Plaque Formation by an Orphan Virus of Fowls

Abstract

WHEN Sharpless et al. ¹and Fontes et al. ² reported the adaptation of fowl lymphomatosis virus (RPL.12) to chicken embryo tissue culture, and later when plaque assay methods were described for this virus^3–5, there was promise of an in vitro system for the study of viral oncogenesis. However, the suspicion that this virus may not in fact be the causal agent of fowl lymphomatosis was aroused when it was found that the inoculation of high-titre tissue culture material into chickens of a stock known to be susceptible to the ES4 strain of fowl lymphomatosis virus was not followed by the formation of tumours even after six months. Moreover, when these birds were challenged with ES4 virus, they were found to be completely susceptible (Carr, J. G., Macpherson, I. A., and Stoker, M. G. P., unpublished results). It was also shown that a high dilution of pooled normal sera from the ES4 susceptible flock neutralized plaque formation by the virus in tissue culture. A possible explanation of these results is that the virus we were studying was a fowl orphan virus present in poultry stocks. Since then confirmation has been received in personal communications from B. R. Burmester, G. R. Sharpless and R. J. Huebner, respectively, giving results of extensive investigations in the United States. These show that the virus is enzootic in many flocks.