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  • Author or Editor: Kelly M. Lager x
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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

Objective

To determine the effect of congenital and early postnatal infection of pigs with porcine reproductive and respiratory syndrome virus (PRRSV) on postnatal survival and growth.

Animals

20 pregnant gilts and their pigs and fetuses.

Procedure

16 pregnant gilts (principals) comprising 4 groups (4 gilts/group) were exposed oronasally to 4 strains of PRRSV (a vaccine strain, and 3 field strains) at or about day 90 of gestation. Four pregnant gilts (controls) were kept under similar conditions, except for exposure to PRRSV. Samples collected from pigs before ingestion of colostrum and samples and specimens collected from pigs at selected times thereafter were tested for PRRSV and homologous antibody. Pigs were observed for clinical signs and were weighed at birth and at weekly intervals until they were euthanatized and necropsied at about 3 weeks of age.

Results

At least some members of all litters of principal gilts were infected congenitally. Most noninfected, liveborn littermates became infected within the first week of life. Infection of pigs with field strains did, and infection of pigs with the vaccine strain did not, adversely affect postnatal survival and growth rate. All infected pigs had generalized lymph node enlargement.

Conclusion

Exposure of pregnant gilts to either attenuated (vaccine) or virulent (field) strains of PRRSV can result in congenital infection. Vaccine as well as field strains can be transmitted postnatally from infected to noninfected littermates. Pigs infected with field strains have a poorer rate of survival and growth than do noninfected pigs.

Clinical Relevance

Because attenuated (vaccine) PRRSV can cause congenital infection and be transmitted postnatally from congenitally infected to immune-naive pigs, the use of attenuated virus during gestation is, at best, questionable. (Am J Vet Res 1998;59:52–55)

Free access
in American Journal of Veterinary Research

Summary

Pregnant gilts were exposed to porcine reproductive and respiratory syndrome virus (prrsv ) by iv inoculation at or about gestation day 30 (3 gilts), 50 (3 gilts), 70 (3 gilts), or 90 (5 gilts) to investigate the likelihood of transplacental infection with prrsvat various stages of gestation. At or about 3, 6, and 9 weeks after exposure, gilts were either euthanatized while still pregnant or allowed to farrow. Gilts and pigs were observed for clinical signs of infection, and gilts, pigs, and fetuses were tested for prrsvand homologous antibody. All gilts were healthy throughout the study, except that farrowing was sometimes difficult and prolonged, and 2 gilts failed to farrow the entire litter. One gilt farrowed on day 111 of gestation; all others farrowed on day 114 or later. Porcine reproductive and respiratory virus was isolated from significantly (x2 test, P < 0.01) more fetuses and live and stillborn pigs of the 5 gilts that were infected at 90 or 92 days of gestation than from the fetuses and live and stillborn pigs of the 9 gilts that were infected at 72 or fewer days of gestation (ie, 33 of 44, 75% vs 3 of 78,4%). After initial infection, prrsvwas isolated from gilts and their pigs for a maximum of 3 weeks and 8 to 11 weeks, respectively. Findings of this study, with regard to the temporal aspects of transplacental infection, may help explain why natural epizootics of prrsv-induced maternal reproductive failure are often recognized principally as problems of late-term gestation and neonatal survival.

Free access
in American Journal of Veterinary Research

Summary

Various procedures of vaccination for Pseudorabies were compared for their effects on shedding, latency, and reactivation of attenuated and virulent Pseudorabies virus. The study included 6 groups: group 1 (10 swine neither vaccinated nor challenge-exposed), group 2 (20 swine not vaccinated, but challenge-exposed), and groups 3 through 6 (10 swine/group, all vaccinated and challenge-exposed). Swine were vaccinated with killed virus im (group 3) or intranasally (group 4), or with live virus im (group 5) or intranasally (group 6). The chronologic order of treatments was as follows: vaccination (week 0), challenge of immunity by oronasal exposure to virulent virus (week 4), biopsy of tonsillar tissue (week 12), treatment with dexamethasone in an attempt to reactivate latent virus (week 15), and necropsy (week 21).

Vaccination im with killed or live virus and vaccination intranasally with live virus mitigated clinical signs and markedly reduced the magnitude and duration of virus shedding after challenge exposure. Abatement of signs and shedding was most pronounced for swine that had been vaccinated intranasally with live virus. All swine, except 4 from group 2 and 1 from group 4, survived challenge exposure. Only vaccination intranasally with live virus was effective in reducing the magnitude and duration of virus shedding after virus reactivation. Vaccination intranasally with killed virus was without measurable effect on immunity.

