Jiwoon Jeong

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

ABSTRACT 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.

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 two genetically distant type 2 porcine reproductive and respiratory syndrome virus (PRRSV) modified live vaccines against Vietnamese highly pathogenic PRRSV.

Highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) known as pig high fever disease was first reported in China and has spread rapidly in neighboring southeastern Asian countries. The objective of this study was to evaluate the efficacy of a new type 2 PRRSV modified live vaccine (vaccine A) against a challenge with a HP-PRRSV and to compare the efficacy of two genetically distant type 2 PRRSV modified vaccines (vaccine A for lineage 8 and vaccine B for lineage 5) against HP-PRRSV (lineage 8) challenge. Pigs were divided into 4 groups (n=12/group); vaccinated challenged (2 groups), unvaccinated challenged, and unvaccinated unchallenged groups. Regardless of vaccines, vaccinated challenged pigs showed significantly lower (P<0.05) mean rectal temperatures and respiratory scores, levels of HP-PRRSV viremia, and lung lesions and HP-PRRSV antigens within lung lesions compared to unvaccinated challenged pigs. Vaccinated challenged pigs had significantly higher (P<0.05) numbers of interferon-γ secreting cells (IFN-γ-SC) compared to unvaccinated challenged pigs. Significant differences were also found when comparing two type 2 PRRSV vaccines after HP-PRRSV challenge. The use of type 2 PRRSV vaccine A was able to significantly reduce fever when compared to type 2 PRRSV vaccine B in vaccinated challenged pigs. Vaccination of pigs with vaccine A reduced viral loads in their blood and induced higher numbers of HP-PRRSV-specific IFN-γ-SC than vaccination of pigs with vaccine B. This study demonstrates partial protection of two genetically distant type 2 PRRSV vaccines against HP-PRRSV challenge in growing pigs.

A New Modified Live Porcine Reproductive and Respiratory Syndrome Vaccine Improves Growth Performance in Pigs under Field Conditions

ABSTRACT 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 Koreas 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 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.

Evaluation of a 20 year old porcine reproductive and respiratory syndrome (PRRS) modified live vaccine (Ingelvac® PRRS MLV) against two recent type 2 PRRS virus isolates in South Korea

Type 2 porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) was first isolated in Korea in 1994. The commercial PRRS modified live vaccine (Ingelvac(®) PRRS MLV, Boehringer Ingelheim Vetmedica Inc., St. Joseph, Missouri, USA) based on type 2 PRRSV, was first licensed for use in 3- to 18-week-old pigs in Korea in 1996. The objective of the present study was to evaluate the efficacy of this 20year old commercial PRRS modified live vaccine (MLV) against two recent PRRSV isolates. Two genetically distant type 2 PRRSV strains (SNUVR150004 for lineage 1 and SNUVR150324 for lineage 5), isolated in 2015, were used as challenge virus. Regardless of the challenge virus, vaccination of pigs effectively reduced the level of viremia, the lung lesions, and of the PRRSV antigen within the lung lesions. The induction of virus-specific interferon-γ secreting cells by the PRRS vaccine produced a protective immune response, leading to the reduction of PRRSV viremia. There were no significant differences in efficacy against the two recently isolated viruses by the PRRS MLV based on virological results, immunological responses, and pathological outcomes. This study demonstrates that the PRRS MLV used in this study is still effective against recently isolated heterologous type 2 PRRSV strains even after 20 years of use in over 35 million 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.

Concurrent vaccination of pigs with type 1 and type 2 porcine reproductive and respiratory syndrome virus (PRRSV) protects against type 1 PRRSV but not against type 2 PRRSV on dually challenged pigs.

