Some characteristics of cell-free preparations of Marek's disease virus

Crude cell-free preparations of JM strain Marek's disease virus, obtained from the skin of infected chickens, were studied. Infectious virus survived several freeze-thaw cycles and at least 10 minutes of sonic vibration without appreciable loss of titer. It passed through a Millipore filter membrane with average pore diameter of 300 but not 220 mμ. All infectious virus was sedimented by centrifugation at 5,000 × g for 1 hour. Some virus survived 10-minute treatments at pH 4.0 or 10.0 but not at 3.0 or 11.0. Virus did not lose titer in several months at -65 C, but infectivity was markedly reduced in samples stored at -20 C for 4 months. Inactivation was complete within 2 weeks at 4 C, 4 days at 22-25 C, 18 hours at 37 C, 30 minutes at 56 C, and 10 minutes at 60 C. Virus was neutralized by specific antibody, and parallel virus titrations in chicks and cell cultures indicated about equal sensitivity for assays in the two host systems.