Submitted to: International Union of Microbiological Societies Proceedings/Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2005
Publication Date: 7/23/2005
Citation: Vincent, A.L., Lekcharoensuk, P., Ma, W., Gramer, M., Richt, J.A., Lager, K.M. 2005. Evaluation of North American hemagglutinin subtype 1 swine influenza isolates [abstract]. International Congress of Virology. p. 44. Interpretive Summary:
Technical Abstract: In general, swine influenza viruses (SIV) of the hemagglutinin subtype 1 (H1) isolated in North America have not been well characterized in the swine host. An apparent shift in the rate of mutation and reassortment has occurred in SIV during the latter part of the twentieth century, including viruses within the H1 subtype. Two independent animal studies were done to evaluate and compare the pathogenesis of 10 SIV isolates dating from 1930 to currently active isolates. Isolates included in replicate 1 were A/Swine/Iowa/15/30 H1N1, A/Swine/MN/1192/2001 H1N2, A/Swine/NC36883/02 rH1N1, and field isolates from the Minnesota Veterinary Diagnostic Lab, including a 2003 H1N2, a 2004 H1N2, and a 2004 rH1N1. Isolates included in replicate 2 were A/Swine/Iowa/15/30 H1N1, IA 1945 H1N1, A/Swine/WIS/1/1968 H1N1, IA 1973 H1N1, and A/Swine/MN/37866/1999 H1N1. The HA and NA genes of each isolate were sequenced for genetic comparison. Pigs were challenged at 4 weeks of age and euthanized at 5 dpi. Rectal temperatures were taken daily from -2 dpi to 5 dpi. Nasal swabs were taken on 0, 3, and 5 dpi for virus isolation. At necropsy, lungs were evaluated for pneumonia and lavaged to obtain bronchioalveolar lavage fluid (BAL) for titration. Statistically significant differences in percentage of pneumonia and virus titers were detected between isolates, with recent isolates tending to produce more severe disease, have more nasal shedding and higher virus titers in the lung. However, shedding and virus titers were not always correlated with lesions or rectal temperatures. In general there was less pneumonia, shedding and lower titers with the 1930 and 1945 viruses as compared to other isolates. Based on the limited number of isolates evaluated, it appears that swine isolates since 1945 have increased in virulence as measured by pneumonia, viral replication and shedding. Genetic analysis revealed high variability among the H1 isolates, although there was little apparent correlation between genetic relatedness and pathogenicity.