African swine fever. IV. Demonstration of the viral antigen by means of immunofluorescence.

African swine fever immunofluorescent conjugates were prepared in swine and used successfully in the demonstration of viral antigen in frozen tissue sections and in inoculated tissue culture cells. Cross reactivity was observed with the six strains used in the inoculation of swine. The high antibody content of the serum of immune swine did not interfere with demonstration of the antigen in frozen tissue sections of certain of their organs. The localisation and extent of antigen varied with the stage of infection. The virus was demonstrated in spleen and other organs as early as after one day of pyrexia and until after death of the animal. A pool of hog cholera and African swine fever conjugates stained with dyes of different colours was used in the localisation of respective antigens in experimental mixed infection.