Detection of U.S., Lelystad, and European-like porcine reproductive and respiratory syndrome viruses and relative quantitation in boar semen and serum samples by real-time PCR

Persistence and Retention of Porcine Reproductive and Respiratory Syndrome Virus in Stable Flies (Diptera: Muscidae)

We investigated the acquisition of porcine reproductive and respiratory syndrome (PRRS) virus by the stable fly (Diptera: Muscidae; Stomoxys calcitrans (L.)) through a bloodmeal, and virus persistence in the digestive organs of the fly using virus isolation and quantitative reverse-transcription PCR (qRT-PCR). Stable flies were fed blood containing live virus, modified live vaccine virus, chemically inactivated virus, or no virus. Stable flies acquired PRRSV from the bloodmeal and the amount of virus in the flies declined with time, indicating virus did not replicate in fly digestive tissues. Virus RNA was recovered from the flies fed live virus up to 24 h postfeeding using virus isolation techniques and 96 h using qRT-PCR. We further examined the fate of PRRSV in the hemolymph of the flies following intrathoracic injection to bypass the midgut barrier. PRRSV was detected in intrathoracically inoculated adult stable flies for 10 d using qRT-PCR. In contrast to what we observed in the digestive tract, detectable virus quantities in the intrathoracically inoculated stable flies followed an exponential decay curve. The amount of virus decreased fourfold in the first 3 d and remained stable thereafter, up to 10 d.

Two Commercial Type 1 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV)-Modified Live Vaccines Reduce Seminal Shedding of Type 1 PRRSV but not Type 2 PRRSV in Infected Boars

The objective of this study was to compare the effects of two commercial type 1 porcine reproductive and respiratory syndrome virus (PRRSV)-modified live vaccines on type 1 and type 2 PRRSV shedding in the semen of experimentally infected boars. Upon challenge with PRRSV, unvaccinated boars exhibited an increase in daily rectal temperature (39.4-39.7°C). Vaccination of boars with type 1 PRRSV significantly reduced the amount of type 1 PRRSV load in blood and semen after challenge with type 1 PRRSV, but barely reduced the amount of type 2 PRRSV load in blood and semen after the type 2 PRRSV challenge. There were no significant differences in the reduction of viremia and seminal shedding of type 1 and type 2 PRRSV between the two commercial vaccines. The seminal shedding of PRRSV is independent of viremia. The reduction of type 1 PRRSV seminal shedding coincided with the appearance of type 1 PRRSV-specific interferon-γ secreting cells (IFN-γ-SC) in vaccinated type 1 PRRSV-challenged boars. The frequencies of type 1 PRRSV-specific IFN-γ-SC induced by type 1 PRRSV vaccine are relatively high compared to type 2 PRRSV-specific IFN-γ-SC induced by the same vaccine which may explain why type 1 PRRSV vaccine is more effective in reducing seminal shedding of type 1 PRRSV when compared to type 2 PRRSV in vaccinated challenged boars. These results provide clinical information on how to reduce seminal shedding of type 1 PRRSV in boars using type 1 PRRSV-modified live vaccine.

Comparison of Two Commercial Type 1 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) Modified Live Vaccines against Heterologous Type 1 and Type 2 PRRSV Challenge in Growing Pigs

The objective of the present study was to compare the efficacy of two commercial type 1 porcine reproductive and respiratory syndrome virus (PRRSV) modified live vaccines against heterologous type 1 and type 2 PRRSV challenge in growing pigs. Vaccination with a type 1 PRRSV vaccine reduced the level of viremia after type 1 PRRSV challenge but did not reduce the level of viremia after the type 2 PRRSV challenge in pigs. Increased levels of interleukin-10 (IL-10) stimulated by type 2 PRRSV coincided with the low numbers of type 2 PRRSV-specific interferon gamma-secreting cells (IFN-γ-SC) in vaccinated pigs after type 2 PRRSV challenge, whereas low levels of IL-10 stimulated by type 1 PRRSV coincided with high numbers of type 1 PRRSV-specific IFN-γ-SC in vaccinated pigs after type 1 PRRSV challenge. Additionally, vaccination with the type 1 PRRSV vaccine effectively reduced the lung lesions and type 1 PRRSV nucleic acids in type 1 PRRSV-challenged pigs but did not reduce lung lesions and type 2 PRRSV nucleic acids in type 2 PRRSV-challenged pigs. There were no significant differences between two commercial type 1 PRRSV vaccines against type 1 and type 2 PRRSV challenge based on virological results, immunological responses, and pathological outcomes. This study demonstrates that vaccinating pigs with the type 1 PRRSV vaccine provides partial protection against respiratory disease with heterologous type 1 PRRSV challenge but no protection with heterologous type 2 PRRSV challenge.

Comparison of three commercial one-dose porcine circovirus type 2 (PCV2) vaccines in a herd with concurrent circulation of PCV2b and mutant PCV2b

Porcine circovirus associated disease (PCVAD) occurred in a farm where pigs had been routinely vaccinated with a commercial PCV2a vaccine. A mutant PCV2b (mPCV2b) was isolated from pigs with PCVAD, perhaps implying a perceived vaccine failure. The objective of this study was to determine and compare the efficacy of 3 one-dose PCV2a vaccines of varying antigen type and dose in the same pig farm with concurrent PCV2b and mPCV2b infection based on clinical (average daily weight gain; ADWG), virological (evidence of viremia), immunological (presence of PCV2-specific neutralizing antibody; NA and interferon-γ secreting cells; IFN-γ-SC), and pathological (lymphoid lesion and PCV2 antigen score within lesion) evaluation. Regardless of which commercial PCV2a vaccine was used, vaccinated animals improved ADWG, and reduced the amount of PCV2b and mPCV2b load in the blood compared to unvaccinated animals. The vaccination of piglets at 3 weeks of age effectively induced higher levels of PCV2b- and mPCV2b-specific NA and IFN-γ-SC compared to unvaccinated animals. A reduction in mPCV2b load in the blood coincided with the appearance of both mPCV2b-specific NA and IFN-γ-SC in the vaccinated animals. The microscopic lymphoid lesions and PCV2-antigen scores within the lymph nodes were significantly lower in vaccinated animals. The perceived vaccine failure could not be explained by incomplete protection of the commercial PCV2a vaccine against mPCV2b. The results of the present study demonstrated that currently available commercial PCV2a vaccines are protective against concurrent PCV2b and mPCV2b infection based on clinical, virological, immunological, and pathological evaluations under field conditions.

Cross-protection of a new type 2 porcine reproductive and respiratory syndrome virus (PRRSV) modified live vaccine (Fostera PRRS) against heterologous type 1 PRRSV challenge in growing pigs

The objective of the present study was to determine the cross-protection of a new type 2 porcine reproductive and respiratory syndrome virus (PRRSV) modified live vaccine against heterologous type 1 PRRSV challenge in growing pigs. The mean rectal temperature and respiratory score was significantly (P<0.05) lower in vaccinated challenged pigs than in unvaccinated challenged pigs. Vaccination of pigs with type 2 PRRSV reduced the levels of type 1 PRRSV viremia after challenge with type 1 PRRSV. Vaccinated challenged pigs had significantly (P<0.05) higher frequency of interferon-γ secreting cells and lower levels of interleukin-10 compared to unvaccinated challenged pigs. Vaccination of pigs with the type 2 PRRSV effectively reduced the macroscopic and microscopic lung lesion and the type 1 PRRSV antigens within lung lesions in vaccinated challenged pigs. This study demonstrates partial cross-protection of a new type 2 PRRSV modified live vaccine against heterologous type 1 PRRSV challenge in growing pigs.

