Bluetongue virus does not persist in naturally infected cattle

Studies were designed to test if observations by Takamatsu et al. in 2003 were applicable to natural infection of cattle with bluetongue virus (BTV). These observations suggested that ovine gamma delta T-cells could become persistently infected and subsequent midge feeding could induce virus replication. Skin biopsies and blood were collected from 28 cattle naturally infected with BTV-1. Blood samples were processed for virus isolation by embryonated chicken egg inoculation and for serology by BTV competitive enzyme-linked immunosorbent assay and BTV-1 virus neutralisation. BTV-1 was isolated from the blood of all animals and serology confirmed infection with BTV-1. A total of 288 skin biopsies were collected and cultured in the presence of interleukin 2 and epidermal growth factor. Sampling commenced as soon as either serology or virus isolation indicated infection with BTV and continued at weekly intervals for at least eight weeks then monthly for another two months. The natural viraemias in this experiment ranged from one to five weeks. BTV-1 was isolated from only one skin biopsy sample. This sample was collected during the week in which the animal was viraemic. These findings provide compelling evidence that BTV does not persist in gamma delta T-cells in the skin of naturally infected cattle.