Varicella-zoster virus is the causative organism of both varicella (chickenpox) and herpes zoster (shingles). It is extremely contagious; prior to routine vaccination, it was usually acquired in childhood.
Varicella occurs year round, but there is a higher incidence during winter and spring months. The infection rate ranges from 60% to 100% in exposed individuals. The introduction of the varicella vaccine to routine childhood immunizations in 1995 has dramatically reduced the clinical burden of the virus.8
Herpes zoster can occur once immune response against the virus wanes, usually with advancing age. Over 90% of adults have serologic evidence of varicella-zoster virus infection, and unvaccinated persons who live to 85 years of age have a 50% risk of herpes zoster.9 Iatrogenic immune suppression, certain diseases such as lymphoproliferative disorders, human immunodeficiency virus infection, and organ transplantation increase the risk of herpes zoster.
Vaccines are available to prevent both chickenpox and herpes zoster, although neither is 100% effective. Encourage parents to vaccinate their children, and remind those age 60 or older about the availability of a vaccine to prevent herpes zoster. Varicella-zoster immune globulin is available, but its use is generally limited to postexposure prophylaxis for nonimmune pregnant women and the severely immunosuppressed. Healthy individuals who are not immune can be vaccinated after exposure. Exposed individuals should be watched closely, and antivirals should be given to high-risk patients if they develop symptoms.10
Varicella-zoster virus spreads to the respiratory mucosa of a susceptible host via aerosolized droplets of respiratory secretions of patients with chickenpox. It can also spread from direct contact with vesicle fluid in herpes zoster but is not as highly contagious in this situation. The virus multiplies in regional lymph nodes and then disseminates to the nasopharyngeal surfaces and the skin, causing the characteristic rash. It is contagious until all the lesions have crusted over. Varicella-zoster virus remains latent in the dorsal root ganglion and can later reactivate along dermatomes, resulting in shingles (Figure 153–6).
Primary infection, latency, and reactivation of varicella-zoster virus. A. Generalized distribution of primary varicella. B. Latent phase. C. Reactivation phase of clinical herpes zoster. [Reproduced with permission from Wolff K, Johnson RA: Fitzpatrick's Color Atlas and Synopsis of Clinical Dermatology, 6th ed., © 2009 by McGraw-Hill, Inc., New York.]
VARICELLA CLINICAL FEATURES
Varicella (chickenpox) is a febrile illness with a vesicular rash. Often it is associated with nonspecific symptoms of headache, malaise, and loss of appetite. The rash is superficial and appears in crops, so patients typically have lesions at varying stages, including papules, vesicles, and crusted lesions (Figure 153–7). Lesions are concentrated more on the torso and face and typically crust and slough off after 1 to 2 weeks. Most infections are minor and self-limited. Immunized patients can occasionally develop mild chickenpox.
Rash of primary varicella (chickenpox), demonstrating lesions of multiple stages, including papules, vesicles, and crusted lesions. [Reproduced with permission from Wolff K, Johnson RA: Fitzpatrick's Color Atlas and Synopsis of Clinical Dermatology, 6th ed., © 2009 by McGraw-Hill, Inc., New York.]
A range of complications can occur, more often in those at extremes of age or the immunocompromised. Bacterial superinfections of skin lesions, most often with group A streptococci, can cause serious illness including necrotizing fasciitis. Children with lymphoma and leukemia may develop progressive varicella in which vesicles continue to erupt into the second week of illness, sometimes with visceral involvement of the lung, liver, and brain. CNS complications such as cerebellar ataxia, meningitis, meningoencephalitis, and vasculopathy are well described. Pneumonitis can be severe and is more common in pregnant women.8
HERPES ZOSTER CLINICAL FEATURES
Herpes zoster (shingles) often begins with a prodrome of malaise, headache, and photophobia. The patient notes pain, itching, and paresthesias in one or more dermatomes. These symptoms are followed by the development of a maculopapular rash that becomes vesicular. The eruption does not cross the midline (Figure 153–8). Most commonly, herpes zoster affects the chest or face, but it can affect any dermatomal level. Herpes zoster ophthalmicus can cause blindness and is the result of reactivation along the ophthalmic distribution of the trigeminal nerve (see chapter 241, "Eye Emergencies"). The seventh cranial nerve can be involved, causing facial nerve paralysis and lesions along the auditory canal (herpes zoster oticus). Postherpetic neuralgia, pain that persists for >30 days, is a feared complication. The incidence increases with advancing age, and pain may last months or years.
