Virological Diagnostic Methods

Abstract

Every clinical virologist must step back and ask what the aim of diagnostics is, in general, i.e. the ‘who/ what/ when/ where’ questions. Broadly, the clinical virologists of today must answer a limited set of questions because that is what current technology allows: ● Is this person currently infected with a virus? ● Has this person ever been infected/ exposed to a virus? ● This person has a confirmed virus infection— how is it progressing with or without intervention? ● From whom was this virus infection contracted? However, currently many questions remain remarkably difficult to answer with existing diagnostics. Increasingly the focus of diagnostics is moving from interest solely in the virus itself to how a given virus interacts with a given host pre/ post infection, e.g. HIV host co- receptor testing. Nearly all virological diagnostic methods rely on two fundamental technical principles— target and signal amplification, which both allow the visualization of virus- specific antigen/antibody or nucleic acid. Luckily, some clinical samples, e.g. stool, do not require amplification in order to detect significant virus infections, but even in these situations it is impossible to visualize the presence of viruses or their host antibodies without highly specialized equipment and chemistry. Most viruses are < 200nm in size, and therefore it is impossible to resolve virus particles even with the best optical microscopes. Nearly all of the methodologies detect surrogate markers. It is of note that viable virus numbers do not equal nucleic acid copies, which do not equal virus capsids visible by electron microscopy: these are apples and elephants when trying to compare their quantity. Diagnostic technology operates in two phases or realms; detection or screening, and characterization. For example, asking if a patient has an Influenza A virus infection, followed by asking what is the haemagglutinin/neuraminidase type (e.g. H1N1).