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Virulence, transmission, and heterologous protection of four isolates of Haemophilus parasuis

Susan L. Brockmeier, Crystal L. Loving, Michael A. Mullins, Karen B. Register, Tracy L. Nicholson, Barry S. Wiseman, Rodney B. Baker, Marcus E. Kehrli Jr.
Clinical and diagnostic laboratory immunology 2013 v.20 no.9 pp. 1466-1472
Haemophilus parasuis, animal models, arthritis, disease transmission, live vaccines, meningitis, strains, swine, vaccination, virulence
Haemophilus parasuis causes Glässer's disease, a syndrome of polyserositis, meningitis, and arthritis in swine. Previous studies with H. parasuis have revealed virulence disparity among isolates and inconsistent heterologous protection. In this study, virulence, direct transmission, and heterologous protection of 4 isolates of H. parasuis (SW114, 12939, MN-H, or 29755) were evaluated using a highly susceptible pig model. In an initial experiment, isolates 12939, MN-H, and 29755 caused Glässer's disease, while strain SW114 failed to cause any clinical signs of disease. One pig from each group challenged with MN-H or 29755 failed to develop clinical disease but were able to transmit the H. parasuis to naïve pigs that subsequently developed Glässer's disease. Pigs colonized with SW114, 29755, or MN-H that were free of clinical disease were protected from rechallenge with isolate 12939. In a following experiment, pigs vaccinated with strain SW114 given as either a bacterin intramuscularly or a live intranasal vaccine were protected from subsequent challenge with isolate 12939; however, some pigs given live SW114 developed arthritis. Overall these studies demonstrate that pigs infected with virulent isolates of H. parasuis can remain healthy and serve as reservoirs for transmission to naïve pigs, and heterologous protection among H. parasuis isolates is possible. In addition, further attenuation of strain SW114 is necessary if it is to be used as a live vaccine.