Distribution of bluetongue virus in tissues of experimentally infected pregnant dogs as determined by in situ hybridization.

Six female dogs (four pregnant and two nonpregnant) were inoculated with bluetongue virus (BTV), serotype 11. Pregnant animals and one nonpregnant dog received 5.5-6.3 log10 of cell culture-adapted virus. The other nonpregnant dog received a modified live vaccine contaminated with bluetongue virus. The non-pregnant animals never became clinically ill and were euthanatized 35 days post-inoculation. Three of the four pregnant dogs aborted, and all four died or were euthanatized 5-10 days post-inoculation. The predominant pathologic feature in the adults was severe pulmonary edema. Various tissues from the bitches and fetuses were examined by in situ hybridization using a digoxigenin-labeled probe corresponding to the nonstructural protein-1 gene of BTV-17. By this technique, viral nucleic acid was detected predominantly in endothelial cells of lung of all four dogs, with lesser amounts in capillaries of uterus, spleen, and kidney in some of the dogs. In two adult dogs, bluetongue viral nucleic acid was detected in mononuclear cells of the periarteriolar lymphoid sheaths of spleen. There was minimal staining of capillaries in placenta in three of the five fetuses examined. There was no viral nucleic acid detected in any of the other fetal tissues.