Central nervous system infections are extremely serious. Meningitis affects the membranes surrounding the brain and spinal cord. Encephalitis affects the brain itself.
Viruses that infect the central nervous system (brain and spinal cord) include herpesviruses, arboviruses, coxsackieviruses, echoviruses, and enteroviruses. Some of these infections affect primarily the meninges (the tissues covering the brain and spinal cord) and result in meningitis. Others affect primarily the brain and result in encephalitis. Infections that affect both the meninges and brain result in meningoencephalitis. Meningitis is far more common among children than is encephalitis.
Viruses affect the central nervous system in two ways. They can directly infect and destroy cells in the central nervous system during the acute illness. After recovery from an infection—in the central nervous system or elsewhere in the body—the immune response to the infection sometimes causes secondary damage to the cells around the nerves. This secondary damage (postinfectious encephalomyelitis or acute disseminated encephalomyelitis) results in the child having symptoms several weeks after recovery from the acute illness.
Children acquire infections of the central nervous system through various routes. Newborns can develop herpesvirus infections through contact with infected secretions in the birth canal. Other viral infections are acquired by breathing air contaminated with virus-containing droplets exhaled by an infected person. Arbovirus infections are acquired from bites by infected insects.
The symptoms and treatment of viral meningitis (see see Viral Meningitis) and encephalitis (see see Encephalitis) in older children and adolescents are similar to those in adults. Because the immune system is still developing in newborns and infants, different infections can occur, and infants' inability to communicate directly makes it difficult to understand their symptoms. Usually, however, infants with central nervous system infections have some of the symptoms described below.
Viral central nervous system infections in newborns and infants usually begin with fever. Newborns may have no other symptoms and may initially not otherwise appear ill. Infants older than a month or so typically become irritable and fussy and refuse to eat. Vomiting is common. Sometimes the soft spot on top of a newborn's head (fontanelle) bulges, indicating an increase in pressure on the brain. Because irritation of the meninges is worsened by movement, an infant with meningitis may cry more, rather than calm down, when picked up and rocked. Some infants develop a strange, high-pitched cry. Infants with encephalitis often have seizures or make bizarre movements. Infants with severe encephalitis may become lethargic and comatose and then die. An infection with herpes simplex virus, which is often concentrated in only one part of the brain, may lead to seizures or weakness appearing in only one part of the body.
Postinfectious encephalomyelitis may cause many neurologic problems, depending on the part of the brain that is damaged. Children may have weakness of an arm or leg, vision or hearing loss, mental retardation/intellectual disability, or recurring seizures. These symptoms may not be apparent until the child is old enough for the problem to appear during testing. Often the symptoms resolve with time, but occasionally they are permanent.
Doctors are concerned about the possibility of meningitis or encephalitis in every newborn who has a fever, as well as in an older infant who has a fever and is irritable or otherwise not acting normally. The infants undergo a spinal tap (lumbar puncture—see Fig. 2: How a Spinal Tap Is Done) to obtain cerebrospinal fluid (CSF) for laboratory analysis. In viral infections, the number of lymphocytes (a type of white blood cell) is increased in the CSF, and no bacteria are seen. Immunologic tests that detect antibodies against viruses in samples of CSF may be performed, but these tests take days to complete. Polymerase chain reaction (PCR) techniques are used to identify organisms such as herpesviruses and enteroviruses.
A test of brain waves (electroencephalography—see see Electroencephalography) can be used to help diagnose encephalitis caused by herpesvirus. Magnetic resonance imaging (MRI) and computed tomography (CT) may help confirm the diagnosis. Very rarely, a biopsy (the removal of tissue samples for examination) of brain tissue is needed to determine whether herpesvirus is the cause.
Prognosis and Treatment
Prognosis varies greatly with the type of infection. Many types of viral meningitis and encephalitis are mild, and the child recovers quickly and completely. Other types are severe. Infection with herpes simplex virus is particularly grave. Even with treatment, 15% of newborns with herpes simplex infection of the brain die. If the herpes infection involves other parts of the body as well as the brain, mortality is as high as 50%. Nearly 30% of the survivors have permanent neurologic disability of some kind.
Most infants require only supportive care—they need to be kept warm and given plenty of fluids. Antiviral drugs are not effective for most central nervous system infections. However, infections caused by herpes simplex virus can be treated with acyclovir given by vein.
Last full review/revision May 2007 by Mary T. Caserta, MD