Bluetongue virus serotype 20 infection in pregnant Merino sheep

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Abstract
Eleven maiden Merino ewes, free of antibody to bluetongue virus serotype 20 (BTV-20) in agar gel immunodiffusion and serum neutralization tests, were mated once with a ram. Ten ewes were inoculated with BTV-20 35-42 days after service, and 1 ewe was left as an uninoculated control. One of the inoculated ewes and the control ewe remained uninfected throughout the experiment. Of the remaining 9 ewes, 8 showed clinical signs ranging from mild to moderate, and the other showed no clinical signs of infection. BTV-20 viremia was detected in ewes between days 3 and 11 post inoculation, and the serum antibody response was followed. The control ewe and 5 of 9 infected ewes were pregnant when examined 90-97 days after service. Each of these animals produced a normal lamb. There was no evidence of abortion in the remaining 5 ewes, and no transplacental transfer of virus was detected in the lambs of the 5 infected ewes. At necropsy, 46 days after the birth of the last lamb, no gross or microscopic lesions were observed in either the ewes or lambs.