Antibodies to bovine leukemia virus and presence of malignant lymphoma in slaughtered California dairy cattle.

Rates of malignant lymphoma (ML) in California dairy cattle and relationships between ML and presence of antibodies to bovine leukemia virus (BLV) were investigated. An excessively high rate of lymphoma was found in the population studied and a previously unknown relationship between ML and p-24 antibodies to BLV was identified. Sera from slaughtered California holstein dairy cows were tested by agar gel immunodiffusion for presence of antibodies to the gp-51 and p-24 antigens of BLV. Of the 7,760 cows slaughtered, 32% and 10% had gp-51 and p-24 antibodies, respectively, and 52 cows (0.67%) were condemned for ML. Lymphoma was diagnosed histopathologically in 37 (86%) of 43 cows sampled from those 52 condemned. Highly elevated prevalence rates of ML in gp-51 and p-24 antibody-positive cows were 172.6 and 511.5 per 10,000 cows, respectively. A prevalence rate of lymphoma not associated with presence of BLV antibodies was estimated for the first time to be 1.55 per 10,000 cows. A highly significant (P less than .00001) and strong (odds ratio = 26.0) association was found between presence of p-24 antibodies and presence of ML for cows with gp-51 antibodies. When results of serologic tests were compared in regard to diagnosis of ML, the highest sensitivity was with use of gp-51 serology alone (97.3%) and highest specificity was with use of p-24 serology alone (90.4%). False-negative and false-positive rates of diagnosis of ML for gp-51-positive, p-24-negative and gp-51-positive, p-24-positive cows were 0.21 and 94.8%, respectively.