Central nervous system infections caused by viruses can cause meningitis and encephalitis.
Symptoms usually start with fever and can progress to irritability, refusal to eat, headache, neck pain, and sometimes seizures.
The diagnosis of viral central nervous system infections is based on a spinal tap.
Many infections are mild, but others are severe and can cause death.
Antiviral drugs are usually not effective for most viruses that cause central nervous system infections, so children need to receive supportive measures (such as fluids and drugs to control fever and pain).
Some of these infections affect primarily the meninges (the tissues covering the brain and spinal cord) and are called meningitis. Viral meningitis is sometimes called aseptic meningitis. Meningitis can also be caused by bacteria (see Acute Bacterial Meningitis).
Other viral infections affect primarily the brain and are called encephalitis. Infections that affect both the meninges and brain are called meningoencephalitis. Meningitis is far more common among children than is encephalitis.
Viruses affect the central nervous system in two ways:
This later damage (postinfectious encephalomyelitis or acute disseminated encephalomyelitis) typically causes symptoms a few weeks after recovery from the acute illness.
Children acquire viral infections of the central nervous system through various routes. Newborns can develop herpesvirus infections through contact with infected secretions in the birth canal (see Herpes Simplex Virus (HSV) Infection in Newborns). 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 and encephalitis in older children and adolescents are similar to those in adults. The inability of infants 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 when the newborn is upright, 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 other abnormal 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. An infant with herpes simplex virus encephalitis may also have a rash on the skin, in the eyes, or in the mouth. The rash consists of red spots with fluid-filled blisters that crust over or scab before healing (see Herpes Simplex Virus (HSV) Infection in Newborns).
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, difficulty walking, a change in behavior, intellectual disability, or recurring seizures. Some of these symptoms are noticed right away. Other symptoms may not be noticed until later, for example when the child has routine tests of hearing, vision, and/or intelligence. 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 older infants and children who have fever and are irritable or otherwise not acting normally. To make the diagnosis of meningitis or the diagnosis of encephalitis, doctors do a spinal tap (lumbar puncture) to obtain cerebrospinal fluid (CSF, the liquid that surrounds the brain and spinal cord) for laboratory analysis. In viral infections, the number of white blood cells is increased in the CSF, but no bacteria are seen. Immunologic tests that detect antibodies against viruses in samples of CSF may be done, but these tests usually take days to complete. Polymerase chain reaction (PCR) techniques are available to more quickly identify herpesviruses and enteroviruses in the CSF.
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.
Brain infection with herpes simplex virus is particularly grave. Without treatment, about 50% of newborns with herpes simplex infection of the brain die, and about two thirds of those who survive have severe brain damage. Even with treatment, about 25% die and up to half of the survivors have brain damage. If the untreated herpes infection involves other parts of the body as well as the brain, mortality is as high as 85%.
Most children require only supportive care. That is, they need to be kept warm and given plenty of fluids and drugs to treat any fever or seizures. 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.
Postinfectious encephalomyelitis may be treated with corticosteroids or other drugs that lessen the immune response that causes the neurologic damage.