Equivalence between Vaccinia Particles Counted by Electron Microscopy and Infectious Units of the Virus

Overman, John R.; Tamm, Igor

doi:10.3181/00379727-92-22621

Cited by 21 publications

(11 citation statements)

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“…The ratios of almost unity of total to infective vaccinia virus particles ( T / I ) found by Overman & Tamm (1956) are considerably lower than those reported here. However, we suspect that their method of estimating the total count may well have given too low a figure because some virus was not picked up on the supports and some was obscured by debris.…”

Section: Discussioncontrasting

confidence: 47%

The Infectivity of Purified and Partially Purified Preparations of Vaccinia and Cowpox Viruses

Kaplan

Valentine

1959

Journal of General Microbiology

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SUMMARY: Twenty-three preparations of vaccinia virus and 5 of cowpox virus were examined by electron microscopy of spray droplets and by infectivity titrations at various stages of purification. Extraction of virus-containing tissues with a fluorocarbon compound was a useful early step in purification, but preparations of the highest purity were obtained by flocculation of the virus with M-NaCl. The average ratio of total particle count to infectivity for the vaccinia virus preparations was 12. The lowest observed ratio based on reliable particle counts was 3.4.During inactivation of vaccinia virus, a very small, but constant, fraction of infectivity was observed t o survive extremely high doses of gamma-radiation .In order to assess the likelihood of multiple reactivation being responsible for this persistence, it was necessary to know the ratio of infective units to total particle count in the type of virus preparation being irradiated. The two groups of published figures for vaccinia virus are not in close agreement, so several preparations of vaccinia virus, and a few of cowpox virus, were counted by electron microscopy and titrated for infectivity. The influence of various methods of purification on the preparations was also studied. METHODS Viruses.The vaccinia virus strains were all sublines of the Lister Institute vaccine strain. The rabbit dermal virus (RV) was a homogeneous line (Amies, 1938) in its 80th skin passage. Chick embryo adapted virus (LC) had been passed from 13 to 16 times in the chick embryo chorioallantois. Tissue culture virus (T) was taken from the first five batches of virus grown for smallpox vaccine preparation. This virus was a first passage of bacteriologically sterile RV in trypsinized chick embryo cells. The cozupoe virus was a strain lyophilized in 1939 and recently cultivated. Its history is unknown, but it produced typical haemorrhagic lesions in the chick embryo chorioallantois after 3 days of incubation.Diluent. All extractions and dilutions were made in McIlvaine's phosphate + citrate buffer (pH 7.2, 0.004 M-phosphate). Treatments with trypsin were done with Armour's crystalline, salt-free product.Extractions were made by mechanical disruption of the virus-infected tissues in a Servall 'Omnimix' homogenizer a t 14,000 rev./min. for 5 min., with an ice-bath round the stainless steel vessel. Trifluorotrichloroethane (Gessler,

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Section: Discussioncontrasting

confidence: 47%

The Infectivity of Purified and Partially Purified Preparations of Vaccinia and Cowpox Viruses

Kaplan

Valentine

1959

Journal of General Microbiology

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“…Furthermore, discrepancy between the data of Overman and Tamm (1956) and those of Dumbel et al (1957) concerning the particle number representing one pock-forming unit of vaccinia virus would seem to render this direct method unapplicable for such a study as our present one where a very subtle difference should be pursued. Therefore, within the technical limit now allowed for us to reach, our investigations will give no other conclusions than that the baby mouse MIU may be an equivalent among many strains of rabies virus and quantitation of all rabies virus strains should be adjusted to the basis of baby mouse MIU as a common measuring unit especially when comparison is made among different strains or different lines.…”

Section: Discussionmentioning

confidence: 71%

Inffction of the One-Day Old Fertile Hen's Egg With Rabies Virus Iv. A Quantitative Analysis of Infective Units for Mice (Miu) and for One-Day Eggs (Oiu)

