Fermentation products as feed additives mitigate some ill-effects of heat stress in pigs.

Heat stress (HS) may result in economic losses to pig producers across the USA and worldwide. Despite significant advancements in management practices, HS continues to be a challenge. In this study, an in-feed antibiotic (carbadox, CBX) and antibiotic alternatives ( [XPC], and [SGX] fermentation products) were evaluated in a standard pig starter diet as mitigations against the negative effects of HS in pigs. A total of 100 gilts were obtained at weaning (6.87 ± 0.82 kg BW, 19.36 ± 0.72 d of age) and randomly assigned to dietary treatments (2 rooms/treatment, 2 pens/room, 6 to 7 pigs/pen). After 4 wk of dietary acclimation, half of the pigs in each dietary group (1 room/dietary treatment) were exposed to repeated heat stress conditions (RHS; daily cycles of 19 h at 25°C and 5 h at 40°C, repeated for 9 d), and the remaining pigs were housed at constant thermal neutral temperature (25°C, [NHS]). Pigs subjected to RHS had elevated skin surface temperature ( < 0.05; average 41.7°C) and respiration rate ( < 0.05; 199 breaths per minute (bpm) during HS, and overall reduced ( < 0.05) BW, ADG, ADFI, and G:F regardless of dietary treatment. Independent of diet, RHS pigs had significantly shorter ( < 0.05) jejunum villi on d 3 and d 9 compared to NHS pigs. Heat stress resulted in decreased villus height to crypt depth ratio (V:C) in pigs fed with control diet with no added feed additive (NON) and CBX diets at d 3, whereas the pigs fed diets containing XPC or SGX showed no decrease. Transcriptional expression of genes involved in cellular stress (, , , ), tight junction integrity (, , ), and immune response (, , and ) were measured in the ileum mucosa. Pigs in all dietary treatments subjected to RHS had significantly higher ( < 0.05) transcript levels of and , and an upward trend ( < 0.07) of mRNA expression. RHS pigs had higher ( < 0.05) transcript levels of and in NON diet, in XPC and CBX diets, and in SGX diet compared to the respective diet-matched pigs in the NHS conditions. Neither RHS nor diet affected peripheral natural killer () cell numbers or NK cell lytic activity. In conclusion, pigs subjected to RHS had decreased performance, and supplementation with fermentation products in the feed (XPC and SGX) protected pigs from injury to the jejunum mucosa.

Adenovirus-mediated expression of interferon-alpha delays viral replication and reduces disease signs in swine challenged with porcine reproductive and respiratory syndrome virus.

In this study, pigs were injected with a nonreplicating human adenovirus type 5 vector expressing porcine interferon-alpha (Ad5-pIFN-alpha) and then challenged with porcine reproductive and respiratory syndrome virus (PRRSV) to determine whether the presence of increased levels of IFN-alpha would decrease viral replication and/or disease. Groups of 10 pigs each were inoculated with Ad5-pIFN-alpha and not challenged, Ad5-pIFN-alpha and challenged with PRRSV 1 d later, or inoculated with a control adenovirus that does not express IFN-alpha (Ad5-null) and challenged 1 d later with PRRSV. IFN-alpha levels in all pigs inoculated with the Ad5-pIFN-alpha were elevated the day of challenge (1 d after inoculation), but were undetectable by 3 d after inoculation in the pigs that were not challenged with PRRSV. Pigs inoculated with Ad5-pIFN-alpha and challenged with PRRSV had lower febrile responses, a decreased percentage of lung involvement at 10 d post-infection, delayed viremia and antibody response, and higher serum IFN-alpha levels as a result of PRRSV infection, compared to pigs inoculated with Ad5-null and challenged with PRRSV. These results indicate that IFN-alpha can have protective effects if present during the time of infection with PRRSV.

Coinfection of pigs with porcine respiratory coronavirus and Bordetella bronchiseptica.

