A method for the control of lymphoid leukosis in chickens.

Lymphoid leukosis (LL) was eliminated from 3 inbred lines of White Leghorn chickens that were temporarily kept in isolation. The method of control was based on three elements: 1) From an infected flock we selected hens that produced LL virus-free eggs. Pooled extracts from groups of embryos were tested for vertical virus transmission by the nonproducer cell activation test. 2) Only eggs from dams that did not congenitally shed virus to their embryos were used to produce progeny. The offspring were reared in isolation for 2 months (at which time the age-related resistance against tumor formation had developed sufficiently). 3) The birds were subsequently inoculated im with 10(5) mean tissue culture infective doses of LL viruses of subgroups A and B and transferred to a conventional chicken house. The controlled exposure provided immunity against LL virus infection in a highly infect environment. This procedure resulted in birds a) with no boservable LL, and b) producing LL virus-free eggs. To obtain flocks that had no LL and produced virus-free progeny, the procedure had to be repeated for at least two generations due to the intermittent virus excretion that often occurred.