Of the 55 swine that survived challenge exposure, 54 were shown subsequently to have latent infections by use of dexamethasone-induced virus reactivation, and 53 were shown to have latent infections by use of polymerase chain reaction (pcr) with trigeminal ganglia specimens collected at necropsy. Fewer swine were identified by pcr as having latent infections when other tissues were examined; 20 were identified by testing specimens of olfactory bulbs, 4 by testing tonsil specimens collected at necropsy, and 4 by testing tonsillar biopsy specimens. Eighteen of the 20 specimens of olfactory bulbs and 3 of the 4 tonsil specimens collected at necropsy in which virus was detected by pcr were from swine without detectable virus-neutralizing antibody at the time of challenge exposure. One pig that had been vaccinated intranasally with live virus shed vaccine virus from the nose and virulent virus from the pharynx concurrently after dexamethasone treatment. Evaluation of both viral populations for unique strain characteristics failed to provide evidence of virus recombination.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine clinical consequences of exposing pregnant gilts to strains of porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) isolated from field cases of “atypical” or “acute” PRRS in vaccinated herds.

Animals

20 pregnant gilts and their pigs and fetuses.

Procedure

8 pregnant gilts (principals: 4 groups [2 gilts/group]) were exposed oronasally at or about 45 days of gestation to 1 of 4 strains of PRRSV and necropsied 6 weeks later. Nonexposed controls (2 additional pregnant gilts) were kept under otherwise similar conditions. The experiment was repeated, except that principals were exposed at or approximately 90 days of gestation and allowed to farrow. Clinical observations were made at least twice daily, and samples and specimens from gilts and their fetuses and pigs were tested for PRRSV and homologous antibody.

Results

Exposure of pregnant gilts to PRRSV at or approximately 45 days' gestation resulted in low prevalence of transplacental infection and fetal death. Exposure of pregnant gilts to PRRSV at or approximately 90 days' gestation resulted in higher prevalence of transplacental infection and fetal death. Moreover, 1 gilt aborted and many liveborn pigs of other litters were weak and unthrifty. Clinical signs of disease and reproductive failure were especially severe for a field strain of PRRSV isolated from an epizootic that fit the strictest definition of atypical PRRS. Controls remained clinically normal and free of PRRSV.

Conclusion and Clinical Relevance

Some strains of PRRSV now circulating in US swine herds are more virulent than those encountered in the past. Clinical PRRS in vaccinated herds suggests need for a new generation of vaccines. (Am J Vet Res 1998;59:1540-1544)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To compare the virulence of selected strains of porcine reproductive and respiratory syndrome virus (PRRSV) relative to reproductive performance of pregnant gilts.

Design

16 pregnant gilts (principals) were exposed oronasally to 4 strains (vaccine strain RespPRRS, field strains VR-2385, VR-2431, and NADC-8, 4 gilts/strain) of PRRSV on or about day 90 of gestation. 4 pregnant gilts (controls) were kept under similar conditions, except for exposure to PRRSV. Samples and specimens obtained from gilts, pigs (before ingestion of colostrum), and fetuses were tested for PRRSV and homologous antibody.

Animals

20 pregnant gilts.

Procedure

The virulence of each strain of PRRSV was evaluated mainly on the clinical status of the corresponding litters at farrowing.

Results

Most gilts remained clinically normal throughout the study and farrowed normally at or near the expected farrowing time. All virus strains crossed the placenta of principal gilts to infect fetuses in utero. The number of late-term dead fetuses (which appeared to be the best measure of relative virulence) ranged from 0 for litters of control gilts and gilts exposed to strain RespPRRS, to 38 for gilts exposed to strain NADC-8. All principal gilts became viremic and developed antibody against PRRSV. All strains persisted in alveolar macrophages of at least some principal gilts for at least 7 weeks after exposure.

Conclusion

Strains of PRRSV vary in virulence.

Clinical Relevance

The effects of PRRSV on reproductive performance are strain dependent and this should be considered in making a tentative diagnosis on the basis of clinical observations. (Am J Vet Res 1996;57:834–839)

Free access
in American Journal of Veterinary Research

Abstract

Objectives

To determine whether intrauterine inoculation of porcine reproductive and respiratory syndrome virus (PRRSV) interferes with conception and whether exposure to one strain of PRRSV provides protection against challenge-exposure (CE) with homologous or heterologous strains of PRRSV.