Kondo¹

1958

JJMSB

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In our previous work , mouse fixed CVS as well as earlier 7-day egg passage of Flury strain showed nearly equal infective titers in both 1-day egg ID and mouse LD tests, but serial passage in 1-day eggs resulted in an increase approximately ten-foldly in the ratio of 1-day egg 1D to mouse LD titers.At first, it was expected that this difference between the two titers would become increasingly more pronounced as passages were repeated in 1-day eggs until finally the mouse infectivity would be lost. However, quite contrary to this expectation, the 1-day egg passage strains, COP and FOP, even after many passages through 1-day eggs did not alter this ratio and sustained as much infectivity for adult mice as did respective mother strains, CVS and Flury.Then became important the question of whether or not one mouse LD (MIU) of the 1-day egg-adapted lines was equivalent to that of their mother viruses in terms of viral particle number.If one mouse LD of a mother strain represented N particles while that of its 1-day egg-adapted line corresponded to pN particles, a direct comparison of viral yields between these two viruses might be possible only after correction of the latter titer by the factor of p.As was previously demonstrated (Yoshino et at., 1956 a), the peak viral concentration in the embryo obtained by the infection of 1-day eggs was as high as was reached in the mouse brain when both titers were expressed in terms of MIUs and therefore it was thought possible that more detailed investigations on the quantitative significance of MIU would revise our previous view concerning the viral yield in such young embryos.Approaches to this problem were quite difficult, because we had to resort only to indirect measurements of virus particles such as animal infectivity tests.However, the use of baby mice, which were found to be more susceptible than adult mice, and neutralization tests with a rabbit antiserum seemed to cast light on the solution of this problem.In order to avoid complexity, studies were confined to the relation between the mousefixed CVS and its 1-day egg passage line COP as a representative combination.The results obtained appeared to point to an equal equivalence of MIU between these two viruses. It was also noticed that, in the ordinary titration employing

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“…Across different experimental systems the number of poxvirus per infectious unit has been found to vary, but it appears that favorable conditions enable all virus particles to infect (Overman & Tamm, 1956;Parker, Bronson, & Green, 1941;Sprunt & McDearman, 1940). Further, we see no biologically plausible reason that the one-hit model would not apply to inhaled virus.…”

Section: Discussionmentioning

confidence: 95%

The Infectious Dose of Variola (Smallpox) Virus

et al. 2004

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Quantitative estimation of an individual's risk of infection due to airborne pathogens requires knowledge of the pathogen's infectious dose, in addition to estimates of the pathogen's airborne concentration and the person's exposure duration. Based on our review of the published literature on poxvirus infection, we conclude that the infectious dose of variola (smallpox) virus is likely one virus particle and that infection can be initiated in either the upper respiratory tract or pulmonary region. Studies of airborne transmission of poxvirus in monkeys and rabbits show that primary infection can occur in both regions of the respiratory tract. A quantitative study of poxvirus inhalation transmission in rabbits indicates that the deposition of one pock-forming unit (PFU) carried on respirable particles can cause infection. Findings in both in vitro and in vivo studies of the number of virus particles comprising a PFU are consistent with a "one-hit" phenomenon-namely, the cellular uptake of just one virus particle can lead to infection of a cell or an area of cell growth, creating a pock (an infected area of cells). Variability in virulence among different virus strains may involve differences inthe probability of infection per virus particle, where a highly virulent strain has a probability close to one of successful infection for each virus particle. In an analogous manner, variability in susceptibility to the same virus strain among different hosts may involve differences in the probability of infection per virus particle across different hosts. Applied Biosafety, 9(3) pp. 118-127

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Equivalence between Vaccinia Particles Counted by Electron Microscopy and Infectious Units of the Virus

Cited by 21 publications

References 0 publications

The Infectivity of Purified and Partially Purified Preparations of Vaccinia and Cowpox Viruses

The Infectivity of Purified and Partially Purified Preparations of Vaccinia and Cowpox Viruses

Inffction of the One-Day Old Fertile Hen's Egg With Rabies Virus Iv. A Quantitative Analysis of Infective Units for Mice (Miu) and for One-Day Eggs (Oiu)

The Infectious Dose of Variola (Smallpox) Virus

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