Coinfection with two or more pathogens is a common occurrence in respiratory diseases of most species. The manner in which multiple pathogens interact is not always straightforward, however. Bordetella bronchiseptica and porcine respiratory coronavirus (PRCV) are respiratory pathogens of pigs whose relatives, B. pertussis and the SARS virus, cause respiratory disease in humans. In an initial experiment, the effect of coinfection of PRCV and B. bronchiseptica was examined in thirty, 4-week-old pigs (10 pigs/group) that were infected with either PRCV or B. bronchiseptica, or both PRCV and B. bronchiseptica. An additional 10 pigs served as sham infected controls. Five pigs from each group were euthanized at 4 and 10 days post-infection. Gross and histopathological lung lesions were more severe in the coinfected group as compared to the groups infected with B. bronchiseptica or PRCV alone. In order to investigate the potential role of proinflammatory cytokines in disease severity after coinfection, a second experiment was performed to examine cytokine transcription in alveolar macrophages from single and dually infected pigs. A total of 48 pigs were divided equally into groups as above, but 4 pigs from each group were euthanized at 1, 4 and 10 days post-infection. Coinfected pigs showed a greater and more sustained transcription of proinflammatory cytokines, especially IL-6 and MCP-1, than pigs infected with either PRCV or B. bronchiseptica alone. Thus, there appears to be a synergistic effect between PRCV and B. bronchiseptica with regards to proinflammatory cytokine transcription that may partially explain the increased severity of pneumonia in coinfected pigs.

Expression of the dermonecrotic toxin by Bordetella bronchiseptica is not necessary for predisposing to infection with toxigenic Pasteurella multocida.

This experiment was designed to determine whether a Bordetella bronchiseptica mutant that does not produce dermonecrotic toxin (DNT) is still capable of predisposing pigs to infection with toxigenic Pasteurella multocida. Three groups of pigs were initially inoculated intranasally with a wild type B. bronchiseptica that produces DNT, an isogenic mutant of B. bronchiseptica that does not produce DNT, or PBS. All pigs were then challenged intranasally with a toxigenic strain of P. multocida 4 days later. P. multocida was recovered infrequently and in low numbers from pigs initially inoculated with PBS, and no turbinate atrophy was present in these pigs. P. multocida was isolated in similar numbers from the pigs initially inoculated with either the wild type or the DNT mutant of B. bronchiseptica, and turbinate atrophy of a similar magnitude was also seen in pigs from both of these groups. Thus, although the DNT has been shown to be responsible for much of the pathology seen during infection with B. bronchiseptica by itself, infection with non-DNT-producing strains can still predispose to secondary respiratory infections with P. multocida.

Effects of intranasal inoculation with Bordetella bronchiseptica, porcine reproductive and respiratory syndrome virus, or a combination of both organisms on subsequent infection with Pasteurella multocida in pigs.

OBJECTIVE: To determine effects of intranasal inoculation with porcine reproductive and respiratory syndrome virus (PRRSV) or Bordetella bronchiseptica on challenge with nontoxigenic Pasteurella multocida in pigs. ANIMALS: Seventy 3-week-old pigs. PROCEDURE: In experiment 1, pigs were not inoculated (n= 10) or were inoculated with PRRSV (10), P. multocida (10), or PRRSV followed by challenge with P. multocida (10). In experiment 2, pigs were not inoculated (n = 10) or were inoculated with B. bronchiseptica (10) or PRRSV and B. bronchiseptica (10); all pigs were challenged with P. multocida. Five pigs from each group were necropsied 14 and 21 days after initial inoculations. RESULTS: Pasteurella multocida was not isolated from tissue specimens of pigs challenged with P. multocida alone or after inoculation with PRRSV. However, in pigs challenged after inoculation with B. bronchiseptica, P. multocida was isolated from specimens of the nasal cavity and tonsil of the soft palate. Number of bacteria isolated increased in pigs challenged after coinoculation with PRRSV and B. bronchiseptica, and all 3 agents were isolated from pneumonic lesions in these pigs. CONCLUSIONS AND CLINICAL RELEVANCE: Infection of pigs with B. bronchiseptica but not PRRSV prior to challenge with P. multocida resulted in colonization of the upper respiratory tract and tonsil of the soft palate with P. multocida. Coinfection with PRRSV and B. bronchiseptica predisposed pigs to infection of the upper respiratory tract and lung with P. multocida. Porcine reproductive and respiratory syndrome virus and B. bronchiseptica may interact to adversely affect respiratory tract defense mechanisms, leaving pigs especially vulnerable to infection with secondary agents such as P. multocida.

Reduced virulence of a Bordetella bronchiseptica siderophore mutant in neonatal swine.

