs involving attenuated PRRSV. (Am J Vet Res 1999;60:334–340)

Free access
in American Journal of Veterinary Research