title: Comparison of the pathogenicity of two US porcine reproductive and respiratory syndrome virus isolates with that of the Lelystad virus.
abstract: The Lelystad virus or one of two US isolates (VR2385, VR2431) of porcine reproductive and respiratory syndrome virus were given intranasally to 25 4-week-old cesarian-derived colostrum-deprived pigs. Pigs from these groups were necropsied at 1, 2, 3, 5, 7, 10, 15, 21, or 28 days postinoculation. The Lelystad virus and VR2431 induced mild transient pyrexia, dyspnea, and tachypnea. VR2385 induced labored and rapid abdominal respiration, pyrexia, lethargy, anorexia, and patchy dermal cyanosis. All three isolates induced multifocal tan-mottled consolidation involving 6.8% (n = 9; SEM = 3.4) of the lung for Lelystad, 9.7% (n = 9, SEM = 2.7) of the lung for VR2431, and 54.2% (n = 9, SEM = 4.4) of the lung for VR2385 at 10 days postinoculation. Characteristic microscopic lung lesions consisted of type 2 pneumocyte hypertrophy and hyperplasia, necrotic debris and increased mixed inflammatory cells in alveolar spaces, and alveolar septal infiltration with mononuclear cells. Lymphadenopathy with follicular hypertrophy, hyperplasia, and necrosis was consistently seen. Similar follicular lesions were also seen in Peyer's patches and tonsils. Lymphohistiocytic myocarditis and encephalitis were reproduced with all three isolates. Clinical respiratory disease and gross and microscopic lung lesion scores were considerably and significantly more severe in the VR2385-inoculated pigs. All three viruses were readily isolated from sera, lungs, and tonsils throughout the 28 days of the study. The lymphoid and respiratory systems have the most remarkable lesions and appear to be the major site of replication of these viruses. This work demonstrated a marked difference in pathogenicity of porcine reproductive and respiratory syndrome isolates.
authors.affiliation: Veterinary Diagnostic Laboratory, Iowa State University, Ames, USA.
authors.forename: P G
authors.initials: PG
authors.lastname: Halbur
authors.forename: P S
authors.initials: PS
authors.lastname: Paul
authors.forename: M L
authors.initials: ML
authors.lastname: Frey
authors.forename: J
authors.initials: J
authors.lastname: Landgraf
authors.forename: K
authors.initials: K
authors.lastname: Eernisse
authors.forename: X J
authors.initials: XJ
authors.lastname: Meng
authors.forename: M A
authors.initials: MA
authors.lastname: Lum
authors.forename: J J
authors.initials: JJ
authors.lastname: Andrews
authors.forename: J A
authors.initials: JA
authors.lastname: Rathje
mesh_terms: D000311:Adrenal Glands / Q000473:pathology / Q000821:virology; D000818:Animals; D018018:Arterivirus / Q000302:isolation & purification / Q000472:pathogenicity* / Q000502:physiology; D018174:Arterivirus Infections / Q000662:veterinary* / Q000821:virology; D001921:Brain / Q000473:pathology / Q000821:virology; D004195:Disease Models, Animal; D004417:Dyspnea / Q000209:etiology / Q000662:veterinary; D004660:Encephalitis / Q000209:etiology / Q000662:veterinary; D005260:Female; D005334:Fever / Q000209:etiology / Q000662:veterinary; D019084:Fluorescent Antibody Technique, Indirect / Q000662:veterinary; D006321:Heart / Q000821:virology; D007421:Intestine, Small / Q000473:pathology / Q000821:virology; D008168:Lung / Q000473:pathology / Q000821:virology; D008171:Lung Diseases / Q000209:etiology / Q000662:veterinary; D008198:Lymph Nodes / Q000473:pathology / Q000821:virology; D009206:Myocardium / Q000473:pathology; D014066:Palatine Tonsil / Q000473:pathology / Q000821:virology; D013154:Spleen / Q000473:pathology / Q000821:virology; D013552:Swine; D013553:Swine Diseases / Q000821:virology*; D014420:Turbinates / Q000473:pathology