Biological responses to porcine respiratory and reproductive syndrome virus in pigs of two genetic populations

• Published in: Journal of animal science Vol. 83; no. 7; pp. 1494 - 1502
• Main Authors: Petry, D. B, Holl, J. W, Weber, J. S, Doster, A. R, Osorio, F. A, Johnson, R. K
• Format: Journal Article
• Language: English
• Published: Savoy, IL Am Soc Animal Sci 01-07-2005; American Society of Animal Science
• Subjects: Animal productions; Animals; antibodies; Biological and medical sciences; Body Temperature; body weight; disease course; disease resistance; Enzyme-Linked Immunosorbent Assay - veterinary; Female; Fundamental and applied biological sciences. Psychology; genetic variation; Genetic Variation - immunology; genotype; Litter Size - genetics; Lung - pathology; Lung - virology; lungs; lymph nodes; Lymph Nodes - virology; Male; porcine reproductive and respiratory syndrome; Porcine Reproductive and Respiratory Syndrome - genetics; Porcine Reproductive and Respiratory Syndrome - immunology; Porcine Reproductive and Respiratory Syndrome - virology; Porcine reproductive and respiratory syndrome virus; Porcine respiratory and reproductive syndrome virus; Porcine respiratory and reproductive syndrome virus - immunology; Random Allocation; Statistics as Topic; Swine; Terrestrial animal productions; Vertebrates; viremia; Viremia - veterinary; Viremia - virology; Weight Gain; Farming animal; Arterivirus; Variations; Biological indicator; Population genetics; Pig; Virus; Genetic Variation; Vertebrata; Meat animals; Mammalia; Arteriviridae; Swine infertility respiratory syndrome virus; Artiodactyla; Biological Indicators; Nidovirales; Ungulata
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/2005.8371494x

One hundred pigs from the NE Index Line (NEI) and 100 Hampshire-Duroc cross pigs (HD) were inoculated intranasally with porcine respiratory and reproductive syndrome virus (PRRSV 97-7895 strain) at 26 d of age to determine whether genetic variation in response to PRRSV exists. An uninfected littermate to each infected pig served as a control. Pigs were from 163 dams and 83 sires. Body weight and rectal temperature were recorded, and blood samples were drawn from each pig on d 0 before inoculation and on d 4, 7, and 14 after inoculation. Pigs were sacrificed on d 14. Lung and bronchial lymph nodes were collected, placed in optimal cutting temperature compound, and frozen at -80°C. The presence of PRRSV in serum and in lung tissue and bronchial lymph nodes was determined by isolation in cell culture. The presence of antibodies in serum collected on d 14 was determined by a commercial ELISA test. Lung tissue was examined microscopically and scored for incidence and severity of lesions (score of 1 to 3; 1 = no or few lesions, and 3 = severe interstitial pneumonia). Data were analyzed with a mixed model that included random sire and dam effects. The interaction of line x treatment was significant (P < 0.001) for weight change and rectal temperature. Un-infected HD pigs gained 0.67 kg more from d 0 to 14 and averaged 0.32°C higher rectal temperature than uninfected NEI pigs (P < 0.001), whereas infected NEI pigs gained 0.34 kg more and had -0.54°C lower temperature than infected HD pigs (P < 0.001). Viremic titer (cell culture infectious dose 50%/mL) was greater (P < 0.05) in HD than NEI at d 4 (10[superscript 4.52] vs. 10[superscript 4.22]), 7 (10[superscript 4.47] vs. 10[superscript 3.99]), and 14 (10[superscript 3.49] vs. 10[superscript 3.23]). Viral titer loads in lung (P = 0.11) and bronchial lymph nodes tended (P = 0.07) to be greater in HD than NEI pigs. Antibody signal-to-positive (S/P) ELISA ratios in infected pigs ranged from 0.18 to 3.38, and 88% had levels [>/=]0.40, which is the positive threshold for this ELISA. The S/P range in uninfected pigs was 0 to 1.11, and 99% had levels </=0.40. Mean S/P ratio for infected pigs was 0.23 units higher in HD than in NEI (P < 0.001). The HD pigs had a greater incidence of interstitial pneumonia and 0.65 higher mean lesion scores than NEI pigs (P < 0.001). In summary, responses of pigs of the two lines to infection with PRRSV differed, indicating that underlying genetic variation existed.