▁ ▁High ▁pre val ence ▁of ▁virus ▁was ▁found ▁from ▁testing ▁by ▁US DA . ▁" As ▁part ▁of ▁the ▁ 2 0 0 7 ▁da iry ▁study , ▁bulk ▁tank ▁milk ▁was ▁collected ▁from ▁ 5 3 4 ▁operations ▁with ▁ 3 0 ▁or ▁more ▁da iry ▁c ows ▁and ▁tested ▁with ▁an ▁En zym e ▁Linked - Im m unos orb ent ▁Ass ay ▁( EL IS A ) ▁for ▁the ▁presence ▁of ▁ant ib od ies ▁against ▁B L V . ▁Results ▁showed ▁that ▁ 8 3 . 9 ▁percent ▁of ▁U . S . ▁da iry ▁operations ▁were ▁positive ▁for ▁B L V ▁( table ▁ 1 ). " ▁B L V ▁in fection ▁can ▁be ▁detected ▁by ▁EL IS A ▁or ▁PC R . ▁ ▁Pot ential ▁in fection ▁in ▁humans ▁ ▁So on ▁after ▁B L V ▁was ▁discovered ▁in ▁the ▁ 1 9 7 0 s , ▁ten ▁studies ▁were ▁done ▁looking ▁for ▁ant ib od ies ▁to ▁B L V ▁in ▁humans . ▁However , ▁no ▁ant ib od ies ▁were ▁found ▁and ▁so ▁research ers ▁concluded ▁that ▁B L V ▁was ▁not ▁a ▁risk ▁to ▁human ▁health . ▁However , ▁the ▁development ▁of ▁more ▁sensitive ▁techniques ▁for ▁detect ing ▁ant ib od ies ▁developed , ▁and ▁in ▁ 2 0 0 3 ▁a ▁test ▁of ▁more ▁than ▁ 2 0 0 ▁people ▁using ▁these ▁new ▁tests ▁found ▁that ▁more ▁than ▁a ▁third ▁carried ▁ant ib od ies ▁re active ▁to ▁B L V ,