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Skin Diseases

Viral Skin Diseases

Viral infections of the skin are widespread, highly contagious, and often recurring, though the most life-threatening are preventable with vaccinations.

Viruses cause numerous skin infections. A common skin lesion called a papilloma is a benign small tumor that grows outward from the skin's surface and is caused by a virus. Warts, or verrucae, are a form of papilloma caused by human papillomaviruses. The infection can be acquired at any age through direct contact between individuals. They are usually self-limited, which means the warts will regress on their own spontaneously within six months to two years. Over 49 different types of papillomavirus can cause warts in humans and have been identified via molecular hybridization and restriction enzyme analyses. Understanding what the papillomavirus type is differentiates not only where on the body these viruses produce lesions, but their cancer-causing potential. For example, papillomavirus types 6 and 11 predominantly cause anogenital warts. Papillomavirus type 16 tends to cause dysplasia, or cellular abnormalities, in the tissue where it grows and has been associated with in situ squamous cell carcinoma. Types 16 and 18 are associated with carcinomas of the uterine cervix.

Molluscum contagiosum is a common, self-limited viral disease of the skin caused by a poxvirus. It is spread via direct contact, particularly in children and adolescents, and during sexual contact. Typically, clusters of small, itchy, umbilicated (having a dimple) papules (skin elevations) appear predominantly on the body trunk or anogenital region.

Herpesviruses are double-stranded DNA viruses, nine types of which have been isolated from humans. These include herpes simplex 1 (HSV-1) and 2 (HSV-2), varicella zoster virus (VZV) (the cause of chickenpox and shingles), cytomegalovirus (CMV), human herpesvirus 6 (HHV-6) (the cause of exanthema subitum, a benign rash in infants), human herpesvirus 7 (HHV-7), Epstein-Barr virus (EBV), and human herpesvirus 8 (HHV-8) (cause of Kaposi sarcoma). HSV-1 and HSV-2 viruses are genetically similar and cause primary and recurrent infections in the skin and mucous membranes. HSV-1 predominantly affects the oropharynx and is a common cause of cold sores. HSV-2 primarily affects the genitals. They cause vesicular lesions in the epidermis and affect the neurons in these locations. In people with normal immune systems, infections resolve on their own in weeks; however, the viruses remain latent or dormant in the nerve cells and can later become reactivated, causing infection again.

The rubeola virus, which is the causative agent of measles, infects as many as 7 million people per year, primarily children who live in low-income countries. Measles is a viral disease the results in blotchy patches of raised blisters on the skin and produces other symptoms such as pneumonia, diarrhea, and inflammation of the cornea. In 2014 alone the World Health Organization reported 115,000 global deaths, mostly of children under age 5, due to measles infection. Measles cases have decreased dramatically in the United States since 1963, when the measles vaccine was introduced, with only 188 cases reported in the United States in 2015. However, measles epidemics still affect unvaccinated individuals and vaccinated individuals who did not develop primary immunity.

The measles virus is an RNA virus of the paramyxovirus family (which includes mumps and respiratory syncytial virus, or RSV) that is spread by respiratory droplets and multiplies in the upper respiratory tract epithelial cells. Viral particles in the blood spread throughout the body and can cause pneumonia, diarrhea, keratitis—inflammation of the cornea—encephalitis, and hemorrhages. Most infected individuals will develop a T cell–mediated immunity that controls the infection and produces the measles rash, which represents a hypersensitivity reaction to viral antigens in the skin. The rash is maculopapular, meaning it is generally flat with some raised patches. It is important to note that the rash does not develop in those people with deficiencies in cell-mediated immunity. The blotchy, reddish-brown rash appears on the face, trunk, and extremities. The rash can last up to seven days, and the virus and other symptoms generally resolve after two to three weeks. There is no treatment for measles. Care is supportive and given in the form of acetaminophen for fever, fluids, and vitamin A supplementation.

Another infectious agent that causes a diffuse rash is the rubella virus, which is a single-stranded RNA togavirus. The virus causes rubella, also known as German measles, and is preventable with vaccination, with a single dose being 95% effective. As a result of vaccination, there are fewer than 10 cases in the United States per year; however, rubella is still a common infection in many parts of the world. The virus is spread through the air via the cough of infected individuals. Rubella causes flu-like symptoms—fever, body aches, fatigue, and joint pain—in addition to a classic maculopapular rash called an exanthem that starts on the face and spreads to the trunk and limbs, resolving after three days. An exanthem is a skin eruption or rash covering most of the exterior of the body that is often associated with viral or streptococcal disease. Rubella can affect anyone of any age, and care is supportive.