Serological methods to detect calves infected in utero with bovine leukemia virus.

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Abstract
Calves born to dams infected with bovine leukemia virus (BLV) were investigated serologically and virologically before and/or after ingestion of colostrum to develop effective methods to detect BLV-infected calves during early postnatal life. Of 50 precolostral sera, 10 (20%) and 13 (26%) were BLV-antibody positive by immunodiffusion (ID) and virus-neutralization (VN) tests, respectively, indicating in utero BLV infection of the donor calves. In 18 postcolostral sera, ID antibody titers against BLV correlated well with serum ID antibody titers of the respective dams. The colostral antibodies decayed with a half-life of .apprx. 20 days in 76 BLV-uninfected calves. The antibody became undetectable in almost all of the calves at 6 mo. of age. In 16 calves infected in utero with BLV, ID antibody was often detected even at .gtoreq. 6 mo. of age. The pattern of change in individual sequential ID antibody titers of these BLV-infected calves could be divided into 3 types. In type 1, ID antibody titers were maintained from birth to .gtoreq. 7 mo. of age. In types 2 and 3, the antibody titers decreased at a rate similar to those in uninfected calves. The titers then increased again at 5-7 mo. of age in type 2 but they did not appear again after their disappearance in type 3. Calves with antibody changes of types 1, 2 and 3 were 6 (37.5%), 6 (37.5%) and 4 (25.0%), respectively. By testing sequential antibody titers, it was revealed that 7 (11.7%) of 60 calves which could not be tested for precolostral antibodies showed antibody changes of types 1 and 2, indicating BLV infection in utero. Methods to detect BLV-infected calves during early postnatal life are discussed.