Complement-Fixing Antibodies in Sera of Sheep Affected with Visna and Maedi

Complement-fixing antibodies in sera of sheep infected with mædi and visna virus were demonstrated by using as antigen infected tissue culture fluid containing titers of 5 × 105 or more virus particles/ml. Complement-fixing antibodies in these two clinical conditions appear shortly after experimental infection, rise to a high titer and remain at a high level for years. Such antibodies can be found in sera from mædi-infected sheep without detectable neutralizing antibodies.