Animals

40 gilts.

Procedure

Gilts were inoculated by intrauterine administration of a PRRSV isolate (nadc-8) at breeding. Inoculated and noninoculated gilts were exposed oronasally to homologous (nadc-8) or heterologous (European isolate) PRRSV during late gestation. Specimens from gilts and fetuses were tested against CE virus. Lack of virus in gilts indicated protective immunity for the dam, in fetuses indicated protection of gilt from reproductive losses, and in both groups indicated complete protection.

Results

In the homologous CE group, interval from inoculation to CE ranged from 90 to 205 days, and protection was complete. In the heterologous CE group, interval from inoculation to CE ranged from 90 to 170 days, and protection was incomplete. The CE virus was detected in gilts necropsied 134 to 170 days after CE and in a litter necropsied 170 days after CE.

Conclusions

Homologous protection can be induced in gilts by exposure to live PRRSV. Heterologous protection from reproductive losses can be induced in gilts by exposure to live PRRSV; however, this protection is incomplete and may have a shorter duration than homologous protection.

Clinical Relevance

Exposure of swine to enzootic PRRSV will provide protection against homologous PRRSV-induced reproductive losses. Extent and duration of protection against heterologous PRRSV may be variable and dependent on antigenic relatedness of the virus strains used for inoculation and CE. (Am J Vet Res 1999;60:1022-1027)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine the safety and efficacy of vaccination of pregnant gilts with an attenuated strain of porcine reproductive and respiratory syndrome virus (PRRSV).

Animals

16 pregnant gilts.

Procedure

Pregnant gilts free of antibodies for PRRSV were assigned (4 gilts/group) to the following groups: group I, untreated controls; group II, vaccinated on day 60 of gestation; group III, vaccinated on day 60 of gestation and exposed to virulent PRRSV on day 90 of gestation; and group IV, exposed to virulent PRRSV on day 90 of gestation. Safety and efficacy of vaccination was evaluated by group comparisons of prenatal and postnatal survival of fetuses and pigs, respectively, and by the condition and rate of weight gain of liveborn pigs.

Results

Collective (prenatal and postnatal) death losses up to day 15 after farrowing (conclusion of study) were similar for groups I (7/47, 14.9%) and II (7/44, 16.9%) but were greater for group III (18/49, 36.7%) and were greater still for group IV (23/37, 62.2%). Mean body weight 15 days after farrowing was greatest for pigs in litters of group I (4.46 kg) and progressively less for the other groups (3.87, 3.76, and 2.18 kg for groups II, III, and IV, respectively).

Conclusions

Using these conditions, vaccination of gilts during midgestation appeared to be safe. However, it provided only partial protection against subsequent exposure to virulent virus.

Clinical Relevance

Attenuated-PRRSV vaccines may have to be administered to naive gilts > 30 days before conception to provide maximum protection throughout gestation. (Am J Vet Res 1999;60: 796–801)

Free access
in American Journal of Veterinary Research

The following article, “Virus-induced maternal reproductive failure of swine,” was prepared by Dr. Mengeling and his colleagues in response to our request that he provide a concise overview of some of what is presently known about this subject, especially in regard to events of the past 10 years. A lot has happened during this interval. For example, about a decade ago, the JAVMA published a report titled, “Farm studies of porcine parvovirus injection” (JAVMA, Mar15, 1983, pp 592–594). On the basis of this and other information available at the time, it was clear that porcine parvovirus (ppv) was an important reproductive pathogen for swine; however, the development of a vaccine for ppv-induced reproductive failure just a few years before suggested that the clinical impact of ppv soon would be minimized. It appears that this expectation has been realized, at least in part. What was not, and could not be, predicted, however, was that a new virus with devastating effects on swine reproduction would suddenly appear to counterbalance some of the gains made in the control of ppv. The new virus, now called porcine reproductive and respiratory syndrome virus, is currently prevalent throughout the major swine-producing areas of this country. In their article, Drs. Mengeling, Paul, and Lager focus mainly on the viruses, including porcine reproductive and respiratory syndrome virus, that are most often associated with maternal reproductive failure in swine in the United States, with special emphasis on information regarding control and diagnosis that would be of value to veterinarians in clinical practice.

Free access
in Journal of the American Veterinary Medical Association

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