Comparison of experimental infection with northern and southern Vietnamese strains of highly pathogenic porcine reproductive and respiratory syndrome virus

The aim of this study was to compare the virulence of northern and southern Vietnamese strains of highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) as assessed by the level of viral replication, gross and microscopical lung lesions and virus distribution in experimentally infected pigs. The northern and southern Vietnamese HP-PRRSV strains share 96.7% (non-structural protein 2) and 99.3% (open reading frame 5) nucleotide identity. On experimental challenge, approximately 50% of pigs infected with northern Vietnamese HP-PRRSV died, while death was not observed in any pigs infected with southern Vietnamese HP-PRRSV. Mean viral titres (expressed as log(10)TCID(50)/ml) were significantly (P <0.05) higher in sera and lungs from pigs infected with the northern Vietnamese HP-PRRSV than from those infected with the southern Vietnamese strain at multiple time points. Lung lesion scores and PRRSV antigen within pulmonary and lymphoid lesions were significantly (P <0.05) higher in pigs infected with northern Vietnamese HP-PRRSV than in those receiving southern Vietnamese HP-PRRSV at multiple time points. PRRSV antigens were observed in cardiac myocytes, gastric and renal tubular epithelial cells and astrocytes and microglia of white matter in the brain from pigs infected with the northern Vietnamese HP-PRRSV strain only. Thus, genetic similarity did not predict the degree of virulence of these strains. Northern Vietnamese HP-PRRSV was more virulent and had extended tissue tropism when compared with southern Vietnamese HP-PRRSV.

Comparison of pathogenicity of highly pathogenic porcine reproductive and respiratory syndrome virus between wild and domestic pigs

The objective of this study was to compare the pathogenicity of highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) infection between wild and domestic pigs based on clinical, immunological, and pathological evaluation. Upon challenge with HP-PRRSV, five wild pigs died compared to none of the domestic. Anti-PRRSV antibody titers were significantly (P < 0.05) higher in wild HP-PRRSV-infected pigs versus the domestic HP-PRRSV-infected pigs at 21 days post inoculation (dpi). Lung lesion scores at 7 dpi were also significantly (P < 0.01) higher in domestic infected pigs than wild infected pigs. The most striking difference was the viral tissue distribution between the wild and domestic HP-PRRSV-infected pigs. HP-PRRSV-positive cells were observed in bronchiolar, gastric, and renal tubular epithelial cells from wild HP-PRRSV-infected pigs only. The results in this study demonstrated a genetic difference exists between wild and domestic pigs, which could results in different clinical signs, immunological responses, and pathological outcomes to HP-PRRSV infection.

An Outbreak of Porcine Reproductive and Respiratory Syndrome Virus in Switzerland Following Import of Boar Semen

An outbreak of porcine reproductive and respiratory syndrome virus (PRRSV) occurred in November 2012 in Switzerland (CH), traditionally PRRSV-free. It was detected after a German boar stud informed a semen importer about the detection of PRRSV during routine monitoring. Tracing of semen deliveries revealed 26 Swiss sow herds that had used semen from this stud after its last negative routine monitoring and 62 further contact herds. All herds were put under movement restrictions and examined serologically and virologically. As a first measure, 59 sows from five herds that had previously been inseminated with suspicious semen were slaughtered and tested immediately. Investigations in the stud resulted in 8 positive boars with recent semen deliveries to CH (Seven with antibodies and virus, one with antibodies only). In one boar out of six tested, virus was detected in semen. Of the 59 slaughtered sows, five from three herds were virus-positive. In one herd, the virus had spread, and all pigs were slaughtered or non-marketable animals euthanized. In the remaining herds, no further infections were detected. After confirmatory testings in all herds 3 weeks after the first examination gave negative results, restrictions were lifted in January 2013, and Switzerland regained its PRRSV-free status. The events demonstrate that import of semen from non-PRRS-free countries--even from negative studs--poses a risk, because monitoring protocols in boar studs are often insufficient to timely detect an infection, and infections of sows/herds occur even with low numbers of semen doses. The outbreak was eradicated successfully mainly due to the high disease awareness of the importer and because immediate actions were taken before clinical or laboratory diagnosis of a single case in the country was made. To minimize the risk of an introduction of PRRSV in the future, stricter import guidelines for boar semen have been implemented.

A new modified live porcine reproductive and respiratory syndrome vaccine improves growth performance in pigs under field conditions

The change in growth performance resulting from a new modified live porcine reproductive and respiratory syndrome (PRRS) vaccine was evaluated under field conditions for registration with the government as guided by the Republic of Korea's Animal and Plant Quarantine Agency. Three farms were selected based on their history of PRRS-associated respiratory diseases. On each farm, a total of 45 3-week-old pigs were randomly allocated to one of two treatment groups, (i) vaccinated (n = 25) or (ii) control (n = 20) animals. A new modified live PRRSV vaccine increased market weight by 1.26 kg/pig (104.71 kg versus 103.45 kg; P < 0.05) and decreased mortality by 17% (1.33% versus 18.33%; P < 0.05). Pathological examination indicated that vaccination effectively reduced microscopic lung lesions compared with control animals on the 3 farms. Thus, the new modified live PRRS vaccine improved growth performance and decreased mortality and lung lesions when evaluated under field conditions.

Comparison of porcine circovirus type 2 (PCV2)-associated lesions produced by co-infection between two genotypes of PCV2 and two genotypes of porcine reproductive and respiratory syndrome virus

The objective of this study was to compare the virulence and pathogenicity of a combination of concurrent infections of two genotypes of porcine circovirus type 2 (PCV2) and two genotypes of porcine reproductive and respiratory syndrome virus (PRRSV) in terms of PCV2 viraemia, and PCV2-associated lesions and antigens in co-infected pigs. Pigs with PCV2a (or 2b)/type 1 (or type 2) PRRSV had significantly (P<0.05) higher mean clinical respiratory scores and lower average daily weight gain compared with pigs with PCV2a (or 2b). Co-infection induced significantly lower levels of anti-PCV2 and anti-PRRSV IgG antibodies than infection with one genotype alone, regardless of the genotype of the two viruses. Pigs with PCV2a (or 2b)/type 2 PRRSV had significantly (P<0.05) higher levels of PCV2 viraemia, more severe PCV2-associated lesions, and more PCV2 DNA within the lesions compared with pigs with PCV2a (or 2b)/type 1 PRRSV. However, there was no significant difference in these parameters in pigs with PCV2a/type 2 PRRSV or PCV2b/type 2 PRRSV. The results of this study demonstrate significant differences in the virulence and pathogenicity of type 1 and type 2 PRRSV but no significant differences in the virulence and pathogenicity of PCV2a and PCV2b with respect to the production of PCV2-associated lesions.

Simultaneous detection and differentiation of highly virulent and classical Chinese-type isolation of PRRSV by real-time RT-PCR

Porcine reproductive and respiratory syndrome (PRRS) is a leading disease in pig industry worldwide and can result in serious economic losses each year. The PRRS epidemic situation in China has been very complicated since the unprecedented large-scale highly pathogenic PRRS (HP-PRRS) outbreaks in 2006. And now the HP-PRRS virus (HP-PRRSV) and classical North American type PRRSV strains have coexisted in China. Rapid differential detection of the two strains of PRRSV is very important for effective PRRS control. The real-time RT-PCR for simultaneous detection and differentiation of HP-PRRSV and PRRSV by using both SYBR Green and TaqMan probes was developed and validated. Both assays can be used for rapid detection and strain-specific identification of HP-PRRSV and PRRSV. However, the TaqMan probe method had the highest detection rate whereas the conventional RT-PCR was the lowest. The real-time RT-PCR developed based on SYBR Green and TaqMan probe could be used for simultaneous detection and differentiation of HP-PRRSV and PRRSV in China, which will benefit much the PRRS control and research.