One means by which Bordetella bronchiseptica scavenges iron is through production of the siderophore alcaligin. A nonrevertible alcaligin mutant derived from the virulent strain 4609, designated DBB25, was constructed by insertion of a kanamycin resistance gene into alcA, one of the genes essential for alcaligin biosynthesis. The virulence of the alcA mutant in colostrum-deprived, caesarean-delivered piglets was compared with that of the parent strain in two experiments. At 1 week of age, piglets were inoculated with phosphate-buffered saline, 4609, or DBB25. Two piglets in each group were euthanatized on day 10 postinfection. The remainder were euthanatized at 21 days postinfection. Clinical signs, including fever, coughing, and sneezing, were present in both groups. Nasal washes performed 7, 14, and 21 days postinoculation demonstrated that strain DBB25 colonized the nasal cavity but did so at levels that were significantly less than those achieved by strain 4609. Analysis of colonization based on the number of CFU per gram of tissue recovered from the turbinate, trachea, and lung also demonstrated significant differences between DBB25 and 4609, at both day 10 and day 21 postinfection. Mild to moderate turbinate atrophy was apparent in pigs inoculated with strain 4609, while turbinates of those infected with strain DBB25 developed no or mild atrophy. We conclude from these results that siderophore production by B. bronchiseptica is not essential for colonization of swine but is required for maximal virulence. B. bronchiseptica mutants with nonrevertible defects in genes required for alcaligin synthesis may be candidates for evaluation as attenuated, live vaccine strains in conventionally reared pigs.

Effects of intranasal inoculation of porcine reproductive and respiratory syndrome virus, Bordetella bronchiseptica, or a combination of both organisms in pigs.

OBJECTIVE: To examine effects of co-infection with porcine reproductive and respiratory syndrome virus (PRRSV) and Bordetella bronchiseptica in pigs. ANIMALS: Forty 3-week-old pigs. Procedure-30 pigs (10 pigs/group) were inoculated with PRRSV, B bronchiseptica, or both. Ten noninoculated pigs were control animals. RESULTS: Clinical signs, febrile response, and decreased weight gain were most severe in the group inoculated with both organisms. The PRRSV was isolated from all pigs in both groups inoculated with virus. All pigs in both groups that received PRRSV had gross and microscopic lesions consistent with interstitial pneumonia. Bordetella bronchiseptica was cultured from all pigs in both groups inoculated with that bacterium. Colonization of anatomic sites by B bronchiseptica was comparable between both groups. Pigs in the group that received only B bronchiseptica lacked gross or microscopic lung lesions, and B bronchiseptica was not isolated from lung tissue. In the group inoculated with B bronchiseptica and PRRSV, 3 of 5 pigs 10 days after inoculation and 5 of 5 pigs 21 days after inoculation had gross and microscopic lesions consistent with bacterial bronchopneumonia, and B bronchiseptica was isolated from the lungs of 7 of those 10 pigs. CONCLUSIONS AND CLINICAL RELEVANCE: Clinical disease was exacerbated in co-infected pigs, including an increased febrile response, decreased weight gain, and B bronchiseptica-induced pneumonia. Bordetella bronchiseptica and PRRSV may circulate in a herd and cause subclinical infections. Therefore, co-infection with these organisms may cause clinical respiratory tract disease and leave pigs more susceptible to subsequent infection with opportunistic bacteria.

Effect of temperature modulation and bvg mutation of Bordetella bronchiseptica on adhesion, intracellular survival and cytotoxicity for swine alveolar macrophages.

Bordetella bronchiseptica causes respiratory disease in swine, yet there are no studies examining the interaction of B. bronchiseptica with swine alveolar macrophages. A swine isolate of B. bronchiseptica was able to adhere to, and survive intracellularly in, swine alveolar macrophages, but the relative ability of the bacteria to accomplish these functions was dependent on its phenotypic phase and culture conditions. More bacteria were observed extracellularly as well as intracellularly by immunofluorescent staining when B. bronchiseptica was cultured at 23 degrees C as compared to 37 degrees C. However, more bacteria cultured at 37 degrees C were found surviving intracellularly after the macrophages were cultured with polymyxin B to kill extracellular bacteria. Similar results were seen in experiments performed with an isogenic Bvg(-) phase-locked mutant of B. bronchiseptica cultured at 37 or 23 degrees C, indicating that another temperature dependent mechanism in addition to bvg may play a role in adhesion and intracellular survival. B. bronchiseptica was cytotoxic for swine alveolar macrophages in the Bvg(+) phase only. The cytotoxicity of B. bronchiseptica for alveolar macrophages, and its ability to survive phagocytosis, are no doubt important to escape from immune clearance mechanisms and establish infection, and could leave the host susceptible to secondary respiratory pathogens.