Dermatome distribution of the classic rash of herpes zoster (shingles).
Dissemination of varicella-zoster virus can occur in immunocompromised patients. Herpes zoster involving more than three dermatomes is often a clue to an immunodeficient condition. The presence of herpes zoster in a young, healthy person may be a sign of human immunodeficiency virus infection. In many cases of disseminated disease, the skin is the only involved structure. However, the virus may spread to the visceral organs and cause pneumonitis, hepatitis, and encephalitis.
Varicella-zoster virus infections have a characteristic appearance, so a clinical diagnosis is sufficient in most cases. Clinicians should look for the characteristic rash of chickenpox, which involves vesicles that appear in crops in different stages of development. Herpes zoster is diagnosed when clusters of vesicles and papules appear in a dermatomal pattern.
Laboratory diagnosis is needed in patients with atypical illness or severe disease. This is accomplished through viral culture, antigen testing, or polymerase chain reaction testing of vesicle fluid. Although smallpox has been eradicated, it remains a potential threat as a biologic weapon, and the lesions could be confused with those of varicella. The lesions of smallpox are larger and distributed more on the extremities, and all lesions are at the same stage of development.
Obtain a chest radiograph if pneumonitis is suspected. An MRI of the brain, lumbar puncture, and polymerase chain reaction testing for varicella-zoster virus are appropriate for suspected brain involvement.
Most healthy patients need only supportive care for chickenpox. Acyclovir and similar antiviral agents decrease the number of lesions and shorten the course if therapy is started within 24 hours of rash onset. However, the impact of treatment is modest, so it is not routinely recommended for those who are otherwise healthy. Secondary skin infections are typically caused by group A streptococci and can be treated with a first-generation cephalosporin.
Consider acyclovir for those at higher risk for complications, including adults and children >12 years of age, patients with chronic skin or pulmonary disorders, those receiving long-term salicylate therapy, and immunocompromised patients. Varicella-zoster virus is less sensitive to acyclovir than herpesvirus and requires higher and more frequent dosing. Although chosen by some for dosing simplicity, famciclovir and valacyclovir are not licensed for the treatment of varicella (chickenpox) in the United States.
Antiviral agents hasten lesion resolution, reduce new lesions, reduce viral shedding, and decrease acute pain, but do not reduce the severity of postherpetic neuralgia.9 Using antiviral therapy in immunocompromised patients may reduce the risk of severe disseminated disease. Start antiviral medication within 72 hours of the onset of rash, and consider treatment at >72 hours if new vesicles are still present or developing. Treat immunocompromised patients regardless of the time since rash onset. Benefits are more pronounced in patients >50 years of age. Therapy is well tolerated, and the risk of adverse events is minimal.
Treat those with disseminated herpes zoster, those with CNS involvement, and severely immunosuppressed patients with herpes zoster with IV acyclovir. Use valacyclovir in those with herpes zoster ophthalmicus, along with ophthalmologist consultation (see chapter 241, "Eye Emergencies").
Herpes zoster can be extremely painful and require opioid analgesia. Corticosteroids in combination with antivirals may provide a modest decrease in acute pain but do not decrease the development of postherpetic neuralgia.9 Adjunctive corticosteroids can be considered in older individuals with severe pain who do not have contraindications to their use.