Evaluation of the efficacy of a new modified live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine (Fostera PRRS) against heterologous PRRSV challenge

The objective of this study was to evaluate a new modified live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine (Fostera PRRS, Zoetis, Florham, NJ, USA) that was based on a virulent US PRRSV isolate (P129) attenuated using CD163-expressing cell lines. Sixty-four PRRSV-seronegative 3-week-old pigs were randomly divided into the following four groups: vaccinated challenged (group 1), vaccinated unchallenged (group 2), unvaccinated challenged (group 3), and unvaccinated unchallenged (group 4). The pigs in groups 1 and 2 were immunized with a 2.0 mL dose of modified live PRRSV vaccine at 21 days of age, according to the manufacturer's recommendations. At 56 days of age (0 days post-challenge), the pigs in groups 1 and 3 were inoculated intranasally with 3 mL of tissue culture fluid containing 10(5) 50% tissue culture infective dose (TCID50)/mL of PRRSV (SNUVR090851 strain, fourth passage in MARC-145 cells). Vaccinated challenged pigs exhibited significantly lower (P<0.05) respiratory scores, viremia, macroscopic and microscopic lung lesion scores, and PRRSV-antigen with interstitial pneumonia than unvaccinated challenged pigs. The induction of PRRSV-specific IFN-γ-SCs by the new modified live PRRSV vaccine produced a protective immune response, leading to the reduction of PRRSV viremia. Although the new modified live PRRSV vaccine is not effective against heterologous PRRSV challenge, the new modified live PRRSV vaccine was able to reduce the levels of viremia and nasal shedding, and severity of PRRSV-induced lesions after challenging virus under experimental conditions.

Interaction of porcine circovirus type 2 and Mycoplasma hyopneumoniae vaccines on dually infected pigs

The objective of this study was to determine the effects of porcine circovirus type 2 (PCV2) and Mycoplasma hyopneumoniae vaccinations on disease severity in an experimental PCV2-M. hyopneumoniae dual challenge model. Vaccine effectiveness was evaluated using microbiological (PCV2 viremia and M. hyopneumoniae nasal shedding), immunological (neutralizing antibodies and interferon-γ-secreting cells), and pathological (gross lung lesions, histopathologic pulmonary and lymphoid lesions, and the presence of PCV2 antigen and M. hyopneumoniae DNA within the lesions) evaluations. Although M. hyopneumoniae potentiates the severity of PCV2-associated lesions and lesion-associated PCV2 antigen in dually challenged pigs, vaccination against M. hyopneumoniae alone did not reduce PCV2 viremia, PCV2-induced lesions, or PCV2 antigen in dually challenged pigs. In addition, vaccination against PCV2 did not reduce the nasal shedding of M. hyopneumoniae, the M. hyopneumoniae-induced pulmonary lesions or the lesion-associated M. hyopneumoniae DNA in dually challenged pigs. Dual challenge with PCV2 and M. hyopneumoniae did not interfere with the induction of active immunity induced by a previous single vaccination for either PCV2 or M. hyopneumoniae. The results of this study demonstrated that (i) vaccination against M. hyopneumoniae alone did not decrease the potentiation of PCV2-induced lesions by M. hyopneumoniae and (ii) vaccination against PCV2 alone decreased the potentiation of PCV2-induced lesions by M. hyopneumoniae in dually challenged pigs.

Vaccination of sows against type 2 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) before artificial insemination protects against type 2 PRRSV challenge but does not protect against type 1 PRRSV challenge in late gestation

The objective of the present study was to determine the effects of the commercially available type 2 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV)-based modified live vaccine against type 1 and type 2 PRRSV challenge in pregnant sows. Half of the sows in the study were vaccinated with a type 2 PRRSV-based vaccine 4 weeks prior to artificial insemination while the other half remained non-vaccinated. Sows were then challenged intranasally with type 1 or type 2 PRRSV at 93 days of gestation. The sows which received the type 2 PRRSV-based vaccine followed by type 2 PRRSV challenge had significantly higher neutralizing antibody titers against type 2 PRRSV than they did against type 1 PRRSV. These same sows had higher frequencies of IFN-γ-secreting cells when stimulated with type 2 PRRSV compared to those stimulated with type 1 PRRSV. Subsequent virological evaluation demonstrated that the type 2 PRRSV-based vaccine reduced the type 2 PRRSV load but not the type 1 PRRSV load present in the blood of the sows. Additionally, vaccination of pregnant sows with the type 2 PRRSV-based vaccine effectively reduced the level of type 2 PRRSV nucleic acids observed in fetal tissues from type 2 PRRSV-challenged sows but did not reduce the level of type 1 PRRSV nucleic acid observed in fetal tissues from type 1 PRRSV-challenged sows. This study demonstrates that the vaccination of pregnant sows with the type 2 PRRSV-based vaccine protects against type 2 PRRSV challenge but does not protect against type 1 PRRSV challenge.

Comparison of four commercial one-dose porcine circovirus type 2 (PCV2) vaccines administered to pigs challenged with PCV2 and porcine reproductive and respiratory syndrome virus at 17 weeks postvaccination to control porcine respiratory disease complex under Korean field conditions

Under Korean field conditions, coinfection with porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) is most commonly observed in porcine respiratory disease complex (PRDC). Despite the wide use of PCV2 vaccination, PRDC remains a serious respiratory problem. Thus, the objective of this study was to determine and compare the efficacy of 4 one-dose PCV2 vaccines on 3-week-old pigs with an experimental PCV2-PRRSV challenge at 17 weeks postvaccination. Regardless of which commercial PCV2 vaccine was used, the vaccination of piglets at 3 weeks of age was efficacious against cochallenge of PCV2 and PRRSV, on the basis of growth performance and PCV2-associated lesions. However, the inactivated chimeric PCV1-2 and the PCV2 vaccines induced higher PCV2-specific neutralizing antibody (NA) titers and PCV2-specific gamma interferon-secreting cells and lower PCV2 viremia levels than the two PCV2 subunit vaccines. The vaccination of piglets against PCV2 at 3 weeks of age was effective in reducing PCV2 viremia and PCV2-associated lesions during the finishing period, which is an age at which pigs are frequently affected by PRDC caused by coinfection with PCV2 and PRRSV under Korean field conditions.

Comparison of viremia of type II porcine reproductive and respiratory syndrome virus in naturally infected pigs by zip nucleic acid probe-based real-time PCR

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) is a RNA virus with high genetic variation. This virus causes significant economic losses in most pig-producing countries. The clinical presentation of PRRSV ranges from asymptomatic to devastating. In this study, we developed a sensitive and specific zip nucleic acid probe-based real-time PCR assay to evaluate the viremia of natural PRRSV-infected pigs in Taiwan. Serum samples were collected from 577 pigs aged 5–12 weeks. These include 444 clinically healthy pigs and 133 symptomatic pigs were confirmed to have porcine respiratory disease complex (PRDC).

Results

Viremia was quantified in 79 of the 444 (17.8%) clinically healthy pigs and in 112 of the 133 (84.2%) PRDC cases. Viremias were significantly more common in pigs with PRDC compared with the clinically healthy pigs (P <0.0001). These results suggest that a high viral load is a major feature of PRRSV-affected pigs.

Conclusions

ZNA probe-based real-time PCR can be a useful tool to diagnose symptomatic and asymptomatic PRRSV-infected pigs. The presence of this marker in a sample of animals with high PRRSV loads (>10^4.2 PRRSV genomes/μl of serum) seems to indicate that it correlates with the presence of PRDC in pigs.

