encephalitis (en-sef?a-lit'is) [ encephalo- + -itis]
Inflammation of the white and gray matter of the brain. It is almost always associated with meningoencephalitis and may involve the spinal cord (encephalomyelitis). In the U.S. 20,000 cases are reported annually. See: arbovirus
Most cases are caused by viruses: there are about 100 different viral agents that may infect the brain. The disease occurs more often in the very young, the very old, and patients with immune-suppressing illnesses. Mosquito-borne equine arboviruses (or, in some cases, a tick-borne virus) are the most common cause of encephalitis in the U.S. Mosquitoes are infected by feeding on infected birds, which then transmit the virus to humans and animals. Viruses may also be transmitted by inhalation (and passed person to person) or by ingestion of infected goat milk. The West Nile virus (WNV) can cause encephalitis and is related to St. Louis encephalitis (SLE). Encephalitis also occurs as a component of rabies, AIDS, and an aftereffect of systemic viral diseases, e.g., herpesvirus, influenza, measles, German measles, and chickenpox. Central nervous system (CNS) involvement occurs in 15% to 20% of patients with AIDS who develop cytomegalovirus infections. Other organisms causing encephalitis in immunosuppressed patients include fungi (such as Candida, Aspergillus, and Cryptococcus) and protozoa (such as Toxoplasma gondii).
Patients present with a wide variety of neurological symptoms, depending on the infected region of the brain and the type and amount of damage the organism has caused. Sudden onset of fever with headache and vomiting may be the first symptoms. These progress to stiff neck and back (meningeal irritation) and to signs of neuronal damage: drowsiness, seizures, tremors, ataxia, cranial nerve paralysis, abnormal reflexes, and muscle weakness and paralysis are common. Personality changes and confusion usually appear before the patient becomes stuporous or comatose. Coma may persist for weeks after the acute phase of illness.
The diagnosis is based on clinical presentation, culture and examination of blood and cerebrospinal fluid, and computerized tomography (CT) scan or magnetic resonance imaging (MRI) results.
Acyclovir is given for herpes simplex virus infection, the only common viral pathogen for which there is effective treatment. Survival and residual neurological deficits appear to be tied to mental status changes before acyclovir therapy begins. Rabies is treated with rabies immune globulin and vaccine. If the infection is bacterial, antibiotics are used. For other viruses, treatment focuses on supportive care and control of increased intracranial pressure (ICP) using osmotic diuretics, e.g., mannitol), corticosteroids, and drainage.
The acutely ill patient's mental status, level of consciousness, orientation, and motor function are assessed for indications of increasing ICP and documented to monitor changes. The head of the bed is raised slightly to promote venous return; neck flexion is contraindicated. Sedatives help to control restlessness; aspirin or acetaminophen reduces fever and relieves headache. Measures to prevent stimuli that increase ICP are implemented, e.g., preoxygenating with 100% oxygen before suctioning, preventing isometric muscle contraction, using diet and stool softeners to minimize straining at stool, and using turning sheets and head support when turning the patient. Fluid intake should be adequate to prevent dehydration, but overload must be avoided to prevent further cerebral edema. Fluid balance and weight are monitored daily. Adequate nutrition should be maintained with small, frequent meals or enteral or parenteral feeding as necessary. Frequent oral care should be provided. Passive and/or active range-of-motion exercises and resistive exercises to prevent contractures and maintain joint mobility and muscle tone are used as long as they do not increase ICP.
Normal supportive care is provided in a quiet environment, with lights dimmed to ease photophobia, with no shadows, which increase the potential for hallucinations. Emotional support and reassurance should be provided and the patient reoriented if delirium or confusion is present. Behavioral changes that occur with encephalitis usually fade as the acute phase passes, but rehabilitation programs are necessary for the treatment of residual neurological deficits. Public health preventive measures include controlling standing water that provides mosquito breeding sites and insecticide spraying to kill larvae and adult mosquitoes. Public education should focus on reducing outdoor time during early morning and early evening hours, wearing appropriate covering clothing when exposure is unavoidable, and use of insect repellents containing DEET.
acute disseminated encephalitisPostinfectious encephalitis.
Australian encephalitisMurray Valley encephalitis.
Bickerstaff brainstem encephalitis See: Bickerstaff brainstem encephalitis
California (La Crosse) virus encephalitis
A viral encephalitis that is the most common mosquito-borne illness in the U.S. It typically affects children in summer or early fall, largely in the Middle Atlantic or midwestern states, causing fever, headache, seizures, and localized muscle paralysis. The primary vector is Aedes triseriatus. A full recovery usually follows the illness.
Encephalitis of only the brain cortex.
Cree encephalitisAicardi-Goutières syndrome.
eastern equine encephalitis
Encephalitis caused by the eastern equine arbovirus, which is transmitted from horses to humans by mosquitoes; the incubation period is 1 to 2 weeks. Although this is the least common of the arboviruses, mortality is approx. 25%, and those who survive often have neurological problems. In the U.S. it occurs on the East Coast, Gulf Coast, and in the Great Lakes region during the mosquito season from midsummer to early fall.
Any form of encephalitis that occurs as an epidemic.
Encephalitis caused by either the western or the eastern equine arbovirus, which is carried by mosquitoes from horses. The disease ranges from mild to fatal.
Herpes encephalitis in which there is hemorrhage with brain inflammation.
Encephalitis caused by infection of the brain with herpes simplex virus-1 (or, less often, herpes simplex virus-2). This relatively common form of encephalitis typically involves the inferior surfaces of the temporal lobes and may cause hemorrhagic necrosis of brain tissue. It is fatal in at least one third of all cases. Acyclovir (or an analog) is used to treat the infection.
Acute encephalitis without suppuration.
