Quantitative studies on meningopneumonitis virus.

Abstract

Using dialyzed allantoic fluid suspensions of meningopneumonitis virus, Crocker (1954) studied the ratio of numbers of virus particles, as determined by electron microscopy, to egg infectivity. He reported the number of particles per egg LDso to vary from 200 to 1000. Zahler and Moulder (1953) used the method of Gogolak (1953), in which stained virus particles are counted by light microscopy, to study feline pneumonitis virus from yolk sac. They reported the number of particles per egg LD50 to be about 100. More recently, Moulder et al. (1956) reported a ratio of about 20 particles per egg LD50 of partially purified yolk sac-grown feline pneumonitis virus. Weiss and Huang (1954) obtained data from infected tissue cultures indicating that a single particle is probably sufficient to infect a susceptible cell, with all virus preparations having apparently a high proportion of inactive particles. Total nitrogen determinations have been used frequently to follow purification of feline and murine pneumonitis virus in yolk sac suspensions and various results have been reported. Brown et al. (1952) reported 10-11 65 to 10-12 08 g of nitrogen per LD50 of the feline virus; Gogolak (1953) found 10s1305 g nitrogen per particle of the murine virus; Zahler and Moulder (1953) found 10-11.5 to 10-12 g nitrogen per LD50 or about 10-'4 g per particle for feline virus. In a preliminary report, Smith and Manire (1959) used a modification of Gogolak's technique and presented evidence of its precision and accuracy in counting particles of purified allantoic fluid-grown meningopneumonitis virus. One egg LD50 was found to contain an average of 145 particles and 1 ,ug nitrogen was found in 108 particles (1 particle = 10-14 g nitrogen). The experiments reported here were initiated as a part of a study on the toxicity of meningo-