Читать книгу Principles of Virology - Jane Flint, S. Jane Flint - Страница 87

The end-point dilution assay provided a means to determine virus titer before the development of the plaque assay. It is still used for measuring the titers of certain viruses that do not form plaques or for determining the virulence of a virus in animals. Serial dilutions of a virus stock are inoculated into replicate test units (typically 8 to 10), which can be cell cultures, eggs, or animals. The number of test units that have become infected is then determined for each virus dilution. In cell culture, infection may be determined by the development of cytopathic effect; in eggs or animals, infection may be gauged by virus titer, death, or disease. An example of an end-point dilution assay using cell cultures is shown in Box 2.6, with results expressed as 50% infectious dose (ID₅₀) per milliliter. This type of assay is also suitable for high-throughput applications.

When the end-point dilution assay is used to assess the virulence of a virus or its capacity to cause disease (Volume II, Chapter 1), the result can be expressed in terms of 50% lethal dose (LD₅₀) per milliliter or 50% paralytic dose (PD₅₀) per milliliter, end points of death and paralysis, respectively. The 50% end point determined in an animal host can be related to virus titer, determined separately by plaque assay or other means. In this way, the effects of the route of inoculation or specific mutations on viral virulence can be quantified.