In this article we will discuss about Herpes Virus:- 1. Introduction to Herpes Virus 2. Classification of Herpes Virus 3. Herpes Simplex Virus.
Introduction to Herpes Virus:
Herpes viruses (100 nm in diameter) contain icosahedral capsid made of 162 capsomeres, DNA genome and are surrounded by a lipid envelope. Electron microscope cannot distinguish different members of Herpes virus. Because of their multiplication in the nucleus of cell, they produce Cowdry type A inclusion body (Fig. 58.1).
Classification of Herpes Virus:
Herpes viruses are divided into 3 subfamilies on the basis of their biological properties. Both man and animals are affected. Antigenically, they differ from each other except Herpes simplex types 1 and 2—which share common antigens.
Human B-lymphotrophic virus, a new virus designated as human herpes virus type 6, has been recovered from lymphoproliferative disordered patients. Herpes viruses frequently cause recurrent infection.
Herpes Simplex Virus:
It infects only humans. Herpes virus type 1 causes oral and ocular lesions, whereas Herpes virus type 2 causes genital infection; congenital malformation may occur due to trans-placental passage of both types of Herpes virus.
Pathogenesis of Herpes Virus:
The primary mode of entry is through the skin, oral mucosa, or eyes. It may result into a vesicle formation under the layer of keratinized squamous epithelial cells. The vesicle fluid contains multinucleated giant cells and eosinophilic intra-nuclear inclusion with inflammatory cells and cellular debris. The virus infects draining lymph nodes causing lymphadenitis which may heal with little soon.
After primary infection the virus travels by retrograde intra-axonal flow to sensory root ganglia which innervate the area of infection. They settle with the neurons (trigeminal, sacral). The Herpes virus DNA gets integrated in the host cell genome.
(1) Initial (primary) infection due to type 1 is mostly acquired at 6 months to 3 years of age through eye or oral mucosa; it is often asymptomatic; only 10-15% of infected children show acute gingivo stomatitis. About 75% of adults harbour antibodies against these viruses.
Saliva, skin lesions, or oropharyngeal lesions of patients or carriers. Recurrent infections are common (e.g. recurrent herpes labialis) and may lead to dendritic keratitis, corneal ulcers, acute keratoconjunctivitis vesicles on eyelids. The transmission of type 1 virus is by direct contact or droplet spreads. Type 1 virus may also produce eczema herpeticum (crops of vesicles on the body) and encephalitis.
2. Sexual transmission is common in genital infection due to types 1 and 2 virus. Neonate may be infected from mother’s birth canal. Lesions are common in the penis and urethra of male; cervix, vulva, vagina and perineum of the female.
3. The causal relation of type 2 virus in cervical and valvular carcinoma is yet to be evaluated. Patients with these malignancies show high titre HSV-2 type antibody.
Immunity:
Type 1 antibodies appear in early childhood. Type 2 antibodies during adolescence.
Clinical Diagnosis is Important:
1. Smear from the base of the vesicle is stained by toluidine blue. Multinucleated giant cells and cowdry type A intra-nuclear inclusion bodies can be seen.
2. Herpes virus can be grown in human embryonic tissue, HeLa cells or in chorioallantoic membrane (CAM) of chick embryo.
3. Serological tests (CFT, neutralisation test) are positive.