DETECTION BY ELISA OF BLUETONGUE ANTIGEN DIRECTLY IN THE BLOOD OF EXPERIMENTALLY INFECTED SHEEP

An antigen-capture ELISA (Ag-ELISA) was developed to detect bluetongue virus (BTV) antigen directly from blood samples. Four blood preparati ons [whole blood, buffy coat, washed red blood cells (RBC) and plasma] taken pre-inoculation and on days 6 to 9 post-inoculation (PI) were u sed in the ELISA to study antigenaemia in forty sheep, each experiment ally infected with one of 20 South African BTV serotypes. Seventeen of the 20 serotypes were detected and 27 of the 40 sheep were at some st age Ag-ELISA positive, Over the period of sampling, Ag-ELISA positive results were most frequently returned from whole blood taken on days 6 and 7 PI. However in some instances the quantity and/or duration of B TV antigenaemia was greater in buffy coat and washed RBC preparations. In a selection of samples examined, positive Ag-ELISA results were ge nerally obtained when samples had an infectious virus titre in eggs of > 10(3.2) egg lethal doses (ELD(50)/ml). The appearance and duration of detectable antigenaemia was compared with the development of clinic al signs and antibody responses of infected sheep. On days 6 and 7 PI the presence of fever (> 40 degrees C) was indicative to the likelihoo d of detectable antigenaemia After day 7 PI antigenaemia declined and clinical signs of swollen face and inflamed feet appeared together wit h the first detectable antibody response. The Ag-ELISA, when used in c onjunction with clinical observations and serologic data, should be us eful as a rapid diagnostic procedure for bluetongue disease.