Encephalitis that occurs in infants. The most common agents are arboviruses and herpes simplex virus.
Japanese (B type) encephalitis Abbreviation: JE
Encephalitis caused by the Japanese B type arbovirus, an infection carried by swine. It occurs sporadically in Japan, Taiwan, China, and Korea and is controlled by vaccine.
Encephalitis due to lead poisoning.
A form of encephalitis that occurred frequently after the influenza pandemic of 1917–1918, but rarely since. Its hallmarks include paralysis of oculomotor function and marked sleepiness or coma. Survivors developed a parkinsonism-like illness. Synonym: Economo disease
Murray Valley encephalitis
An epidemic viral encephalitis originating in Murray Valley, Australia. Synonym: Australian encephalitis
A form of encephalitis occurring within the first several weeks of life.
paraneoplastic limbic encephalitis Abbreviation: PNLE
A brain disorder occurring in some patients with cancer, characterized by the rapid onset of memory loss, often with temporal lobe disease, seizures, delirium, or disturbances of mood. Patients with PNLE often have antibodies against tumor antigens that also react with nerve cell antigens. In some patients the neurological disorder improves after treatment of the responsible tumor.
Inflammation of the white matter of the cerebrum, occurring mainly in the young.
Encephalitis that follows a systemic viral infection (such as mumps or measles) or a reactivation to varicella-zoster in adults. Synonym: acute disseminated encephalitis
Acute encephalitis after vaccination.
Encephalitis characterized by abscesses in the brain.
raccoon roundworm encephalitis
Encephalitis characterized by inflammation of the meninges, eosinophilia, prolonged encephalopathy, retinitis, and delayed recovery with profound neurological deficits. It is transmitted to children (or others) who eat soil contaminated by raccoon feces.
Rasmussen encephalitis See: Rasmussen encephalitis
Russian spring-summer encephalitis
Encephalitis due to a tick-borne virus. Humans may also contract it by drinking goat milk.
St. Louis encephalitis
Encephalitis caused by the St. Louis arbovirus and carried by mosquitoes. It emerged during an epidemic in the summer of 1933 in and around St. Louis, Missouri. Now endemic in the U.S. (esp. Florida), Trinidad, Jamaica, Panama, and Brazil, it occurs most frequently during summer and early fall.
A flaviviral infection of the brain transmitted by Ixodes ticks.
Encephalitis resulting from metal poisonings, e.g., lead poisoning.
western equine encephalitis
A mild type of viral encephalitis that has occurred in the western U.S. and Canada.
inflammation of the brain. Changes in vessel walls, as well as of nervous tissue, are almost a constant feature of encephalitis.
There are many types of encephalitis, depending on the causative agent and the structures involved. A large percentage of the cases are caused by viruses, some of them, e.g. equine encephalomyelitis, being transmitted from animals to humans. Clinically encephalitis is characterized by initial signs of nervous irritation including muscle tremor, excitement and convulsions, followed by a stage of loss of function characterized by weakness, paralysis, coma and death. The more acute and serious symptoms may include fever, delirium, convulsions, coma, and, in a significant number of patients, death.
Many encephalitides are accompanied by involvement of the spinal cord and are more correctly classified as encephalomyelitides. See also encephalomyelitis
The etiologically or geographically specific diseases are listed under their specific titles. Human pathogens which sometimes infect animals include Central European, Far Eastern Russian tick-borne encephalitides, Omsk hemorrhagic fever, Kyasanur forest disease. Viruses isolated from asymptomatic cases of encephalomyelitis include Kunjun virus.
acute disseminated encephalitis
a group of viral encephalitides of humans in which animals play some epidemiological part. See togaviridae
canine distemper encephalitis
a demyelinating encephalitis, most severe in the cerebellum and optic tracts, is a feature of infection by canine distemper virus.
seen in certain viral infections, e.g. canine distemper, caprine arthritis-encephalitis and visna of sheep.
equine herpesvirus encephalitis granulomatous encephalitis Israeli turkey encephalitis Japanese B encephalitis
believed to be primarily a disease of birds that are the source of infection for animals, including humans, pigs and horses. Transmission is by mosquito. Affected horses show a wide variety of signs including incoordination, excitability and blindness. Most cases recover. Ruminants show little clinical effect. Pigs are a major source of virus and extensive losses occur by way of encephalitis in young pigs and abortion and stillbirth in adult sows.
Murray Valley encephalitis
there is tentative evidence of clinically inapparent infection of horses in Australia with this flavivirus virus during an epidemic of the disease in humans.
Nipah virus encephalitis
occurred on the Malaysian peninsula as an epidemic in pig farmers. Pigs are the source of the virus which has antigenic relationship to Hendra virus.
old dog encephalitis
a chronic, progressive, sclerosing panencephalitis in mature dogs; characterized by motor and mental deterioration, blindness, pacing and circling. Believed to be caused by distemper virus, but there are distinct differences from distemper encephalitis.
an acute disease of the central nervous system seen in patients convalescing from infectious, usually viral, diseases.
acute encephalitis sometimes occurring after vaccination, mediated by immune mechanisms.
a tick-borne flavivirus disease of humans with serological but no clinical evidence of infection in nearby goats.
Ross River encephalitis
there is tentative evidence of clinically inapparent infection of horses in Australia with the causative mosquito-borne alphavirus virus of this human disease.
Russian spring-summer encephalitis
a similar and probably identical disease to the flavivirus that causes louping ill of sheep, occurring in central Europe. It is a disease of humans occurring in epidemics related to the prevalence of vector ticks in forests where the disease is most common. Lesions are present in organs other than the brain. The severity varies from mild to fatal.
St. Louis encephalitis
an arthropod-borne flavivirus infection, first observed in 1932 in Illinois. It is a serious pathogen of humans, but does not cause disease in animals.