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Experimental infection of calves by two genetically-distinct strains of rift valley fever virus

William C. Wilson, A. Sally Davis, Natasha N. Gaudreault, Bonto Faburay, Jessie D. Trujillo, Vinay Shivanna, Sun Young Sunwoo, Aaron Balogh, Abaineh Endalew, Wenjun Ma, Barbara S. Drolet, Mark G. Ruder, Igor Morozov, D. Scott McVey, Juergen A. Richt
Viruses 2016 v.8 no.5 pp. 1-16
neutralization, liver, sheep, vaccines, beef cattle, Rift Valley fever, viremia, Rift Valley fever phlebovirus, pathogenesis, viruses, animal models, neutralizing antibodies, viral load, neonates, temperature, calves, virulence, mortality, mixed breeds
Recent outbreaks of Rift Valley fever in ruminant livestock, characterized by mass abortion and high mortality rates in neonates, have raised international interest in improving vaccine control strategies. Previously we developed a reliable challenge model for sheep that improves the evaluation of existing and novel vaccines in sheep. This sheep model demonstrated differences in the pathogenesis of Rift Valley fever virus (RVFV) infection between two genetically distinct wild type strains of the virus, Saudi Arabia 2001 (SA01) and Kenya 2006 (Ken06). Here we evaluated the pathogenicity of these two RVFV strains in mixed breed beef calves. There was a transient increase in rectal temperatures with both virus strains, but this clinical sign was less consistent than previously reported with sheep. Three of the five Ken06 infected animals had an early-onset viremia, 1 day post infection (dpi), with viremia lasting at least three days. The same number of SA01 infected animals developed viremia at 2 dpi, but it only persisted through 3 dpi in one animal. The average virus titer for the SA01 infected calves was 1.6 logs less than for the Ken06 infected calves. Calves, inoculated with either strain, seroconverted by 5 dpi and showed time-dependent increases in their virus neutralizing antibody titers. Consistent with results obtained in the previous sheep study, elevated liver enzyme levels, more severe liver pathology, and higher virus titers occurred with the Ken06 strain as compared to the SA01 strain. These results demonstrate the establishment of a virulent challenge model for vaccine evaluation in calves.