Assays for virus infection

Abstract

Abstract The laboratory diagnosis of virus infections utilizes a wide range of techniques, including virus isolation (Chapter 2), the detection of virus antigens and specific antiviral antibodies and the amplification and detection of virus genomes. This chapter will outline the principal methods used for the diagnosis of virus infections, and describe in detail those which are used most commonly. This section will outline methods used to identify and quantify viruses grown in cell culture, since detailed methods for the isolation of viruses are described in Chapter 2. Many of the cytopathic effects (CPE) seen in virus-infected cell cultures are characteristic of specific viruses or virus groups (Table 1), and the ability to recognize a specific CPE is the important first step in virus identification. Not all viruses growing in cell culture produce a CPE, and other methods have been devised for their identification (Section 2.7). The object of these assays is to measure the number of infectious particles in a suspension of viruses. This is done either by plaguing viruses on monolayer cell cultures in order to reveal and enumerate plaques which originate from a single infectious virus particle (pfu) (Protocol I), or by determining the highest dilution of the virus suspension which produces a CPE in 50% of the cell cultures inoculated (TCID50) (Protocol 2). The TCID50 value is calculated by use of the Reed-Muench formula or the Karber method (1). Calculation of the TCID50 is more commonly used to determine the dose of virus required in a neutralization test, although plaque assays give a more precise measurement of virus infectivity.