Fresh Pork and Porcine Reproductive and Respiratory Syndrome Virus: Factors Related to the Risk of Disease Transmission

Porcine reproductive and respiratory syndrome virus (PRRS) is a highly infectious virus. Experimentally, the disease can be induced in naïve pigs by the oral, intranasal and intramuscular routes. Depending on the virulence of the strain of the virus and the age of the pig, peak viremia can occur within 7 days of infection, and live virus can be isolated from blood or lymph nodes for several months post-infection. Young pigs tend to develop higher titres of viremia than older pigs infected by the same route and dose with the same strain of virus. Porcine reproductive and respiratory syndrome virus survives in pork harvested from infected pigs for extended periods at temperatures of -20 or -70°C. In experimentally infected pigs, survival of PRRS virus in muscle held at 4°C has been demonstrated for at least 7 days, and infectivity of the virus in these samples was confirmed by bioassay. The optimal pH range for the survival of PRRS virus is thought to be 6.0 to 7.5. The elevated pH of non-meat tissues (generally one pH unit higher) is likely to favour extended survival of PRRS virus in pig carcasses from which all superficial and deep lymph nodes have not been removed. It is likely that exsanguinated carcasses held at 4°C retain sufficient blood or lymph tissue to contain infective doses of PRRS virus. Porcine reproductive and respiratory syndrome virus is rapidly inactivated by heat, providing a predictable method to ensure that pork tissues are free of viable virus and feeding of cooked swill or garbage should not constitute a risk to pigs. While the probability of viable PRRS virus being present in a pig carcass may be low, the risk is not zero. The importation of raw pork into countries where PRRS is not endemic represents a hazard with potentially severe economic consequences.

Comparison of specimens for detection of porcine reproductive and respiratory syndrome virus infection in boar studs

Porcine reproductive and respiratory syndrome virus (PRRSV)-contaminated semen from boars is a route of transmission to females, and early detection of PRRSV infection in boars is a key component in sow farm biosecurity. The purpose of this study was to determine the optimum diagnostic specimen(s) for the detection of acute PRRSV infection in boars. Individually housed boars (n = 15) were trained for semen and oral fluid collection and then vaccinated with a commercial PRRSV modified live virus vaccine. Starting on the day of vaccination and for 14 days thereafter, oral fluid specimens were collected daily from all boars. The 15 boars were subdivided into three groups of 5, and serum, blood swabs and 'frothy saliva' were collected at the time of semen collection on a 3-day rotation. Frothy saliva, derived from the submandibular salivary gland, is produced by aroused boars. Semen was centrifuged, and semen supernatant and cell fractions were tested separately. All samples were randomly ordered and then tested by PRRSV real-time quantitative reverse-transcription polymerase chain reaction assay (rRT-PCR) and PRRSV antibody ELISA. In this study, a comparison of serum, blood swab, and oral fluid rRT-PCR results found no statistically significant differences in the onset of detection or proportion of positives, but serum was numerically superior to oral fluids for early detection. Serum and oral fluid provided identical rRT-PCR results at ≥ 5 day post-vaccination. Likewise, the onset of detection of PRRSV antibody in serum, oral fluid and frothy saliva was statistically equivalent, with serum results again showing a numerical advantage. These results showed that the highest assurance of providing PRRSV-negative semen to sow farms should be based on rRT-PCR testing of serum collected at the time of semen collection. This approach can be augmented with oral fluid sampling from a random selection of uncollected boars to provide for statistically valid surveillance of the boar stud.

Comparative pathogenesis of type 1 (European genotype) and type 2 (North American genotype) porcine reproductive and respiratory syndrome virus in infected boar

Background

Porcine reproductive and respiratory syndrome virus (PRRSV) now has two main genotypes, genotype 1 (European) and genotype 2 (North American). There is a lack of data on the comparison of pathogenicity of the two genotypes in boars. The objectives of the present study were to evaluate the amount of PRRSV present in semen over time and compare the viral distribution and microscopic lesions of type 1 and type 2 PRRSV-infected boars.

Methods

Twenty-four 8-month-old PRRSV-naïve Duroc boars were randomly allocated to 3 treatment groups. The boars in groups 1 (n = 9) and 2 (n = 9) were intranasally inoculated with type 1 or type 2 PRRSV, respectively. The boars in groups 1 (n = 6) served as negative controls. Semen and blood samples were collected up to 35 days post-inoculation (dpi), and necropsies were performed on 14, 21, and 35 dpi.

Results

There were no significant differences in the genomic copy number of PRRSV, microscopic testicular lesion score, number of PRRSV-positive germ cells, or number of apoptotic cells between the type 1 and type 2 PRRSV-infected boars throughout the experiment. Histopathological changes were manifested by the desquamation of spermatocytes and the presence of multinucleated giant cells in seminiferous tubules of both type 1 and type 2 PRRSV-infected boars. The distribution of PRRSV-positive cells was focal; the virus was found in single germ cells or small clusters of germ cells, localized to the spermatogonia, spermatocytes, spermatids, and non-sperm cells in type 1 and type 2 PRRSV-infected boars.

Conclusions

The results of this study demonstrated that two genotypes of PRRSV do not have significantly different virulence toward the male reproductive system of pigs.

Immune response to ORF5a protein immunization is not protective against porcine reproductive and respiratory syndrome virus infection

Porcine reproductive and respiratory syndrome virus (PRRSV) is an enveloped RNA virus responsible for PRRS in swine, a disease with globally significant animal welfare and economic concerns. There is no specific treatment and variably effective immune protection. Molecular mechanisms responsible for virulence, pathogenesis and protective immune response remain poorly understood. These factors limit progress toward development of effective measures for prevention and treatment of PRRS. A novel PRRSV ORF5a protein, encoded in an open reading frame (ORF) that overlaps the major envelope glycoprotein GP5 ORF, was recently identified. Because ORF5a is highly conserved in diverse PRRSV isolates, is a structural protein in the virion, and elicits a specific antibody response in infected pigs, we investigated its potential role in immune protection against PRRSV infection. Pigs immunized with ORF5a protein had robust serologic responses. However, the antibodies did not neutralize virus, and immunity did not protect against challenge infection. We conclude from these findings that the ORF5a antibody response is neither neutralizing nor protective.

Effect of saliva stabilisers on detection of porcine reproductive and respiratory syndrome virus in oral fluid by quantitative reverse transcriptase real-time PCR

This study evaluated the effect of extraction-amplification methods, storage temperature and saliva stabilisers on detection of porcine reproductive and respiratory syndrome virus (PRRSV) RNA by quantitative reverse transcriptase real-time PCR (qRT-PCR) in porcine oral fluid. The diagnostic performance of different extraction-amplification methods was examined using a dilution series of oral fluid spiked with PRRSV. To determine RNA stability, porcine oral fluid, with or without commercially available saliva stabilisers, was spiked with PRRSV, stored at 4°C or room temperature and tested for the presence of PRRSV RNA by qRT-PCR. PRRSV RNA could be detected in oral fluid using all extraction-amplification combinations, but the limit of detection varied amongst different combinations. Storage temperature and saliva stabilisers had an effect on the stability of PRRSV RNA, which could only be detected for 7 days when PRRSV spiked oral fluid was kept at 4°C or stabilised at room temperature with a commercial mRNA stabiliser.

Pathogenesis of type 1 (European genotype) porcine reproductive and respiratory syndrome virus in male gonads of infected boar

The objective of this study was to determine the pathogenesis of experimental infection with a type 1 porcine reproductive and respiratory syndrome virus (PRRSV) by defining the sites of viral replication and apoptosis in male gonads from infected boars for a period of 21 days after intranasal inoculation. Microscopically, hypospermatogenesis and abundant germ cell depletion and death were observed in the testes. Such germ cell death occurs by apoptosis, as determined by a characteristic histological patterns and evidence of massive DNA fragment detected in situ terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) reaction. PRRSV was detected in the testicular tissue of infected boars only. Viral nucleic acid was localized in spermatogonia, spermatocytes and spermatids but not in the vesicular and bulbourethral gland. In serial sections, PRRSV-positive cells did not co-localized with apoptotic cells. TUNEL-positive apoptotic cells were more numerous than PRRSV-positive cells in testicular sections. The present study demonstrated that type 1 PRRSV infects the spermatogonia and their progeny, and induces apoptosis in these germ cells.

