Late immune responses in experimental maedi

Thirteen sheep were inoculated with maedi-visna virus by respiratory or intra-cerebral (i.c.) routes and were kept in close contact with 7 uninoculated control sheep. Immune responses and virological events were followed in all 20 sheep for periods up to 3 years post-inoculation. Three out of 7 i.c. infected sheep produced no complement fixing (CF) or serum neutralising (SN) antibody, whilst all 5 infected by the respiratory route and the hyperimmunised sheep developed CF and SN antibody which persisted with fluctuating titre over the period of study. Ten out of 11 sheep, which were followed from 3 months after experimental inoculation to 16-21 months (5 sheep) or 3 years (6 sheep) after inoculation, developed transient late virus-specific cell-mediated responses with intermittent virus isolation from peripheral blood leucocytes (PBL) over the period of study. In the contact control sheep, virus was isolated from PBL of 2 sheep during the 2nd year of contact, and transient virus-specific cell-mediated responses, but no antibody responses, were detected.