Unusual filterable oncogenic agent isolated from horizontally transmitted Syrian hamster lymphomas

An outbreak of horizontally transmitted malignant lymphoma in an experimental hamster holding facility was previously reported. Retroviridae (oncornavirus) or other conventional oncogenic viruses (oncodnaviruses) could not be detected in these lymphomas by immunological methods, direct isolation procedures or electron microscopy but an infectious agents was clearly involved. The incidence of lymphomas during five recurrent epidemics ranged from 50 to 90% in young, inbred and random-bred Syrian golden hamster exposed. The agent seemed to be resistant to UV inactivation, formaldehyde vapour and other viricidal agents (chlorine and iodine), and stable for long periods in the absence of hamster hosts in the contaminated facility. Associated disease syndromes in exposed hamster included severe enteritis, pyelonephritis, the occasional appearance of warts, poor breeding efficiency and intussusception. We now report the successful, cell-free isolation of an unusual, filterable agent prepared in protamine sulphate buffer from primary and animal-passaged lymphomas, which produces lymphomas with good efficiency when injected subcutaneously (s.c.) into newborn Syrian inbred (LSH) and random-bred (LVG) hamster. The agent could be reisolated from these induced lymphomas and injected into other hamsters to reproduce the neoplastic condition. It showed characteristics suggested for a mammalian viroid (a non-encapsidated, DNase-sensitive low-molecular-weight, disease-causing, self-replicating, naturally infectious nucleic acid).