Herpes simplex virus (HSV) belongs to the group of neurotropic viruses and includes two different genotypes HSV-1 and HSV-2. These typically cause primary and recurrent infections in mucocutaneous crossings. HSV-1 typically affects lips and oral cavity and HSV-2 genitalia. Infections have a variety of clinical manifestations such as vesicles and ulceration. HSV-1 is also a frequent cause of keratoconjunctivitis and corneal blindness caused by it. Both HSV may cause encephalitis with meningitis. Transmission of HSV-2 from mother with a primary infection to the newborn during the birth may lead to a dangerous generalised infection including encephalitis. In patients with malignant tumors and/or immunosuppression may cause disseminated herpetic skin or visceral diseases such as Kaposi's varicelliform eruptions, eczema herpeticum, herpetic oesophagitis, bronchopneumonia and hepatitis.
In the essential features HSV-1 and HSV- 2 have identical virion structure and genome organisation. Virion is composed of the core, icosadeltahedral capsid consisting of 162 capsomers, basicly nonstructured tegument and outer packaging.
Core contains dsDNA genome of the size about 150 kbp with a proportion of G+C 68 % in HSV-1 and 69 % in HSV-2. The genome contains approximately ninety transcription units and is devided into two domains - L (long) and S (short). According the stage of reproduction of the virus in which it leads to their expression it is possible to divide genes for individual proteins into three groups - α - medium early, β - early and γ - late.
The infection occurs through the mucosal epithelium or microinvasion of skin. The virus is reproduced in epithelial cells and spreads through the tissue. After the penetration into the axons of ganglion cells innervating the mucosal epithelium the virus is transported into the body of ganglion cells where it persists in the form of a latent infection. After the reactivation it enters to the productive phase of recurrent infection. Newly matured virions are transported from the ganglion cells and released into the surrounding tissue.
Examination
To distinguish HSV-1 and HSV-2 we use nested multiplex PCR with primers specifically amplifying the part of the gene encoding gpD (glycoprotein inevitable for the entrance of the virus into the cell) in HSV-1 and primers specifically amplifying the part of the gene encoding gpG (glycoprotein conducive releasing of the new particles and dissemination of the virus in the tissue) in HSV-2.
Analytical sensitivity - HSV-1: 4000 copies/ml.
Analytical sensitivity - HSV-2: 4000 copies/ml.
References
- Jain S, Wyatt D, McCaughey C, O'Neill HJ, Coyle PV. Nested multiplex polymerase chain reaction for the diagnosis of cutaneous herpes simplex and herpes zoster infections and a comparison with electronmicroscopy. J Med Virol. 2001;63(1):52-6.
- Fields. Virology (fourth edition). Lippincot Williams & Wilkins, 2001