Clinical course and pathogenicity of variant rabbit haemorrhagic disease virus in experimentally infected adult and kit rabbits: Significance towards control and spread

•Rapid death of kits due to RHDV-N11 fever and viraemia the only clinical signs.•Lesions were more frequent and severe in RHDV-N11 infected young rabbit tissues.•Intestinal lesions due to RHDV-N11 were only detected in kits.•Surviving rabbits shed virus via respiratory-faecal routes at least up to 7 DPI.•The faecal route was the main source of disseminating virus. RHDVb has become the dominant RHDV on the Iberian Peninsula. A better understanding of its pathogenicity is required to aid control measures. Thus, the clinical course, humoral immune response, viraemia and kinetics of RHDV-N11 (a Spanish RHDVb isolate) infection in different tissues at both viral RNA and protein levels were studied in experimentally infected young and adult rabbits. The case fatality rate differed between the two age groups, with 21% of kits succumbing while no deaths were observed in adults. Fever and viremia were strongly associated with death, which occurred 48 h post infection (PI) too fast for an effective humoral immune response to be mounted. A significant effect on the number of viral RNA copies with regard to the variables age, tissue and time PI (p