Control of avian encephalomyelitis: A historical account

Avian encephalomyelitis control methods were not developed until the 1950s although the disease had been discovered and described over 20 yr earlier, inability to transmit che infection by other than intracerebral inoculation , lack of suitable immunologic methods. the unknowing use of immune chicken s or embryos for experimental studies, and reliance on a highly adapted str ain of virus rather than fresh held isolates were the main reasons for a ge neral lack of progress. In the absence of supportive experimental data, at least two commercial breeding organizations turned to the use of a crude th icken brain-propagated virus for vaccination of breeder replacement flocks in the 1950s. This control procedure turned out to be practical and efficac ious. Development of suitable embryo infection methods and immunologic test s and the chance finding that antibody-free flocks were essential for exper imental studies led to the development of embryo-susceptibility tests to id entify immune breeder Becks and formed the basis for another commercially a pplied control program, the testing and selection of only immune hocks for hatching purposes. The application of the new testing methods coupled with a switch from the adapted Van Roekel strain of virus to fresh field isolate s for experimentation resulted in a rapid unraveling of the epizootiology a nd pathogenesis of the disease and also to the development of a safe and ef fective vaccine that was licensed for administration to breeder replacement s in 1962.