Viral Diseases at a Glance
- Cutaneous lesions are an extremely common and often the only manifestation of viral infections.
- Viruses can produce skin lesions by direct replication in the epidermis, as is the case with papillomaviruses, poxviruses, and several herpesviruses; or as a secondary manifestation of replication elsewhere in the body.
- The direct effects of viral replication on epidermal cells and the inflammatory immune response both contribute to cutaneous lesions.
- Viral latency followed by reactivation occurs with certain viruses. Neoplastic transformation is possible with some latent viruses.
- Laboratory diagnostic techniques include viral culture, microscopy, detection of viral nucleic acids or viral antigens, and serologic testing.
- Many effective antiviral drugs exist, and others are currently in development.
- Preventive techniques are currently the most effective means for decreasing the morbidity of viral infections. Vaccines are a key component of preventative measures.
Cutaneous manifestations are a prominent feature in many viral infections and may arise from a direct result of viral replication in the epidermis or secondarily from viral replication in other organs. In the latter case, the cutaneous manifestations may be the presenting sign of a systemic infection requiring further evaluation. Although most viral infections with cutaneous involvement are mild and self-limited, occasionally severe or life-threatening complications can develop, especially in immunocompromised hosts. Developments in laboratory testing have improved diagnosis of viral infections in the skin. In addition antiviral medications have improved clinical management and outcomes for many of these viral illnesses. While specific diagnosis of the etiologic viral agent is not always feasible, laboratory diagnosis may also be important epidemiologically. Preventive vaccines are available for certain viruses and are currently the most effective strategy for decreasing morbidity and mortality associated with these diseases. Prophylactic vaccines led to the eradication of smallpox, and now include newer vaccines against herpes zoster virus and human papillomaviruses.
Viruses are unique and fascinating small subcellular agents that require host cells to replicate their genetic material.1 They contain genomic nucleic acid, a protein coat, and some viruses also have a lipid envelope. Lacking functional ribosomes or other organelles, viruses require host cellular machinery for replication of their genetic material.1,2 This dependence on the host cell for transcription and replication is why viruses are often referred to as obligate intracellular parasites. The intracellular location of the virus provides survival benefit to the virus against some of the host's immune mechanisms.
Viruses are an important means of horizontal gene transfer and evolutionary genetic diversity.3,4 Historically, there have been many discussions regarding the etiology and categorization of viruses. Most experts currently view viruses as biological particles that can interact with cells, as opposed to biological organisms or life forms.3 Viruses have features of both of these groups, which accounts for some of their enigma, but lack some of the defining features of living organisms and are not classified taxonomically amongst the kingdoms of life.