Risk assessment of the introduction of porcine reproductive and respiratory syndrome virus via boar semen into Switzerland as an example of a PRRSV-free country

Switzerland is currently porcine reproductive and respiratory syndrome virus (PRRSV) free, but semen imports from PRRSV-infected European countries are increasing. As the virus can be transmitted via semen, for example, when a free boar stud becomes infected, and the risk of its import in terms of PRRSV introduction is unknown, the annual probability to accidentally import the virus into Switzerland was estimated in a risk assessment. A quantitative stochastic model was set up with data comprised by import figures of 2010, interviews with boar stud owners and expert opinion. It resulted in an annual median number of 0.18 imported ejaculates (= imported semen doses from one collection from one donor) from PRRSV-infected boars. Hence, one infected ejaculate would be imported every 6 years and infect a mean of 10 sows. These results suggest that under current circumstances, there is a substantial risk of PRRSV introduction into Switzerland via imported boar semen and that measures to enhance safety of imports should be taken. The time from infection of a previously negative boar stud to its detection had the highest impact on the number of imported 'positive' ejaculates. Therefore, emphasis should be placed on PRRSV monitoring protocols in boar studs. Results indicated that a substantial increase in safety could only be achieved with much tighter sampling protocols than currently performed. Generally, the model could easily be customized for other applications like other countries or regions or even sow farms that want to estimate their risk when purchasing semen from a particular boar stud.

Comparative effects of vaccination against porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) in a PCV2-PRRSV challenge model

The objective of the present study was to determine the effects of porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) vaccinations in an experimental PCV2-PRRSV challenge model, based on virological (viremia), immunological (neutralizing antibodies [NAs], gamma interferon-secreting cells [IFN-γ-SCs], and CD4(+) CD8(+) double-positive cells), and pathological (lesions and antigens in lymph nodes and lungs) evaluations. A total of 72 pigs were randomly divided into 9 groups (8 pigs per group): 5 vaccinated and challenged groups, 3 nonvaccinated and challenged groups, and a negative-control group. Vaccination against PCV2 induced immunological responses (NAs and PCV2-specific IFN-γ-SCs) and reduced PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. However, vaccination against PCV2 did not affect the PRRSV immunological responses (NAs and PRRSV-specific IFN-γ-SCs), PRRSV viremia, PRRSV-induced lesions, or PRRSV antigens in the dually infected pigs. Vaccination against PRRSV did not induce immunological responses (PRRSV-specific IFN-γ-SCs) or reduce PRRSV viremia, PRRSV-induced lesions, or PRRSV antigens in the dually infected pigs. In addition, vaccination against PRRSV increased PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. In summary, vaccination against PCV2 reduced PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. However, vaccination against PRRSV increased PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. Therefore, the PCV2 vaccine decreased the potentiation of PCV2-induced lesions by PRRSV in dually infected pigs. In contrast, the PRRSV vaccine alone did not decrease the potentiation of PCV2-induced lesions by PRRSV in dually infected pigs.

Development of indirect ELISAs for differential serodiagnosis of classical and highly pathogenic porcine reproductive and respiratory syndrome virus

The objective of this study was to develop two indirect enzyme-linked immunosorbent assays (iELISAs) for detection of serum antibodies against classical vaccine strain of porcine reproductive and respiratory syndrome virus (PRRSV) and highly pathogenic PRRSV (HP-PRRSV). To detect the common antibodies against classical and HP-PRRSV, the coating antigen used in the iELISA (designated iELISA-180) was the antigen of Nsp2-180, the 180aa at amino terminal of Nsp2. To detect the different antibodies against classical and HP-PRRSV, the coating antigen in the second iELISA (designated iELISA-D29) was Nsp2-D29, the deleted 29aa in Nsp2 of HP-PRRSV. The antigen concentration and serum dilutions were optimized using a draughtboard titration. The cut-off values of 0.361 at OD(450nm) for the iELISA-180 and 0.27 at OD(450nm) for the iELISA-D29 were determined by testing a panel of 120 classical PRRSV positive and 198 PRRSV negative pig serum samples, which generated the specificity of 97.1% and 96.7%, the sensitivity of 96.9% and 96.3% for iELISA-180 and iELISA-D29, respectively. The agreements between the Western blot and iELISA-180 and iELISA-D29 were 98%, 96.7%, respectively. The developed iELISAs can be used to differentiate serologically HP-PRRSV from the vaccinated or classical PRRSV in clinical serum samples.

Detection of VR-2332 strain of porcine reproductive and respiratory syndrome virus type II using an aptamer-based sandwich-type assay

Porcine reproductive and respiratory syndrome virus (PRRSV) causes porcine reproductive and respiratory syndrome disease (PRRS), a disease that has a significant and economic impact on the swine industry. In this study, single-stranded DNA (ssDNA) aptamers with high specificity and affinity against VR-2332 strain of PRRSV type II were successfully obtained. Of 19 candidates, the LB32 aptamer was found to be the most specific and sensitive to VR-2332 strain according to an aptamer-based surface plasmon resonance (SPR) analysis. The detection of VR-2332 of PRRSV type II was successfully accomplished using the enzyme-linked antibody-aptamer sandwich (ELAAS) method. The detection limit of ELAAS was 4.8 × 10(0) TCID(50)/mL that is comparable to some of the previous reports of the PCR-based detection but does not require any complicated equipment or extra costs. Moreover, this ELAAS-based PRRSV detection showed similar sensitivity for both the VR-2332 samples spiked in diluted swine serum and in buffer. Therefore, this VR-2332 strain-specific aptamer and its assay method with high specificity can be used as an alternative method for the fast and precise detection of PRRSV.

Comparison of commercial real-time reverse transcription-PCR assays for reliable, early, and rapid detection of heterologous strains of porcine reproductive and respiratory syndrome virus in experimentally infected or noninfected boars by use of different sample types

The aims of this study were to compare three commercial porcine reproductive and respiratory syndrome virus (PRRSV) real-time reverse transcription-PCR (RT-PCR) assays for detection of genetically diverse PRRSV isolates in serum, semen, blood swabs, and oral fluids collected from experimentally infected boars and to evaluate the effects of sample pooling. Six groups of three boars negative for PRRSV were each inoculated with one of six PRRSV isolates (sharing 55 to 99% nucleotide sequence identity in ORF5). Samples were collected on days -2, 1, 3, 5, 7, 14, and 21 postinoculation (p.i.) and tested by one of three commercially available real-time RT-PCR assays (VetMax from Applied Biosystems, Foster City, CA [abbreviated AB]; VetAlert from Tetracore, Rockville, MD [TC]; and AcuPig from AnDiaTec GmbH, Kornwestheim, Germany [AD]). At day 1 p.i., all assays detected at least one positive sample in each group. The highest detection rates were on days 3 and 5 p.i. Between days 1 and 7 p.i., serum samples had the highest detection rate (90%) with 100% agreement between tests, followed by blood swabs (kappa value of 0.97) and semen (kappa value of 0.80). Oral fluids had the lowest detection rates (AB, 55%; TC, 41%; AD, 46%) and the highest disagreement between kits (kappa value of 0.63). Pools of five samples did not reduce the detection rates if there was one positive sample with a large amount (cycle threshold, <30) of viral RNA in the pool. Serum and blood swab samples had shorter turnaround times for RNA extraction. The AB assay had a 1.6-times-shorter PCR time. In summary, serum and blood swabs had the best performance with highest detection rates and agreement between assays and the shortest turnaround times.

Identifying an outbreak of a novel swine disease using test requests for porcine reproductive and respiratory syndrome as a syndromic surveillance tool

Background

Animal disease monitoring and surveillance are crucial for ensuring the health of animals, humans and the environment. Many studies have investigated the utility of monitoring syndromes associated with data from veterinary laboratory submissions, but no research has focused on how negative test results from a veterinary diagnostic laboratory data can be used to improve our knowledge of disease outbreaks. For example, if a diagnostic laboratory was seeing a disproportionate number of negative test results for a known disease could this information be an indication of a novel disease outbreak? The objective of this study was to determine the association between the porcine circovirus associated disease (PCVAD) outbreak in Ontario 2004–2006 and the results of porcine reproductive and respiratory syndrome virus (PPRSV) enzyme-linked immunosorbent assay (ELISA) and the results of PRRSV polymerase chain reaction (PCR) diagnostic tests requested by veterinarians.

