Herpes Virus Transmission


Transmission of Herpes Simplex Viruses

Both Herpes Simplex-1 (HSV-1) and Herpes Simplex-2 (HSV-2) are contracted via contact with the mucosal and abraded skin surfaces. Since HSV-2 is tropic for the genital regions, transmission of HSV-2 is usually through sexual contact. HSV-1, which usually infects the mouth and lips, is usually transmitted via kissing or through the exchange of premasticated food, as in the case of HSV-1 seropositive mothers pre-masticating food for their young children. Following contact, viral replication ensues and infection of either sensory or autonomic nerve endings may occur. Virus, or most likely the nucleocapsid, is transported intraaxonally to the nerve cell bodies in ganglia. HSV-1 has an affinity for the sensory nerve cells in the upper part of the body and thus lies dormant in the cranial nerves. HSV-2 prefers the sensory nerve cells in the genital region and thus lies latent in the dorsal root ganglia located in the lower part of the back. Despite these propensities for certain regions of the body, both herpes simplex viruses can infect other parts of the body.

Transmission of Varicella-Zoster Virus

Transmission of varicella-zoster virus is via direct contact and by the respiratory route. The virus may enter via the conjuctiva, the upper respiratory tract and/or the oropharanx. Once contact is made, the virus replicates at the primary inoculation site and then disseminates via lymphatics and the bloodstream. This eventually results in viremia of the reticuloendothelial system. Such viremia is consistent with the diffuse and scattered nature of chicken pox skin lesions. It can also be verified in some cases by recovery of virus from the blood. The lesions are vesicles that involve both the corium and the dermis, with changes characterized by multinucleated giant cells and ballooning Eventually, the vesicles rupture and release their contents which include infectious virus.

Transmission of Epstein Barr Virus

Epstein Barr is the etiological agent responsible for infectious mononucleosis. Infectious mononucleosis is commonly known as the "kissing disease" because it, like all Epstein Barr diseases, is transmitted primarily via saliva. Epstein Barr Virus (EBV) is not likely to be spread by aerosol or fomites. Because of this, there is little reason to isolate patients with active EBV infection. EBV can also be transmitted by blood transfusion. In industrialized countries, there is a first wave of primary infections before adolescence. A second wave occurs with the onset of social activity associated with adolescence and young adulthood. Primary infection among adolescents accounts for most cases of infectious mononucleosis. Most of the population is EBV-seropositive by adulthood. It should also be noted that most transmission of EBV is due to asymptomatic viral shedding from healthy EBV-seropositive individuals.

EBV has also been implicated as an etiological agent in several human malignancies including B cell lymphomas, nasopharyngeal carcinoma, and Burkitt's lymphoma. Cofactors are thought to play a large role in the development of these diseases.

Transmission of Human Cytomegalovirus

Cytomegalovirus (CMV) may be present in milk, saliva, feces, and urine. Despite the ubiquity of virus in bodily secretions, CMV is usually not spread by casual contact. Rather, it requires long-term intimate exposure. Several of the more common scenarios for contracting CMV are: (1) transmission via sexual contact with a CMV carrier; (2) transmission between young children in day-care centers; (3) transfusion of blood products or organ transplant; and (4) vertical transmission from mother to fetus. Once infected, an individual generally carries the virus indefinately. It is estimated that 80% of the general population is seropositive for CMV. Luckily, CMV infection is almost always asymptomatic in the immunocompetant host. Usually, CMV disease only appears in the immunocompromised host.

Transmission of Human Herpes Virus Type 6

Human herpes virus type six (HHV-6) is the major cause of exanthem subitum, otherwise known as roseola infantum. Exanthem subitum occurs in children aged 6 months to 4 years of age. The disease is benign and is characterized by a high fever and a rash. Because the virus is found in the saliva of more than 90% of all adults, this saliva probably serves as the primary source of transmission.