Evaluation of protective immunity in gilts inoculated with the NADC-8 isolate of porcine reproductive and respiratory syndrome virus (PRRSV) and challenge-exposed with an antigenically distinct PRRSV isolate.

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.

Early colonization of the rat upper respiratory tract by temperature modulated Bordetella bronchiseptica.

The ability of nonmodulated Bvg+ phase cultures, temperature modulated Bvg- phase cultures, and a Bvg- phase-locked mutant of Bordetella bronchiseptica to colonize the rat upper respiratory tract was investigated. Initially, greater numbers of the temperature modulated Bvg- phase bacteria adhered to the nasal cavity of the rats. The temperature modulated Bvg- phase bacteria appeared to be quickly cleared to levels lower than the Bvg+ phase bacteria by 4 h after inoculation and stayed lower until 48 h after inoculation when colonization levels were equal to the Bvg+ phase bacteria. The level of colonization with the Bvg- phase-locked mutant of B. bronchiseptica was lower than both the nonmodulated Bvg+ phase and temperature modulated Bvg- phase cultures and declined over time during the experiment. These findings suggest that there may be increased adherence from an environmental phase to ensure bacteria survive initial clearance mechanisms until the switch to the Bvg+ phase occurs.

The role of biotechnologically engineered vaccines and diagnostics in pseudorabies (Aujeszky's disease) eradication strategies.

Modern-day biotechnology has an almost unlimited number of possibilities for reducing the impact of hereditary and infectious diseases. To date one of its most visible and rewarding applications for veterinary medicine has been in the genetic engineering of vaccines and diagnostics to assist in the eventual eradication of pseudorabies (PR, Aujeszky's disease). In the following review we summarize some of the most pertinent issues relative to PR eradication and point out the present and potential role of biotechnology in achieving our goal.

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.

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).

Duration of homologous porcine reproductive and respiratory syndrome virus immunity in pregnant swine.

The duration of porcine reproductive and respiratory syndrome virus (PRRSV) homologous immunity was tested in this study and found to last for at least 604 days post experimental exposure to field PRRSV. Eleven gilts (group A) received a primary exposure to field PRRSV by either an oronasal (n = 6) or an intrauterine (n = 5) route. The gilts were naturally bred at selected times (143 to 514 days) after primary virus exposure. They were oronasally exposed a second time to the same strain of virus on or about gestation day 90. Ten age-matched control sows free of PRRSV-specific antibody from the same source farm (group B) were naturally bred and were oronasally exposed to aliquots of the homologous challenge virus on or about gestation day 90. Nine of the 11 gilts in group A and all animals in group B became pregnant following one breeding cycle. The two nonpregnant gilts in group A were each naturally bred during four additional estrus cycles and neither became pregnant. They were exposed to homologous challenge virus 562 and 604 days post primary exposure, respectively. All animals were necropsied 21 days post homologous challenge. Sera and alveolar macrophages from each dam, and sera from each fetus were tested for virus. Transplacental infection was detected in 0/9 and 8/10 litters in groups A and B, respectively. Virus was detected in 0/11 and 10/10 of the alveolar macrophage samples collected in groups A and B, respectively. Serum was harvested at selected times throughout the experiment and tested for PRRSV-specific antibody by indirect immunofluorescence microscopy. All gilts in group A were seropositive for the duration of the experiment, and all animals in group B seroconverted following exposure to field PRRSV. This study shows that adult swine can produce a homologous protective immunity after PRRSV exposure that may persist for the production life of the animal.

Comparison of the protective response induced by NYVAC vaccinia recombinants expressing either gp50 or gII and gp50 of pseudorabies virus.

A NYVAC vaccinia vector containing genes for pseudorables virus glycoproteins gII and gp50 was administered to pigs to determine if it would have a greater protective effect than a vector containing the gene for gp50 alone. Both NYVAC vectors protected pigs similarly from virulent pseudorabies virus challenge.

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.

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.

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.

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.

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.