Location: Virus and Prion ResearchTitle: Virulence, transmission, and heterologous protection of four isolates of Haemophilus parasuis Author
|Kehrli Jr, Marcus|
Submitted to: Clinical and Vaccine Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2013
Publication Date: 9/1/2013
Publication URL: http://handle.nal.usda.gov/10113/61365
Citation: Brockmeier, S.L., Loving, C.L., Mullins, M., Register, K.B., Nicholson, T.L., Wiseman, B.S., Baker, R.B., Kehrli, Jr., M.E. 2013. Virulence, transmission, and heterologous protection of four isolates of Haemophilus parasuis. Clinical and Vaccine Immunology. 20(9):1466-1472. Interpretive Summary: Haemophilus parasuis is a bacterium that causes Glässer's disease in swine, a disease characterized by chronic debilitation and often death that costs the swine industry millions in losses annually. However, not all strains of the bacterium cause disease. To date, little is known about genetic differences among H. parasuis strains and genetic factors that contribute to its ability to cause disease. Also, current vaccines made against one strain often don't protect against other strains. The goal of this study was to directly compare four isolates of the bacterium for their ability to cause disease in pigs. Three of the isolates caused disease in the pigs, while pigs given the fourth isolate remained healthy. Pigs that were vaccinated with the isolate that did not cause disease were subsequently protected from disease when exposed to one of the disease causing isolates. Thus, strains of H. parasuis that don't cause disease can be used as a vaccine to protect pigs against disease causing strains, and DNA sequencing can now be used to compare the genomes of the different isolates for identification of genes contributing to the ability of H. parasuis to cause disease. These results can be used by swine producers to control losses from this disease and identify whether strains of H. parasuis circulating on the farm are capable of causing disease.
Technical Abstract: 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.