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Viral infections are among the most common illnesses encountered in the ED. Although the majority are trivial, there are certain infections that may be life-threatening, have specific treatments, or have public health implications. This chapter reviews some of the more serious viral infections that cause disseminated illness or have a predilection for the central nervous system (CNS).

Herpesviruses are a class of enveloped DNA viruses that cause a wide variety of human illnesses, ranging from minor, self-limited disease associated with the skin and mucous membranes to severe, life-threatening infection. Herpes-related illnesses may result from primary infection or from reactivation of latent infection, and some may respond to antiviral medications. Most serious illness is found in immunocompromised individuals (see Chapter 149, Human Immunodeficiency Virus Infection and Acquired Immunodeficiency Syndrome, and Chapter 295, The Transplant Patient), but occasionally an unlucky healthy host will suffer severe complications. This chapter reviews infections with the herpesviruses herpes simplex 1 and 2, varicella-zoster virus (VZV), cytomegalovirus (CMV), and Epstein-Barr virus (EBV), as well as selected arboviruses (arthropod-borne viruses).

Herpes simplex virus types 1 and 2 (HSV-1, HSV-2) are closely related double-stranded DNA viruses that commonly cause oral and genital infections and, rarely, devastating CNS disease. Herpes simplex infections are treatable with antiviral drugs, so early recognition of serious infection is important.


HSV is common throughout the world. Transmission occurs when a susceptible individual is exposed to infected secretions. HSV-1 is usually acquired during childhood through nonsexual contact; HSV-2 is almost always sexually transmitted (see Chapter 144, Sexually Transmitted Diseases). HSV-1 seroprevalence varies by socioeconomic status, age, and geographic location. More than 85% of the world’s population is thought to be seropositive for HSV-1.1,2

HSV-1 is one of the most common viral causes of encephalitis in the U.S. It occurs most commonly in patients <20 years and >50 years of age. The mortality rate for untreated disease is >70%.3

Neonates with HSV infection have a high frequency of both visceral involvement and CNS disease. Encephalitis in neonates is most often caused by HSV-2, which is acquired from the maternal genital tract at the time of delivery. The risk is highest when the mother acquires the infection in the third trimester.


Herpes simplex viruses are transmitted through the exchange of saliva, vesicle fluid, semen, and cervical fluid. The virus must come in contact with a mucosal surface or abraded skin, where it replicates and causes localized symptoms before becoming latent in the sensory ganglia. HSV-1 typically resides in the trigeminal ganglia, and HSV-2 is found in the sacral ganglia. Reactivated virus travels to the cutaneous surface and results in localized vesicular eruptions (Figure 148-1).

Figure 148-1.

Herpes simplex virus infection, latency, and recurrence. A. Primary ...

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