Results

Retrospective data were collected from the Animal Health Laboratory (AHL) at the University of Guelph, Guelph, Ontario Canada and were comprised of weekly counts of PRRSV ELISA and PRRSV PCR diagnostic tests requested by swine practitioners from 2000–2007. The results of the PRRSV ELISA and PRRSV PCRs were analysed separately in two models using logistic regression with the dependent variables being: the weekly probability of PRRSV ELISA positivity, and the weekly probability of PRRSV PCR positivity, respectively. The weekly probability of PRRSV PCR positivity decreased during the PVCAD outbreak (OR=0.66, P=0.01). The weekly probability of PRRSV ELISA positivity was not associated with the PCVAD outbreak.

Conclusions

The results of this study showed that during the PCVAD outbreak in Ontario from December 2004-May 2006, the probability of a positive PRRSV PCR at the AHL decreased. We conclude that when a decrease in test positivity occurs for a known disease, it may suggest that a new disease agent is emerging in the population. Hence, monitoring the test results of commonly used first-order tests for a known disease (e.g. PRRSV) has the potential to be a unique form of syndromic data for the timely identification of novel disease outbreaks in swine populations.

Comparison of the virulence of European and North American genotypes of porcine reproductive and respiratory syndrome virus in experimentally infected pigs

The objective of this study was to compare the virulence of Korean types 1 and 2 porcine reproductive and respiratory syndrome virus (PRRSV) isolated from weaned pigs with respiratory disease. Affected pigs were within the same herd and animals infected with type 2 virus had significantly higher mean rectal temperatures than those with type 1 virus between days 2 and 9 post-inoculation (P<0.05). Similarly, mean serum viral titres, expressed as tissue culture infective doses 50% (TCID50)/mL, as well as macroscopic and microscopic pulmonary lesion scores, were significantly higher at multiple time points in pigs infected with type 2 PRRSV compared to those infected with type 1 virus. Mean numbers of PRRSV-positive cells/unit area of lungs and lymph nodes were also significantly higher in type 2 PRRSV infected pigs. This study demonstrates that type 2 PRRSV is more virulent than type 1 PRRSV in this experimental setting as reflected by the pulmonary pathology induced, the extent of virus distribution, and oral shedding of the virus.

Evaluation of monoclonal antibody-based immunohistochemistry for the detection of European and North American Porcine reproductive and respiratory syndrome virus and a comparison with in situ hybridization and reverse transcription polymerase chain reaction

The objective of the present study was to compare the ability of 2 monoclonal antibodies (mAbs; SDOW17 and SR30) to detect types 1 and 2 Porcine reproductive and respiratory syndrome virus (PRRSV) in formalin-fixed, paraffin-embedded (FFPE) lung tissues by immunohistochemistry (IHC) and to compare the immunohistochemical results with in situ hybridization (ISH) and reverse transcription nested polymerase chain reaction (RT-nPCR) detection techniques. Lungs from 30 experimentally infected pigs (15 pigs with each genotype of PRRSV) and 20 naturally infected pigs (10 pigs with each genotype of PRRSV) with types 1 and 2 PRRSV, respectively, were used for the IHC, ISH, and RT-nPCR analyses. The SR30 mAb-based IHC detected significantly more type 1 PRRSV-positive cells in the accessory and caudal lobes from the experimentally infected pigs at 7 (P = 0.025) and 14 (P = 0.018) days postinoculation, respectively, compared to the SDOW17 mAb-based IHC. The results demonstrated that SR30 mAb-based IHC is useful for detecting both types 1 and 2 PRRSV antigen in FFPE lung tissues.

Evaluation of immune responses to porcine reproductive and respiratory syndrome virus in pigs during early stage of infection under farm conditions

BACKGROUND

Porcine reproductive and respiratory syndrome virus (PRRSV) causes chronic, economically devastating disease in pigs of all ages. Frequent mutations in the viral genome result in viruses with immune escape mutants. Irrespective of regular vaccination, control of PRRSV remains a challenge to swine farmers. In PRRSV-infected pigs, innate cytokine IFN-α is inhibited and the adaptive arm of the immunity is delayed. To elucidate both cellular and innate cytokine responses at very early stages of PRRSV infection, seven weeks old pigs maintained on a commercial pig farm were infected and analyzed.

RESULTS

One pig in a pen containing 25 pigs was PRRSV infected and responses from this pig and one penmate were assessed two days later. All the infected and a few of the contact neighbor pigs were viremic. At day 2 post-infection, approximately 50% of viremic pigs had greater than 50% reduction in NK cell-mediated cytotoxicity, and nearly a 1-fold increase in IFN-α production was detected in blood of a few pigs. Enhanced secretion of IL-4 (in ~90%), IL-12 (in ~40%), and IL-10 (in ~20%) (but not IFN-γ) in PRRSV infected pigs was observed. In addition, reduced frequency of myeloid cells, CD4(-)CD8(+) T cells, and CD4(+)CD8(+) T cells and upregulated frequency of lymphocytes bearing natural T regulatory cell phenotype were detected in viremic pigs. Interestingly, all viremic contact pigs also had comparable immune cell modulations.

CONCLUSION

Replicating PRRSV in both infected and contact pigs was found to be responsible for rapid modulation in NK cell-meditated cytotoxicity and alteration in the production of important immune cytokines. PRRSV-induced immunological changes observed simultaneously at both cellular and cytokine levels early post-infection appear to be responsible for the delay in generation of adaptive immunity. As the study was performed in pigs maintained under commercial environmental conditions, this study has practical implications in design of protective vaccines.

Pathogenesis of Korean type 1 (European genotype) porcine reproductive and respiratory syndrome virus in experimentally infected pigs

The aim of this study was to elucidate the pathogenesis of experimental infection with Korean type 1 porcine reproductive and respiratory syndrome virus (PRRSV) by defining the virus distribution, sites of viral replication, viraemia and gross and microscopical lesions in conventional pigs studied for 28 days after intranasal inoculation. Mean rectal temperature was significantly higher in infected pigs than in negative control pigs at 2 days post inoculation (dpi) (P=0.004), 3 dpi (P<0.001), 4 dpi (P=0.003) and 5 dpi (P=0.034). The log(10)TCID(50)/ml of type 1 PRRSV increased significantly at 0-1 dpi (P=0.024) and 5-7 dpi (P=0.029), but decreased at 10-14 dpi (P=0.026) and 14-21 dpi (P=0.012) in infected pigs. Infected pigs developed multifocal, tan-mottled areas of lung tissue with irregular and indistinct borders. Microscopical lesions, when present, were multifocal, mild to moderate, generally most extensive at 5-7 dpi (P=0.036), and were nearly resolved at 28 dpi. Type 1 PRRSV nucleic acid and antigen were detected exclusively within the cytoplasm of macrophages and type I and II pneumocytes. The score for PRRSV-positive cells increased at 3-7 dpi (P<0.05) and decreased at 10-14 dpi (P=0.034) in infected pigs. Thus, respiratory disease was reproduced in conventional pigs by infection with Korean type 1 PRRSV.

