Experiments with inactivated visna-maedi vaccine.

Sixteen Icelandic sheep were vaccinated against Visna-Maedi infection with formalin inactivated whole virus vaccine to which alun was added as an adjuvant. Western Blots showed that all the vaccinees responded to the major proteins of the virus. They all developed neutralizing antibodies ranging in titers from 1/8-1/256 at maximum for individual sheep. Passive transfer of antibodies and neutralizing activity from vaccinated ewes to their lambs was demonstrated. Exposure of the 16 vaccinees and their 16 unvaccinated control sheep to natural infection is attempted by housing them with heavily infected sheep. After 9 months of exposure there is no seroconversion in the unvaccinated group. Only time can tell, whether or not such conventional vaccination with inactivated vaccine protects the vaccinees.