practical virology

Lab / Medical Virology

Viral structure:
Viruses are composed of a nucleic acid genome surrounded by a protein coat called a capsid-togather the genome and capsid are referred to as the nucleocapsid. Genomes are either RNA or DNA. Viral capsid are composed of many individual subunits called capsomeres. Capsomeres assemble into an icosohedral or irregular-shapped capsid usually assume a helical form. Some of the larger viruses have a lipid containing envelope that surrounds the capsid. In addition, many viruses have glycoprotein spikes that extend from the surface of the virus, acting as attachment projections or as enzymes.

Specimen Selection and Collection:

Specimen selection depends on the specific disease syndrome, viral etiologies suspected and time of year.

1.Throat, nasopharyngeal swab or aspirate: Throat swabs are acceptable for recovering enteroviruses, adenoviruses and HSV, whereas nasopharyngeal swab or aspirate specimens are preferred for the detection of influenza and parainfluenza viruses. Throat specimens are collected by rubbing inflamed, vesiculated, or purulent areas of the posterior pharynx with a dry, sterile swab. Nasopharyngeal secretion specimens are collected by inserting a swab with flexible shaft through the nostril to the nasopharynx.

2.Rectal swabs and stool specimens: Used to detect rotavirus, enteric adenoviruses and enteroviruses. Rectal swabs are collected by inserting a swab (3-5) cm into the rectum to obtain feces.

3.Urine: CMV, mumps, rubella, measles, polyomaviruses and adenoviruses can be detected in urine. Virus recovery may be increased by processing multiple (2-3) specimens because virus can be shed intermittently or in low numbers. The best specimen is at least (10 ml) of a clean-voided first-morning urine.

4.Blood: Used to detect CMV, HSV, enterovirus and adenoviruses. (50-10 ml) of anticoagulated blood collected in a vacutaner tube is needed.

5.Tissue: Useful for detecting viruses that infect lung (CMV, influenza virus, adenovirus), brain (HSV), and gastrointestinal tract (CMV). Specimens are collected during surgical procedures.