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
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).
Herpes simplex virus infection, latency, and recurrence. A. Primary
infection. B. Latent ...