Effects of North American porcine reproductive and respiratory syndrome virus (PRRSV)-based modified live vaccines on preimmunized sows artificially inseminated with European PRRSV-spiked semen

The objective of the present study was to determine if the European porcine reproductive and respiratory syndrome virus (PRRSV) can be transmitted via spiked semen to preimmunized sows and induce reproductive failure. Sows were immunized with the North American PRRSV-based modified live vaccine (Ingelvac PRRS MLV; Boehringer Ingelheim Animal Health, St. Joseph, MO) and were artificially inseminated. The sows were randomly divided into three groups. The vaccinated (group 2) and nonvaccinated (group 3) sows developed a PRRSV viremia at 7 to 28 days postinsemination with the European PRRSV-spiked semen. The number of genomic copies of the European PRRSV in serum samples was not significantly different between vaccinated and nonvaccinated sows. All negative-control sows in group 1 farrowed at the expected date. The sows in groups 2 and 3 farrowed between 103 and 110 days after the first insemination. European PRRSV RNA was detected in the lungs of 8 out of 11 live-born piglets and 46 out of 54 stillborn fetuses. In addition, PRRSV RNA was detected using in situ hybridization in other tissues from vaccinated sows that had been inseminated with European PRRSV-spiked semen (group 2). The present study has demonstrated that vaccinating sows with the North American PRRSV-based modified live vaccine does not prevent reproductive failure after insemination with European PRRSV-spiked semen.

Seroprevalence of bovine viral diarrhea virus neutralizing antibodies in finisher hogs in Ontario swine herds and targeted diagnostic testing of 2 suspect herds

A pilot study was initiated to determine the seroprevalence of bovine viral diarrhea virus (BVDV) neutralizing antibodies in finisher hogs in Ontario swine herds, including 2 swine herds with clinical syndromes suspicious of BVDV. No herds were positive for BVDV antibodies by virus neutralization. The 2 swine herds with clinical disease suggestive of pestivirus infection were also negative for antibodies to BVDV in indirect fluorescent antibody assays. Prevalence of BVDV in Ontario swine farms is negligible.

Interleukin-1β expression by a recombinant porcine reproductive and respiratory syndrome virus

The cytokine interleukin-1 beta (IL-1β) is a potent inflammatory mediator in response to infection, and can be used as an immunological adjuvant. In this study, we constructed a recombinant porcine reproductive and respiratory syndrome virus (vP129/swIL1β) expressing swine IL-1β from the separate subgenomic mRNA inserted between the ORF1b and ORF2 genome region. MARC-145 cells infected with vP129/swIL1β secreted 1947 pg of IL-1β per 2 × 10(5)cells at 36 h post-infection. In vitro growth kinetics analysis in MARC-145 cells showed that the vP129/swIL1β virus had a similar replication rate as that of parental virus. We further performed in vivo characterization of the vP129/swIL1β virus in a nursery pig disease model. The vP129/swIL1β infected pigs did not show visible clinical signs, while respiratory distress and lethargy were evident in pigs infected with the parental virus. The expression of various cytokines from peripheral blood mononuclear cells measured by fluorescent microsphere immunoassay showed that IL-1β, IL-4 and IFN-γ expression levels were up-regulated in pigs infected with vP129/swIL1β at 7 and 14 days post-infection. However, no detectable level of IL-1β was found in serum samples from pigs infected with either vP129/swIL1β or parental virus. In summary, this study demonstrated a recombinant PRRSV as a useful tool to study the role of different cytokines in disease progression and immune responses, which represents a new strategy for future therapeutic application and vaccine development.

Effect of modified-live porcine reproductive and respiratory syndrome virus (PRRSv) vaccine on the shedding of wild-type virus from an infected population of growing pigs

There are ongoing efforts to eliminate porcine reproductive and respiratory syndrome virus (PRRSv) from regions in the United States swine industry. However, an important challenge for the accomplishment of those efforts is the re-infection of pig units due to the area spread of PRRSv. The objective of this study was to evaluate the effect of PRRS modified-live virus vaccine (MLV) on viral shedding and on dynamics of PRRSv infection in pig populations raised under commercial conditions. The study composed of two rooms of 1000 pigs each. Ten percent of pigs of each room were inoculated with a field isolate of PRRSv. Rooms had separate air spaces and strict scientifically validated biosecurity protocols were adopted to avoid movement of pathogens between rooms. At 8 and 36 dpi (days post inoculation), all pigs of the challenge-vaccine group were inoculated with a MLV vaccine. Pigs of the challenge-control group were placebo-inoculated. Blood and oral fluid samples were collected from each room at 0, 8, 36, 70, 96 and 118 dpi for PRRSv RNA detection using PCR. PRRSv-antibodies were also screened from blood serum samples with a commercially available ELISA test. Additionally, tonsil scraping samples were collected from both groups at 70, 96 and 118 dpi. Moreover, air samples were collected 6 times per week from 0 to 118 dpi and were tested for PRRSv RNA using qPCR assay. There was no difference in the PRRSv infection dynamics measured as duration and magnitude of viremia and seroconversion. Also, there was no difference in the frequency of tonsil scraping samples PRRSv-positive by PCR. However, the challenge-vaccine group had significantly less PRRSv shed compared to the challenge-control group. The challenge-vaccine group had significant less PRRSv-positive oral fluids at 36 dpi. Moreover, the challenge-vaccine group had significant reduction in the cumulative PRRSv shed in the air.

Experimental co-infection of pigs with Bovine viral diarrhea virus 1 and Porcine circovirus-2

The role of Bovine viral diarrhea virus (BVDV) in the development of Porcine circovirus-2 (PCV-2)-associated disease (PCVAD) was investigated in 2 experimental studies. In the first, separate groups of germ-free pigs were inoculated with filtered tissue homogenate (from diseased pigs) containing PCV-2b + BVDV-1–like virus (group 1), PCV-2a + BVDV-1–like virus (group 4), BVDV-1–like virus only (group 3), or PCV-2b + BVDV-1–like virus following a BVDV vaccination protocol (group 2). This last group was used to test if BVDV vaccination would prevent clinical PCVAD in this model. Many of the inoculated pigs had mild multisystemic inflammation consistent with classic PCVAD. One vaccinated, dually inoculated pig had acute respiratory distress followed by death at 21 days postinfection. Lesions in this pig resembled the severe form of PCVAD observed in the field since the fall of 2004, suggesting a role of ruminant pestiviruses and/or vaccination in the development of this disease. In the second study, cesarean-derived, colostrum-deprived pigs were inoculated with PCV-2b and a cytopathic strain of BVDV-1 (cpBVDV-NADL) either alone or in combination. Clinical signs of PCVAD were seen in a single animal inoculated only with PCV-2b. This pig had growth retardation followed by acute respiratory distress leading to death 30 days postinfection. Pulmonary lesions in this animal were similar to those seen in the pig that died in the first study. Infection with cpBVDV-NADL did not enhance PCV-2b replication or lesion formation.

Effect of the modified live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine on European and North American PRRSV shedding in semen from infected boars

The objective of the present study was to compare the effects of the modified live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine (Ingelvac PRRS MLV; Boehringer Ingelheim Animal Health, St. Joseph, MO) on European and North American PRRSV shedding in the semen of experimentally infected boars. The boars were randomly divided into six groups. Vaccinated boars shed the North American PRRSV at the rate of 10(0.1) to 10(1.0) viral genome copies per ml and 3.63 to 10(1.1) 50% tissue culture infective doses (TCID(50))/ml, respectively, in semen, whereas nonvaccinated boars shed the North American PRRSV at the rate of 10(0.2) to 10(4.7) viral genome copies per ml and 1.14 to 10(3.07) TCID(50)/ml, respectively, in semen. Vaccinated boars shed the European PRRSV at the rate of 10(0.1) to 10(4.57) viral genome copies per ml and 1.66 to 10(3.10) TCID(50)/ml, respectively, in semen, whereas nonvaccinated boars shed the European PRRSV at the rate of 10(0.3) to 10(5.14) viral genome copies per ml and 1.69 to 10(3.17) TCID(50)/ml, respectively, in semen. The number of genomic copies of the European PRRSV in semen samples was not significantly different between vaccinated and nonvaccinated challenged European PRRSV boars. The present study demonstrated that boar vaccination using commercial modified live PRRSV vaccine was able to decrease subsequent shedding of North American PRRSV in semen after challenge but was unable to decrease shedding of European PRRSV in semen after challenge.

