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Biomedical subjects

W L Mengeling

Publications and source records attributed to W L Mengeling.

At least 37 records · Page 2Linked to original sources
PubMed1997

Homologous challenge of porcine reproductive and respiratory syndrome virus immunity in pregnant swine.

The clinical consequences of single or multiple exposure of pregnant gilts to porcine reproductive and respiratory syndrome virus (PRRSV) at various stages of gestation were determined. Thirty-three pregnant gilts were allotted to 6 experimental groups (5 to 7 gilts/group). Gilts of groups 1 to 5 were exposed to strain NADC-8 of PRRSV at the following times: group 1, gestation day (GD) 1; group 2, GDs 1 and 90; group 3, GD 30; group 4, GDs 30 and 90; group 5, GD 90. Virus exposure was by either intrauterine (GD 1) or oronasal (GDs 30 and 90) inoculation. Gilts of group 6 were kept as nonexposed controls. Gilts were either necropsied on or about GD 111 (groups 1 to 5) or were allowed to farrow (group 6). The detection of PRRSV in serum of fetuses and piglets (within 12 hof birth) was considered evidence of transplacental infection. Transplacental infection and virus-induced death were and were not confirmed for groups 3, 4, and 5 and for groups 1, 2, and 6, respectively. Collectively, the results indicated that intrauterine exposure to PRRSV at GD 1 was without clinical effect (groups 1 and 2) and provided protection against subsequent exposure to the same strain of virus at GD 90 (group 2). The highest incidence of transplacental infection and fetal death followed a single exposure to PRRSV at GD 90 (group 5).

Animals↗
PubMed1997

Vaccination with recombinant vaccinia virus vaccines expressing glycoprotein genes of pseudorabies virus in the presence of maternal immunity.

Piglets which had received colostral antibody to pseudorabie virus (PRV) were divided into four groups and inoculated with a NYVAC vaccinia recombinant expressing glycoprotein gD of PRV, a NYVAC recombinant expressing glycoprotein gB of PRV, an inactivated PRV vaccine, or no vaccine. The piglets were vaccinated twice, 3 weeks apart, beginning at approximately 2 weeks of age and later challenged with virulent PRV oronasally. All three vaccines protected similarly when no maternal antibody was present. Although all three vaccines induced some active immunity in piglets with maternal antibody, piglets receiving the NYVAC/gB vaccine were the only ones protected similarly whether or not they had maternal antibodies to PRV.

Animals↗
PubMed1996

Effect of post-coital intrauterine inoculation of porcine reproductive and respiratory syndrome virus on conception in gilts.

The effect of porcine reproductive and respiratory syndrome virus (PRRSV) on early gestation was investigated by exposing susceptible gilts to the virus shortly after they had been bred naturally. Sixteen gilts were exposed intrauterinely to PRRSV and 23 gilts received a sham inoculum. One day after exposure, and on or about seven, 14, and 30 days after exposure, the gilts were bled and the serum was tested for PRRSV and homologous antibody. The pregnancy status of each gilt was determined on day 30 by ultrasound, and near or at term either by necropsy or by allowing the gilts to farrow naturally. All 16 gilts exposed to PRRSV became infected, as evidenced by the detection of PRRSV in seven of the gilts and homologous antibody in the serum of all of them, whereas all the 23 gilts exposed to a sham inoculum remained free of both virus and antibody. Ten of the 16 infected gilts conceived, and 19 of the 23 uninfected gilts conceived, but the difference in conception rate was not statistically significant. Moreover, the mean numbers of live fetuses or pigs per litter of the infected and uninfected gilts were similar (9.7 and 9.3). These results suggest that the intrauterine infection of susceptible pigs with PRRSV at or near the time of conception may have little or no effect on their reproductive performance.

Animals↗
PubMed1996

Diagnosis of porcine reproductive and respiratory syndrome using infected alveolar macrophages collected from live pigs.

