Early polykaryocytosis inhibition test: evaluation of its performance in a seroepidemiological survey of bovine leukemia virus induced antibodies in cattle.

We report the results of a seroepidemiological survey, using the recently described early polykaryocytosis inhibition (EPI) assay to detect bovine leukemia virus (BLV) infection in cattle. At the herd level, there is a good correlation between epidemiological, hematological, anatomopathological data and of both the presence and titer of EP inhibiting antibodies. The EPI procedure revealed to be more sensitive than two other routine serological techniques, complement fixation and immunodiffusion. In addition, at the individual level the average EPI titers of the sera increase progressively from normal to hematologically-suspect, -- positive and finally to lymphosarcomatous animals; when the age is considered, there is a very significant increase of the amount of EP inhibiting antibodies among lymphocytotic animals, while there is only a very moderate increase of the EPI titer among hematologically normal contact animals. This suggests a loss of control of BLV expression in most lymphocytotic animals and may explain the more frequent occurrence of lymphosarcomas in this category of animals. The horizontal transmission of BLV throughout the entire life span is supported by the observation of an increase with age of the percentage of animals with EP inhibiting antibodies.