Infectious units

There is much concern for the safety of personnel handling articles contaminated with pathogenic viruses such as hepatitis B virus (HB V) and human immunodeficiency vims (HIV) which causes acquired immune deficiency syndrome (AIDS). Some agents have been recommended for disinfection of HBV and HIV depending on the circumstances and level of contamination these are hsted in Table 10.4. Disinfectants must be able to treat rapidly and reliably accidental spills of blood, body fluids or secretions from HIV infected patients. Such spills may contain levels of HIV as high as lO" infectious units/ml. Recent evidence Irom the Medical Devices Agency evaluation of disinfectants against HIV indicated that few chemicals could destroy the vims in a... 

In order to obtain any significant understanding of the nature of viruses and virus replication, it is necessary to be able to quantify the number of virus particles. Virus particles are almost always too small to be seen under the light microscope. Although virus particles can be observed under the electron microscope, the use of this instrument is cumbersome for routine study. In general, viruses are quantified by measuring their effects on the host cells which they infect. It is common to speak of a virus infectious unit, which is the. smallest unit that causes a detectable effect when placed with a susceptible host. By determining the number of infectious units per... 

Figure 9.1 The viral infectious unit, or virion, consists of a nucleic acid encased in a protein shell. The various structural components of the virion exhibit differing functional properties and thus afford a variety of targets for antiviral drug design.

Purity silver staining/coomassie blue " Potency infectious unit titer " Strength vector genome titer " Strength capsid particle titer" rcAAV ... 

Set up a series of tubes containing 0.9 ml BSS or PBS or Eagle s medium without serum and to the first tube add 0.1 ml virus stock. Mix the contents and remove 0.1 ml to the second tube and so on. A solution is required which contains 200-400 infectious units per ml and usually the 10 5 to 10 9 dilutions are assayed. 

The first round of biopanning is critical to achieve success. Ordinarily, each clone is represented by only 100 infectious units (I.U.) in the original library. 

To find whether the reduced foci formation was due to inhibition of MSV (M) replication, the effect of these compounds on virus growth was studied. Secondary mouse embryo cell cultures were infected with MSV (M) at the rate of 0.03 competent MSV infectious units per cell and treated with the compounds at different doses after the infection by the focus assay in the presence of an optimal amount of MLV (M) (1.01 10s Leukemia Vims Helper Units) according to Hirschman etal.33 Similarly treated uninfected cultures were trypsinized at the same time, and cells were counted. 

Numbers of cell culture infectious doses or animal infectious units. 

Transmission of Salmonella typhi may also occur in day care centers and schools by direct contact with the fecal-oral route. Particularly attention should be taken by nursing and medical personnel in infectious units who care for patients with Salmonellosis and typhoid fever. 

Determining the Infectious Units of the Stock Phage Library Solution... 

Determine the infectious units of the dialyzed phage library as described in Subheading 3.2. 

Although PrP-res is associated with TSE infectivity and has, at the biochemical level at least, some limited self-propagating activity, important questions remain about the PrP-only prion model for the TSE agent. For instance, why has no one been able to demonstrate the model s most basic prediction, that is, that PrP-sen alone can be induced to convert to an infectious agent that causes TSE disease when inoculated into animals Inoculation of a synthetic PrP peptide has induced a TSE-like disease in transgenic mice expressing a familial TSE associated mutant PrP, but the serial transmissibility of this disease remains to be determined (Kaneko et al, 2000). Why are 100,000 PrP-res molecules present per infectious unit Why is PrP-res not always found in infectious tissues (Lasmezas et al, 1997) Why are nucleic acids (Akowitz et al,... 

Viruses are either measured as infectious units, i.e., in terms of their ability to infect, multiply and produce progeny or as viral particles, regardless of their function as infectious agents [7]. 

Titration means the measurement of the amount of virus in terms of the number of infectious unites per unit volume. 

Some viruses destroy cells they infect but do not produce the necessary CPE for visible plaque formation. These viruses are titrated by serial dilution end point method. Serial dilutions of virus suspensions are inoculated into cell monolayers which are then incubated until the cell sheets show clear signs of cell s destruction. The end point is the dilution that gives a positive (cell-destroying) reaction and originally contains at least one infectious unit. 

Perhaps as a consequence of their adaptation to dissimilar hosts in nature, the alphaviruses replicate readily, and generally to very high titers, in a wide range of cell types and culture conditions in vitro. Virus titers of 1 billion infectious units per milliliter are not unusual, and the viruses are stable in storage and in a variety of laboratory procedures. Because of the relative ease with which these viruses can be manipulated in the laboratory, they have long served as model systems by which to study various aspects of virus replication, pathogenesis, induction of immune responses, and virus-vector relationships. As a result, the alphaviruses are well described and their characteristics well defined.1213... 

To calculate the virus titer (measured as infectious units (lU) per mL) insert the virus dilution factors (250, 500, 1000, or 2000), number of cells in the well at the time of transfection, percent infected cells from the GP64 assay (%GP64) and the volume of inoculum (0.02 mL) into the equations below. For samples with <30% of the cells infected use ... 

The absorbency index per particle Op (260 m/z) contains a correction for light scattering and has the units of cm. per particle. Values of 4.5 X 10 to 7.5 X lO cm. per particle have been reported by Luria et at. (204) for T2 and T6 preparations in which the ratio of infectious units to the absolute number of particles varied from 0.4 to 0.7. The figure of 2.7 X 10 cm. per particle has been given for the smaller phage T7 (262). Herriott and Barlow (130) found that the titer varied only from 1.1 to 1.3 X 10 for 5 preparations of T2 phage. This, without correction for scattering, corresponds to an absorbency index of about 8.5 X 10 cm. per particle. 

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