A highly sensitive method of detecting infection of live pigs with porcine reproductive and respiratory syndrome virus (PRRSV) was developed by testing alveolar macrophages collected by pulmonary lavage. Five pigs were exposed by oronasal inoculation or by contact to PRRSV when they were 10 (1 pig) or 14 weeks (4 pigs) of age. Diagnostic samples (alveolar macrophages and sera) were collected from each pig just before exposure to PRRSV. During the next 9 weeks sera were collected at weekly intervals and alveolar macrophages were collected at weeks 2 and 4-9. Both sera and alveolar macrophages were suitable for detecting early infection, but alveolar macrophages were clearly the better sample after longer intervals. Virus was last isolated from serum at week 4 (from 1 of 5 pigs), whereas it was isolated from the alveolar macrophages of 4 of the 5 pigs at week 4 and from at least 2 pigs at each of the weekly intervals thereafter (i.e. weeks 5, 6, 7, 8, and 9 postexposure). The most sensitive method of testing alveolar macrophages for PRRSV was cocultivation with MARC-145 cells. None of the pigs had any clinical signs after exposure to PRRSV or as a result of pulmonary lavage and there was no evidence that repeated pulmonary lavage caused anything other than a mild, transient (mild hyperemia) tissue reaction.

Animals↗
PubMed1996

Comparison among strains of porcine reproductive and respiratory syndrome virus for their ability to cause reproductive failure.

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.

Animals↗
PubMed1995

Diagnosis of porcine reproductive and respiratory syndrome.

The most suitable tissue samples and test procedures for the etiologic diagnosis of porcine reproductive and respiratory syndrome (PRRS) were found to depend on several variables including the age of the pig from which tissues were collected, the stage of infection (acute or persistent), the available complement of diagnostic reagents, and the urgency in obtaining results. When the diagnosis involved acute infection of congenitally or neonatally infected pigs, and susceptible cell culture(s) was available for virus isolation, then both serum and alveolar macrophages (AM) were reliable samples. Alveolar macrophages flushed from infected lungs provided a temporal advantage, however, in that in addition to their use for virus isolation, i.e., from a lysate of AM, they could be cultured in vitro and examined for the presence of viral antigens by immunofluorescence microscopy (FA) as early as 1 hour after they were added to the culture vessel. The examination of AM in this manner also circumvented the need for additional cell cultures to test for infectious virus. Testing presuckling sera by indirect FA for antibodies to PRRS virus also was of diagnostic value and, like FA with AM, could be completed soon after sample collection. For older pigs, AM were more reliable than serum, lungs, or any of 27 other tissues evaluated as diagnostic samples and were often the only samples in which infectious virus and viral antigens were detected when pigs were euthanized more than 3 weeks postexposure. A simple procedure for on-farm collection of AM as well as methods for testing AM for viral antigens and neonatal (presuckling) sera for homologous antibody in a modestly equipped laboratory, such as one that might be maintained by a veterinary practitioner, are described and discussed.

Animals↗
PubMed1995

Pathogenesis of in utero infection in porcine fetuses with porcine reproductive and respiratory syndrome virus.

Porcine fetuses were exposed in utero to porcine reproductive and respiratory syndrome virus (PRRSV) at stages of gestation ranging from 34 to 85 days and examined 17 to 31 days later to determine the effect of gestational age on fetal susceptibility. For each of the 8 litters tested during the study, all of the fetuses of 1 horn of the uterus were exposed to virus by intraamniotic injection; those of the other horn were exposed similarly to a sham inoculum that consisted of sterile cell culture medium. Viral infectivity titers associated with fetal tissues collected at necropsy indicated that, regardless of gestational age, the virus had replicated in fetuses exposed intraamniotically. In addition, virus had also spread and replicated in sham-inoculated littermates in 3 litters. On the basis of these findings it appears that there may be little or no temporal difference in fetal susceptibility to infection with PRRSV. If so, the lack of early fetal death as a commonly recognized feature of naturally occurring cases of PRRS may be due to a greater resistance of early gestational fetuses to the lethal effects of PRRSV, as suggested by this study, and/or a greater likelihood of transplacental infection during late gestation.

