There are a number of clinical situations where viral diagnosis may be particularly helpful. These include:
Viral diseases in which there are important public health considerations (e.g., influenza and arbovirus encephalitis)
Viral diseases in which there are significant risks to susceptible persons exposed to the patient (e.g., measles, hepatitis B, and varicella)
Situations involving important prognostic considerations (e.g., congenital infections, encephalitis, and infections in immunocompromised hosts).
Situations where withdrawal of antibiotics might serve the patient’s interest (e.g., respiratory virus infections and viral meningitis)
Situations where therapeutic action depends on viral diagnosis (e.g., treatment with an antiviral agent, hospital infection control, and therapeutic abortion for rubella in pregnancy).
Cases where a viral diagnosis will teach the medical staff important lessons about diseases or epidemiology and improve subsequent care of similar patients.
In order to identify the range of suspected viruses in any one individual patient, the onus is on the clinician to provide comprehensive information and/or liaise with laboratory staff.
Viruses can be studied in a number of direct and indirect ways and all these methods can be applied in a diagnostic situation, ie. is this patient/animal infected with a particular virus? There are two approaches:
1. Direct method (approach) – detection and demonstration of the virus itself or its products; and
-Virus isolation (Gold standard) – growth of virus or virus culture (Viral replication can be detected by : Cytopathic Effect, Hemadsorption, and Virus Interference).
-Direct visualization – whole virus (Example the use of Electron Microscopy)
-Detection of viral antigens – proteins (Example the use immunostaining and agglutination techniques)
-Detection of viral nucleic acids – genetic material (Examples the use of PCR and Probe-hybridization techniques, DNA sequencing and blotting techniques).
2. Indirect method (approach)- detecting the host’s response to the virus (detecting antibodies)
-Serological Assays – antibody detection (Example the use binding assays like ELISA, immunobinding assays like western blot, functional assays like virus neutralization test, and agglutination assays like Hemagglutination inhibition assay).
The details for each techniques/method/test will be covered under separate topics