Microbiological identification and analysis of swine tonsils collected from carcasses at slaughter

The primary objective of this 7-month study was to determine the prevalence of porcine pathogens of the tonsil of the soft palate of swine at slaughter. Additional objectives were to determine if sampling the carcasses of normal or abnormal hogs provided different microbiological profiles and if the slaughter plant provides a feasible sampling frame and environment for detecting and monitoring important pathogens in tonsils that have health implications for both swine and humans. A total of 395 samples were collected from 264 farms. Of these, 180 tonsils were collected from normal carcasses and 215 tonsils were collected from carcasses that were diverted to the hold rail. Laboratory testing included bacteriological culture and identification as well as real time-polymerase chain reaction (PCR) testing for porcine reproductive and respiratory syndrome virus (PPRSV) and immunohistochemistry (IHC) for porcine circovirus-2 (PCV-2). The most commonly isolated bacteria included: Streptococcus suis (53.7%), Arcanobacterium pyogenes (29.9%), Pasteurella multocida (27.3%), and Streptococcus porcinus (19.5%). Virus screening revealed evidence of PRRSV and PCV-2 in 22.0% and 11.9% of the samples, respectively. Salmonella Typhimurium and Yersinia enterocolitica were isolated in 0.5% and 1.8% of the samples, respectively. Tonsils collected from the hold rail were more likely to be positive for Staphylococcus hyicus [odds ratio (OR) = 7.51, confidence interval (CI) = 2.89 to 19.54], Streptococcus porcinus (OR = 9.93, CI = 4.27 to 23.10), and Streptococcus suis (OR = 2.16, CI = 1.45 to 3.24). Tonsils collected from abnormal carcasses were less likely to be positive for Staphylococcus aureus (OR = 0.05, CI = 0.005 to 0.482).

Interleukin-8, interleukin-1beta, and interferon-gamma levels are linked to PRRS virus clearance

Infection with porcine reproductive and respiratory syndrome virus (PRRSV) results in a weak antiviral immune response that leads to a persistent infection in a subset of pigs. We investigated the intensity and timing of the early cytokine responses to PRRSV infection to determine their utility as a predictor of persistence. As part of the "Big Pig" project, we evaluated cytokine gene expression in lymphoid tissues collected from pigs for up 202 days post-infection (dpi); serum samples were collected biweekly. Cytokine mRNA levels were compared between pigs that cleared the viral infection from serum and tissues (non-persistent [NP] pigs) to those of persistent (P) pigs, that had viral RNA in their serum for up to 126 dpi. The gene expression studies in the tracheobronchial lymph nodes (TBLN) of all the pigs showed upregulation of interferon-gamma (IFN-gamma)-associated T-helper 1 (Th-1) markers from 14-84 dpi, and of T-regulatory interleukin-10 (IL-10), but no upregulation of innate markers (IFN-A, IL-1B, and IL-8). At later time points (>112 dpi) these genes were no longer differentially expressed and thus were uninformative for persistence studies. Statistical analyses of serum cytokine levels indicated that innate cytokine (IL-1beta and IL-8) levels were upregulated early after infection. Interestingly, serum IL-8 levels in NP pigs were significantly higher than in P pigs at 14 dpi. When analyzed together, variations in all three of the serum cytokines tested (IL-8, IL-1beta, and IFN-gamma) was significantly correlated with virus level, accounting for approximately 84% of the variations observed. These results indicate that while each cytokine individually has minor effects on the length of virus replication, the combination of cytokine activities should be considered when understanding the role of immunity in persistence.

Porcine reproductive and respiratory syndrome virus (PRRSV) in serum and oral fluid samples from individual boars: will oral fluid replace serum for PRRSV surveillance?

The purpose of this study was to determine whether oral fluid samples could be used to monitor individually-housed adult boars for porcine reproductive and respiratory syndrome virus (PRRSV) infection. In 3 trials, 24 boars were intramuscularly (IM) inoculated with a modified-live PRRSV (MLV) vaccine (Trial 1), a Type 1 PRRSV isolate (Trial 2), or a Type 2 isolate (Trial 3). Oral fluid samples were collected daily and serum samples were collected twice weekly. Following the completion of the study, samples were randomized and blind-tested for PRRSV by real-time quantitative reverse-transcription polymerase chain reaction (qRT-PCR). PRRSV was detected in oral fluids at DPI 1 and all oral fluid specimens were PRRSV qRT-PCR positive at DPI 4. Although PRRSV was detected in both serum and oral fluid specimens through DPI 21, a comparison of matched samples from individual boars showed that oral fluid was equal to serum for the detection of PRRSV at DPI 7 and more likely to be positive than serum on DPI 14 and 21. Overall, oral fluid was superior to serum for the detection of PRRSV using PCR over the 21-day observation period in this study. The results of this experiment suggest that individually-penned oral fluid sampling could be an efficient, cost-effective approach to PRRSV surveillance in boar studs and other swine populations.

Vascular lesions in pigs experimentally infected with porcine circovirus type 2 serogroup B

Vasculitis is a hallmark lesion of the severe form of systemic porcine circovirus-associated disease (PCVAD). In 2 experimental studies with porcine circovirus type 2 serogroup b (PCV2b), 2 pigs developed fatal PCVAD with acute vasculitis, and 5 related pigs developed chronic lymphohistiocytic and plasmacytic peri- and endarteritis. Five of these pigs (1 with acute vasculitis and 4 with chronic vasculitis) had also been inoculated with bovine viral diarrhea virus type 1 (BVDV1) or BVDV1-like virus. Vascular lesions were similar, independent of whether pigs had been inoculated singly with PCV2b or dually with PCV2b and BVDV1 or BVDV1-like virus. The acute vasculitis was accompanied by marked pulmonary and mesenteric edema and pleural effusion. In situ hybridization demonstrated abundant intracytoplasmic porcine circovirus type 2 (PCV2) nucleic acid in endothelial, smooth muscle-like, and inflammatory cells within and around affected arteries. The pigs with lymphohistiocytic and plasmacytic vasculitis had lesions of systemic PCVAD, including multisystemic lymphoplasmacytic and histiocytic or granulomatous inflammation. PCV2 nucleic acid was detected in renal tubule epithelial cells, mononuclear inflammatory cells, and rare endothelial cells in noninflamed vessels in multiple tissues of these animals. The 2 pigs with acute vasculitis had no PCV2-specific antibodies (or a low titer of), whereas the pigs with lymphohistiocytic and plasmacytic vasculitis developed high antibody titers against this virus. These observations suggest that (1) acute vasculitis observed in the current studies is directly caused by PCV2b, (2) chronic vasculitis may in part be mediated by the subsequent immune response, and (3) host factors and viral strain may both contribute to vasculitis in animals infected with PCV2b.

Expression of inflammatory cytokines and Toll-like receptors in the brain and respiratory tract of pigs infected with porcine reproductive and respiratory syndrome virus

The objective of this experiment was to evaluate the central and peripheral expression of selected pro-inflammatory cytokines and Toll-like receptors (TLRs) in pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV). Twenty-four 8-week-old pigs were inoculated with either sterile medium or PRRSV. Pigs were monitored 14d after inoculation and then euthanized for tissue sample collection. PRRSV was detected in serum, lung and brain tissue of pigs given PRRSV but not in any tissue of pigs given medium. Infection with PRRSV increased serum levels of IL-1beta, IL-6, TNFalpha, and IFNgamma and elicited a mild transient fever and reduced growth performance. Infection by PRRSV also increased mRNA for the pro-inflammatory cytokines as well as mRNA for TLR3, TLR4, and TLR7 in the tracheobronchial lymph nodes. The TLR3, TLR4, TLR7 and most of the pro-inflammatory genes also were up-regulated in discrete brain areas of PRRSV-infected pigs. Collectively, the results indicate that following inoculation, PRRSV is present in the periphery and brain and that infection is associated with a peripheral and central pro-inflammatory response, fever, and reduced growth performance. The findings are interpreted to suggest the innate immune system of the brain is responsive to PRRSV infection.