The objective of the present study was to evaluate the effect of concurrent vaccination of pigs with both type 1 and type 2 porcine reproductive and respiratory syndrome virus (PRRSV) vaccine against heterologous dual challenge of both genotypes and compare with single vaccination of pigs against heterologous single challenge of both genotypes. Pigs were administered both type 1 and type 2 PRRSV vaccine concurrently into separate anatomical sites at 28 days of age and inoculated intranasally with both genotypes at 63 days of age. Neutralizing antibodies (NA) were not detected in any pigs in any group (NA titer <2 log2) throughout the experiment. In addition, concurrent vaccination of pigs with two PRRSV genotypes had significantly lower numbers of type 1 and type 2 PRRSV-specific interferon-γ secreting cells (IFN-γ-SC) compared to vaccination of pigs with type 1 or type 2 PRRSV only. Despite the decreased induction of type 1 PRRSV-specific IFN-γ-SC, concurrent vaccination is still able to reduce type 1 PRRSV viremia whereas the decreased induction of type 2 PRRSV-specific IFN-γ-SC by concurrent vaccination correlates with lack of reduction of type 2 PRRSV viremia after dual challenge. The results of this study demonstrated that concurrent vaccination of pigs with two PRRSV genotypes is able to reduce the levels of type 1 PRRSV viremia and lung lesions but not able to reduce the levels of type 2 PRRSV viremia and lung lesions.

Comparison of protection provided by type 1 and type 2 porcine reproductive and respiratory syndrome field viruses against homologous and heterologous challenge

The objective of this study was to compare protection provided by type 1 and type 2 porcine reproductive and respiratory syndrome virus (PRRSV) against homologous and heterologous challenge based on clinical, virological, immunological, and pathological analysis. At 3 and 8 weeks of age, pigs were inoculated intranasally with either 3mL of tissue culture fluid containing 10(5) TCID50/mL of type 1 PRRSV or 3mL of tissue culture fluid containing 10(5) TCID50/mL of type 2 PRRSV. The homologous challenges resulted in a significant boost of the neutralizing antibodies (NA) and interferon-γ secreting cells (IFN-γ-SC) compared to heterologous challenges. The reduction of secondary challenging PRRSV viremia coincided with the appearance of homologous PRRSV-specific NA and IFN-γ-SC. Homologous challenge reduced the severity of lung lesions and levels of PRRSV viremia significantly in pigs in comparison with heterologous challenge. The differences in homologous and heterologous NA and IFN-γ-SC response may explain the differences in protection against homologous and heterologous challenge between type 1 and type 2 PRRSV. Primary challenge (immunization) with type 1 PRRSV provided protection against the secondary homologous challenge with type 1 PRRSV but failed to provide protection against the secondary heterologous challenge of type 2 PRRSV. Primary challenge with type 2 PRRSV provided protection against both the secondary homologous challenge with type 2 PRRSV and the secondary heterologous challenge with type 1 PRRSV.

Vaccination with a porcine reproductive and respiratory syndrome virus vaccine at 1-day-old improved growth performance of piglets under field conditions

A porcine reproductive and respiratory syndrome virus (PRRSV) modified live-virus (MLV) vaccine was evaluated under field conditions for registration as recommended by the Republic of Koreas Animal, Plant & Fisheries Quarantine & Inspection Agency. A single dose of the vaccine was administered to 1-day-old piglets and their growth performance was monitored under field conditions. Three separate farms were selected based on their history of PRRSV-associated respiratory diseases. On each farm, 40 pigs were randomly allocated to one of two treatment groups: (i) vaccinated (n = 20) and (ii) unvaccinated (n = 20) pigs at 1 day of age. Vaccinated pigs showed an increase of their market weight of 6.23 kg/pig compared to the unvaccinated pigs (98.01 kg in vaccinated group vs. 91.78 kg in unvaccinated group; P < 0.05) and exhibited a decrease in mortality rate by 6.7% (3.3% in vaccinated group vs. 10% in unvaccinated group; P < 0.05). The pigs had a sufficiently mature immune system for the vaccine to elicit humoral and cell-mediated immunity (as measured by anti-PRRSV antibodies and PRRSV-specific interferon-γ secreting cells, respectively) at 1 day of age even in the presence of maternally derived antibodies. The results presented in this study demonstrate that the PRRSV MLV vaccine is effective in improving growth performance from day 1 all the way to day 182 in endemic farms suffering with PRRSV-2 infection or both PRRSV-1 and PRRSV-2 infection.