Plaque Types and Cell-Free Virus From Tissue Cultures Infected With Cal-1 Strain of Herpesvirus Associated With Marek's Disease<xref ref-type="fn" rid="FN2">2</xref>

Abstract

Two plaque types were detected on serial passage of the Cal-1 strain of Marek's disease (MD) agent in chick kidney cell (CKC) cultures. The smaller type 1 plaque, normally observed on primary isolation of the agent from chickens infected with MD, was replaced by a larger type 2 plaque by the fourteenth serial passage. The type 2 plaques grew more rapidly. By the 5th—6th day the plaques were 1.0–2.5 mm in diameter and characterized by pronounced cytoplasmic vacuolation of the affected cells, followed by lysis. Intranuclear inclusions were more frequent in cells of the type 2 plaques than in cells of the type 1 plaques. The addition of 10% dimethylsulfoxide and 10% fetal calf serum to Eagle's basal medium resulted in a marked sparing effect as demonstrated by recovery of infectious virus from CKC cultures after freezing and thawing, sonic disruption, centrifugation, or vibration. Virus, producing type 2 plaques, was recovered from filtrates of supernatants of cell cultures as well as CKC cultures disrupted by freezing and thawing and passed through a 1.2 μ Millipore membrane. The addition of inactivated and concentrated Sendai virus did not materially increase the yield of MD virus in CKC cultures, but fusion of cells appeared to increase recovery of virus that produced type 1 and type 2 plaques.