ABSTRACT
Viruses, that use the ultimate and most successful form of parasitism known, contribute significantly to human morbidity and mortality globally. Besides causing sporadic, endemic and chronic infections, they are also notorious for leading to outbreaks and pandemics. This chapter discusses the general principles underlying the laboratory diagnosis of viral infections. The most important step in their diagnosis is appropriate specimen collection and transport, since the performance of diagnostic tests is strongly influenced by the quality of the sample submitted. Direct microscopy is an important diagnostic tool, and can provide important clues to viral diagnosis. Antigen detection tests provide direct evidence of a viral pathogen in the sample. Serological tests for virus-specific IgM or IgG provide indirect evidence (host immune response) to a virus, and are also useful in ascertaining their epidemiology. Virus isolation has its advantages, but requires expertise and is available only in few reference laboratories. The advent of molecular techniques like PCR has totally changed the face of diagnostic virology. Quantification of viral nucleic acid by real time PCR is useful in the management and prognostication of diseases caused by viruses like HIV-1, HBV, HCV and CMV. Other molecular techniques indicated in the management of certain viral infections include viral genotyping and anti-viral drug resistance testing.
