The porcine reproductive and respiratory syndrome virus (PRRSV) can cause reproductive barriers in breeding pigs and respiratory symptoms in piglets. In this review, we summarize research progress of the infection and replication mechanisms of the PRRSV. We also review the virulence determinants of the PRRSV. All these fundamental studies are important for the control and elimination of the PRRSV.
Animals ; Porcine Reproductive and Respiratory Syndrome ; virology ; Porcine respiratory and reproductive syndrome virus ; genetics ; pathogenicity ; physiology ; Swine ; Virulence ; Virus Replication

To develop an attenuated vaccine against the highly pathogenic porcine reproductive and respiratory syndrome (HP-PRRS) virus, the HP-PRRS virus strain TJ was attenuated by serial passages and plaque cloned every 5 to 10 passages in Marc-145 cells. Genetic variation and pathogenicity of HP-PRRSV strain TJ in the course of attenuation were analyzed. The results showed that the strain TJ sustained various sequence changes during the course of attenuation. Fifty-eight amino acids changes and a new continuous 120 amino acids deletion after the discontinuous 30 amino acids deletion (sites 481 and 533-561) occurred in strain TJ passages 140, and the position of 120 amino acids deletion was between 628 to 747 according to VR-2332. Animal test showed that the pathogenicity of strain TJ passages 20 was attenuated obviously, so we presume that genetic variation in nonstructural protein nsp2-nsp5, nsp7 and structural protein GP5 during the attenuation provides the molecular bases for the observed attenuated phenotype.
Amino Acid Sequence ; Animals ; Genetic Variation ; Molecular Sequence Data ; Porcine Reproductive and Respiratory Syndrome ; virology ; Porcine respiratory and reproductive syndrome virus ; classification ; genetics ; isolation & purification ; pathogenicity ; Sequence Deletion ; Serial Passage ; Swine ; Vaccines, Attenuated ; genetics ; isolation & purification ; Virulence

Animals ; Genome, Viral ; Porcine respiratory and reproductive syndrome virus ; genetics ; pathogenicity ; Swine ; Viral Nonstructural Proteins ; genetics ; physiology ; Viral Structural Proteins ; genetics ; physiology ; Virulence ; genetics

Epidemiological characteristics of swine pulmonary Pneumocystis (P.) carinii and concurrent infections were surveyed on Jeju Island, Korea, within a designated period in 172 pigs submitted from 54 farms to the Department of Veterinary Medicine, Jeju National University. The submitted cases were evaluated by histopathology, immunohistochemistry, PCR/RT-PCR, and bacteriology. P. carinii infection was confirmed in 39 (22.7%) of the 172 pigs. Histopathologically, the lungs had moderate to severe lymphohistioctyic interstitial pneumonia with variable numbers of fungal organisms within lesions. Furthermore, porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV-2) co-infection was a common phenomenon (12.8%, 20.5%, and 48.7% were positive for PRRS, PCV-2, or both, respectively, as determined by PCR/RT-PCR). Infection was much more concentrated during winter (December to March) and 53.8% of the infected pigs were 7- to 8-weeks old. In addition, three pigs showed co-infection with bacteria such as Pasteurella multocida and Streptococcus suis. The results of the present study suggest that the secondary P. carinii infection is common following primary viral infection in swine in Korea. They further suggest that co-infection of P. carinii might be enhanced by the virulence of primary pathogens or might have synergistic effects in the pigs with chronic wasting diseases.
Aging ; Animals ; *Circovirus/pathogenicity ; Incidence ; Pasteurella Infections/complications/epidemiology/veterinary ; Pasteurella multocida/i ; *Pneumocystis carinii/immunology/pathogenicity ; Pneumonia, Pneumocystis/complications/epidemiology/physiopathology/*veterinary ; Porcine Postweaning Multisystemic Wasting Syndrome/complications/*epidemiology ; Porcine Reproductive and Respiratory Syndrome/*epidemiology ; *Porcine respiratory and reproductive syndrome virus/pathogenicity ; Prevalence ; Republic of Korea/epidemiology ; Reverse Transcriptase Polymerase Chain Reaction ; Sea ; Streptococcal Infections/complications/epidemiology/veterinary ; Streptococcus suis/i ; Sus scrofa ; Swine Diseases/epidemiology/virology