Animals↗
PubMed1994

Evaluation of a recombinant vaccinia virus containing pseudorabies (PR) virus glycoprotein genes gp50, gII, and gIII as a PR vaccine for pigs.

Pigs vaccinated twice intramuscularly with a highly attenuated strain of vaccinia virus (NYVAC) containing gene inserts for pseudorabies virus (PRV) glycoproteins gp50, gII, and gIII produced neutralizing antibodies for PRV and were less clinically affected than were nonvaccinated pigs following oronasal exposure to virulent PRV. Also, following oronasal exposure to virulent PRV the duration of virulent virus shedding by pigs that had been vaccinated intramuscularly with the recombinant virus was statistically less (p < 0.05) than that of nonvaccinated pigs and like that of pigs vaccinated twice intramuscularly with inactivated PR vaccine. Intramuscular vaccination with the recombinant virus was compatible with the most commonly used differential diagnostic tests, namely those based on PRV glycoproteins gX and gI. Serum antibodies for these glycoproteins were absent from the sera of all pigs before and after vaccination with recombinant virus; whereas, they were present in the sera of all of the same pigs after they were exposed to virulent PRV. In contrast to the effectiveness of the recombinant virus administered intramuscularly, neither serum antibody nor clinical protection against PRV was detected when aliquots of the same recombinant virus preparation were administered either orally or intranasally. The latter finding suggests that recombinant virus replicates poorly, if at all, at these sites. If so, the dissemination of recombinant virus from vaccinated pigs to nonvaccinated pigs or other animals in contact seems unlikely.

Animals↗
PubMed1994

Early interaction of feline calicivirus with cells in culture.

The kinetics and biochemical properties of feline calicivirus (FCV) attachment to Crandell-Reese feline kidney cells were determined. Maximum binding was observed at pH 6.5. Cells in suspension at 4 degrees C bound virus more efficiently than cells in monolayers at 4 degrees C or 37 degrees C. High initial binding rate was observed in monolayers or cells in suspension and proceeded to a maximum at 90 min, although half maximal binding was observed as early as 15 min. Binding was specific and competitively blocked by serotypically homologous or heterologous FCV as well as by San Miguel sea lion virus. Treatment of cells with proteases increased FCV binding, whereas phospholipase had no effect on virus attachment. Conversely, cells treated with neuraminidase followed by O-glycanase treatment showed a decreased binding ability. Cells of feline origin bound FCV very efficiently, and non-permissive cells showed a poor binding ability. Following transfection of viral RNA, infectious virus could be recovered from all non-permissive cells, except from Madin-Darby canine kidney cells. These results suggest that FCV binds to a receptor in which carbohydrates may be an important component and that FCV replication in non-permissive cells is primarily restricted by the absence of appropriate receptors on the cell surface.

Animals↗
PubMed1994

Temporal characterization of transplacental infection of porcine fetuses with porcine reproductive and respiratory syndrome virus.

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 PRRSV at 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 PRRSV and 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 (chi 2 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, PRRSV was 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.

Animals↗
PubMed1993

Genomic cloning and restriction site mapping of a porcine adenovirus isolate: demonstration of genomic stability in porcine adenovirus.

