Pathology and Virus Distribution in the Lung and Lymphoid Tissues of Pigs Experimentally Inoculated with Three Distinct Type 1 PRRS Virus Isolates of Varying Pathogenicity.
Porcine reproductive and respiratory syndrome (PRRS) continues to be the most economically important disease of swine worldwide. The appearance of highly pathogenic PRRS virus (PRRSV) strains in Europe and Asia has raised concerns about this disease and initiated increased efforts to understand the pathogenesis. In this study, we have compared the pathology and the virus distribution in tissues of pigs experimentally inoculated with three different genotype 1 PRRSV isolates. Sixty 5-week-old pigs were inoculated intranasally with a) the Lelystad virus (LV), b) a field strain from the UK causing respiratory clinical signs (UK) or c) a highly pathogenic strain from Belarus (BE). Sixteen animals were mock-infected and used as controls. The animals were euthanized at 3, 7 and 35 days post-infection (dpi), and lung and lymphoid tissues collected for histopathological examination and PRRSV detection by immunohistochemistry (IHC). Histopathological lesions consisted of interstitial pneumonia with mononuclear cell infiltrates in the lungs, lymphoid depletion, apoptosis and follicular hyperplasia in the spleen, lymph nodes and tonsil and lymphoid depletion in the thymus. Porcine reproductive and respiratory syndrome virus was detected mainly in monocytes-macrophages. BE-infected animals showed the highest pathological scores and the highest presence of virus at 3 and 7 dpi, followed by the UK field strain and then LV. Moderate lesions were observed at 35 dpi with lesser detection of PRRSV by IHC in each infected group. The highly pathogenic BE strain induced more severe pathology in both lungs and lymphoid organs of pigs compared with the classic field isolate and the prototype LV. The increased severity of pathology was in correlation with the presence of a higher number of PRRSV-infected cells in the tissues.
Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, UK.|Department of Microbial and Cellular Sciences, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK.
S B
SB
Morgan
Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, UK.
J P
JP
Frossard
Department of Anatomy and Comparative Pathology, Faculty of Veterinary Medicine, Murcia University, Murcia, Spain.|Department of Pathology, Animal Health and Veterinary Laboratories Agency, Addlestone, UK.
F J
FJ
Pallares
Department of Pathology, Animal Health and Veterinary Laboratories Agency, Addlestone, UK.
J
J
Gough
Faculty of Veterinary Medicine, Warsaw University of Life Sciences, Warsaw, Poland.
T
T
Stadejek
Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, UK.
S P
SP
Graham
Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, UK.
F
F
Steinbach
Virology Department, Animal Health and Veterinary Laboratories Agency, Addlestone, UK.
T W
TW
Drew
Department of Pathology, Animal Health and Veterinary Laboratories Agency, Addlestone, UK.|School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK.
F J
FJ
Salguero
D000818:Animals; D008168:Lung / Q000821:virology; D008221:Lymphoid Tissue / Q000821:virology; D008297:Male; D016366:Open Reading Frames; D010802:Phylogeny; D019318:Porcine Reproductive and Respiratory Syndrome / Q000473:pathology* / Q000821:virology; D019316:Porcine respiratory and reproductive syndrome virus / Q000472:pathogenicity* / Q000502:physiology*; D002094:Republic of Belarus; D013552:Swine; D006113:United Kingdom; D014774:Virulence
apoptosis; histopathology; immunohistochemistry; porcine reproductive and respiratory syndrome virus