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Diagnosis of bovine leukemia virus infection: evaluation of serologic and hematologic tests by a direct infectivity detection assay.

J. F. Ferrer,C. E. Piper,Abt Da,R. Marshak

Published 1977 in American Journal of Veterinary Research

ABSTRACT

This study shows that the syncytia infectivity assay (sia) is more sensitive than electron microscopy for the direct diagnosis of bovine leukemia virus (blv) infection. The sia was also applied in a critical assessment of the value of the virus-neutralization, immunofluorescent, and agar gel diffusion tests for the diagnosis of blv infection in cattle ranging in age from birth to adulthood. The virus-neutralization test is based on the specific inhibition of blv-induced syncytia by serum antibodies directed against the virion envelope antigens. The immunofluorescent test uses acetone-fixed blv-infected lymphocytes as targets and detects antibodies to the major internal virion antigen. The agar gel immunodiffusion test (using ether-treated blv) detects antibodies to the same viral antigen. Of 141 serum samples obtained from actively infected cattle, 140 (99%) were positive in the virus-neutralization antibody test. Conversely, antibodies were not detected in any of the 137 samples collected from uninfected cattle before nursing and after 7 months of age. The virus-neutralization antibody test may therefore be used to identify both blv infected and uninfected cattle. Eighty-nine percent of the serum samples from infected cattle were positive in the immunofluorescent test. In contrast, the agar gel immunodiffusion test failed to detect viral antibodies in 64% of the serum samples from infected cattle that were positive in the virus-neutralization test. Only 28.5% of the adult cattle infected with blv were positive in a hematologic key for persistent lymphocytosis. After the ingestion of colostrum, and until the age of 3 to 5 months, maternal antibodies against blv were detected in both blv-infected and noninfected calves born to infected dams. Thus, the diagnosis of blv infection in this age span requires direct demonstration of the virus by the sia. As shown by the present results, neither passively acquired nor actively produced antibodies are effective in arresting an established blv infection in cattle. The present work extends previous results from this laboratory showing that prenatal vertical transmission of blv occasionally occurs.

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