After an initial replication in agranular leucocytes at the site of inoculation and in regional lymph nodes, infected lymphocytes, monocytes, dendritic cells, and macrophages disseminate the virus to secondary sites (mainly lungs, spleen, and lymph nodes). Infectious BTV can be detected associated with erythrocytes, in which it does not replicate but persists in invaginations of cell membranes. Association of infectious BTV with erythrocytes is detected soon after infection (24 h) and persists throughout the duration of viraemia, protecting the virus from immune clearance. In ruminants a prolonged cell-associated viraemia persists even in the presence of high levels of neutralizing antibodies. Infectious virus had been isolated from blood samples collected until 60 days postinfection in cattles. According to species, age, and serotype, BTV RNA can be detected by RT-PCR long after.
