Ikjae Kang

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 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 manufacturers 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.

Comparative efficacy of commercial Mycoplasma hyopneumoniae and porcine circovirus 2 (PCV2) vaccines in pigs experimentally infected with M. hyopneumoniae and PCV2.

The efficacies of two commercial Mycoplasma hyopneumoniae bacterins and porcine circovirus 2 (PCV2) vaccines were compared in conventional pigs immunized at different ages based on humoral response, pathological observation, and growth performance from birth to finishing (175 days of age) using a M. hyopneumoniae and PCV2 co-infection challenge model. One-week-old pigs (n=110) were randomly assigned to five groups: three vaccinated and challenged (VC), and one each of non-vaccinated and challenged (NVC) and negative control. A significant difference was found in the number of genomic copies of M. hyopneumoniae in nasal swabs and PCV2 in serum samples, the average daily weight gain (gram/pig/day) between 63 and 133 dpi, gross and histopathological lung lesion scores, histopathological lymph node lesion scores, and the immunohistochemical analysis of PCV2 among the three VC groups. The single dose schedule for M. hyopneumoniae bacterins and PCV2 vaccines have the advantages of (i) improving daily weight gain (122.4%) and slaughter weight (120.5%), and (ii) reducing the incidence of clinical signs and lung and lymph node lesions.

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

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.

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

ABSTRACT 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 100.1 to 101.0 viral genome copies per ml and 3.63 to 101.1 50% tissue culture infective doses (TCID50)/ml, respectively, in semen, whereas nonvaccinated boars shed the North American PRRSV at the rate of 100.2 to 104.7 viral genome copies per ml and 1.14 to 103.07 TCID50/ml, respectively, in semen. Vaccinated boars shed the European PRRSV at the rate of 100.1 to 104.57 viral genome copies per ml and 1.66 to 103.10 TCID50/ml, respectively, in semen, whereas nonvaccinated boars shed the European PRRSV at the rate of 100.3 to 105.14 viral genome copies per ml and 1.69 to 103.17 TCID50/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.

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.

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.

Comparative virulence of reproductive diseases caused by type 1 (European-like) and type 2 (North American-like) porcine reproductive and respiratory syndrome virus in experimentally infected pregnant gilts.

The aim of this study was to compare the virulence of type 1 and type 2 porcine reproductive and respiratory syndrome virus (PRRSV) as assessed by the level of viral replication, viral distribution and apoptosis in stillborn fetuses and live-born piglets from infected pregnant gilts. Type 1 or type 2 PRRSV was given intranasally to pregnant gilts at 3 weeks before the expected date of parturition. Regardless of virus genotype, PRRSV-infected gilts farrowed between 102 and 109 days of gestation, while control uninfected gilts carried the pregnancy to term and farrowed at 114-115 days of gestation. There were no significant differences in the mean number of virus-infected cells per unit area of tissue when type 1 and type 2 virus infections were compared between stillborn fetuses and live-born piglets. Stillborn fetuses from the type 1 PRRSV-infected pregnant gilts had a significantly higher mean number of apoptotic cells per unit area of thymus (P = 0.013) than those from type 2 PRRSV-infected pregnant gilts. Significant differences in virulence were not observed between types 1 and 2 PRRSV in terms of female reproductive failure, although thymic apoptosis differed in stillborn fetuses from type 1 and type 2 PRRSV-infected pregnant gilts.

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

ABSTRACT 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.

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.