Restriction endonuclease maps were constructed for the genome of a porcine adenovirus (PAV), NADC-1, which was isolated in 1972 from an adult swine. Genomic DNA libraries of NADC-1 Bam HI, Eco RI/Bam HI, and Sph I fragments were cloned into pUC-18. Using the cloned NADC-1 Bam HI and Eco RI/Bam HI fragments as probes, Southern blot hybridizations were performed to human adenovirus 2 (Ad-2) restriction fragments to determine the left-to-right orientation of the Bam HI and Eco RI/Bam HI fragments. Genomic NADC-1 DNA was cleaved with ten restriction endonucleases (RE). Using cloned NADC-1 genomic fragments as probes in Southern blot hybridizations, an RE site map was constructed. Nucleotide sequencing of four clones confirmed several RE sites. The size of the NADC-1 genome was determined to be approximately 32 kbp. The size of Hind III, Xba I, Sma I, Eco RI, Bam HI, Bgl II, Pst I, and Sph I RE fragments from NADC-1 was compared to those from the reference strain of PAV serotype 4 (F618), and to two recent isolates, NADC-2 and NADC-3. For all restriction enzymes examined, the sizes of the NADC-1 fragments were identical to PAV-4, NADC-2, and NADC-3 fragments, indicating that the NADC-1 isolate is very closely related, if not identical, to PAV-4 and two recent isolates. Southern blot hybridizations also indicated that NADC-1, NADC-2, NADC-3, and PAV-4 are very similar and revealed regions of sequence similarity between NADC-1 and human Ad-2 and human Ad-5.

Adenoviridae↗
PubMed1993

Vaccination of pigs against pseudorabies with highly attenuated vaccinia (NYVAC) recombinant viruses.

Poxvirus recombinants, based on the highly attenuated NYVAC strain of vaccinia virus (Tartaglia et al., 1992), containing single gene inserts encoding the pseudorabies virus (PRV) gII, gIII, or gp50 glycoproteins were tested for their immunogenicity in pigs. Twenty-four pigs were randomly divided into six groups of four. Groups 1-3 were inoculated with 10(7) CCID50 of NYVAC/PRV gII, NYVAC/PRV gIII, or NYVAC/PRV gp50, respectively, while groups 4 and 5 received the NYVAC parent virus or an inactivated PRV vaccine control, respectively. Group 6 represented the sham vaccinated control group. All inoculations were given by the intramuscular route on weeks 0 and 4. The candidate vaccines were shown to be safe with no local or systemic reactions. At 4 weeks following the second inoculation, all pigs were challenged by an oronasal administration of a virulent PRV strain. Pigs were monitored before and after challenge for clinical manifestations resulting from vaccination and challenge exposure, respectively. Sera were analyzed for PRV neutralizing activity. Virological analyses after challenge included assessment of virus shedding and the development of latent PRV infections. All but one animal developed latent PRV infection following challenge exposure; however, significant protection against PRV-induced signs was afforded by vaccination with either the NYVAC/PRV gp50 or NYVAC/PRV gII recombinant viruses, as well as with the inactivated PRV vaccine. The NYVAC/PRV gp50 also reduced overall virus shedding after challenge. The extent of protection against PRV-induced clinical signs, in general, was associated with the level of pre-challenge virus neutralizing activity.

Animals↗
PubMed1993

Analysis of feline calicivirus capsid protein genes: identification of variable antigenic determinant regions of the protein.

Three isolates of feline calicivirus (FCV) designated NADC, KCD and CFI/68 were compared for biochemical, serological and genetic variation within the capsid protein gene. The M(r) of the capsid protein from purified virions was approximately 66,000 for the NADC virus isolate, which differed slightly from the relative mobilities of the purified capsid proteins of the KCD and CFI/68 isolates. Polyclonal antisera from either cats infected or rabbits hyperimmunized with the CFI/68 isolate cross-reacted with all three isolates by Western blot analysis. However, these polyclonal antisera to CFI/68 varied considerably in their virus-neutralization titres to the KCD and NADC isolates. Nucleotide sequence data confirmed the genetic variability among these FCV isolates. Comparison of the predicted amino acid sequence of the capsid protein among isolates revealed two regions of sequence divergence that probably contain the antigenically variable determinants. These hypervariable regions may vary by as much as 55% among isolates of FCV. The amino acid sequence diversity in the hypervariable regions of the KCD and NADC isolates correlated well with the virus-neutralization data and suggests that polyvalent vaccines may be more protective than the commonly used monovalent vaccines.

Amino Acid Sequence↗