is an acute inflammation of the
Brain , commonly caused by a
Viral Infection . Sometimes, encephalitis can result from a
Bacteria l infection, such as bacterial
Meningitis , or it may be a complication of other infectious diseases like
Rabies (viral) or
Syphilis (bacterial). Certain
Parasitic Protozoa l infestations, like by
Toxoplasma , can also cause encephalitis in people with compromised immune systems. Brain damage occurs as the inflamed brain pushes against the skull, and, depending on its severity, can lead to death.
Patients with encephalitis suffer from
Fever ,
Headache , vomiting, confusion, drowsiness and
Photophobia . The patients could also suffer from weakness, seizure, and less commonly, stiffness of the neck. Rarely, the patients may have limb stiffness, slowness in movement and clumsiness, depending on the specific part of the brain involved. The symptoms of encephalitis are caused by the brain's defense mechanisms activating to get rid of the infection, including swelling, small bleedings and cell death.
Victims are usually exposed to viruses resulting in encephalitis by insect bites or food and drink. The most frequently encountered agents are
Arbovirus es (carried by
Mosquito es or
Tick s, see also
Tick-borne Meningoencephalitis ) and
Enterovirus es (
Coxsackievirus ,
Poliovirus and
Echovirus ). Some of the less frequent agents are
Measles ,
Rabies ,
Mumps ,
Varicella and
Herpes Simplex viruses. Incidentally type 3 Lyssavirus (
Mokola Virus ), found in Australia, causes a lethal encephalitis which hardly resembles rabies. Numerically, the most important cause of encephalitis worldwide is probably Japanese encephalitis, as it causes up to 50 000 cases a year, with about 15 000 deaths.
Japanese Encephalitis affects East and Southeast
China ,
Korea ,
Japan ,
Taiwan , Southeast Asia,
Papua New Guinea , South Asia and even Northern
Australia . The most widespread cause of encephalitis worldwide, however, is Herpes Simplex encephalitis. The herpes simplex virus causes inflammation on the temporal lobe of the brain, and if not treated, half to three quarters of the patients succumb. In very young children, however, the virus could affect any part of the brain, even sparing the temporal lobe.
An interesting cause of viral encephalitis is the
Nipah Virus . It was first discovered in Malaysia in 1998. A virus from the same genus, the Hendra virus, was discovered in September 1994 in northern
Australia when 13 horses and their owner died.
Adult patients with encephalitis present with acute onset of fever, headache, confusion, and sometimes seizures. Younger children or infants may present with irritability, anorexia and fever.
Neurologic examination usually reveal a drowsy or confused patients. Stiff neck, due to the irritation of the meninges covering the brain, indicates that the patient has either meningitis or meningoencephalitis. Examination of the
Cerebrospinal Fluid obtained by a
Lumbar Puncture procedure usually reveals increased amounts of proteins and white blood cells with normal glucose, though in a signficant percentage of patients, the cerebrospinal fluid may be normal. CT scan is often not helpful, as cerebral abscess is uncommon. Cerebral abscess is commoner in patients with meningitis rather than encephalitis. Bleeding is also uncommon except in patients with herpes simplex type 1 encephalitis. Magnetic resonance imaging offers better resolution. In patients with herpes simplex encephalitis, electroencephalograph may showed sharp waves in one or both of the temporal lobes. Lumbar puncture procedure is performed only after the possibility of prominent brain swelling is excluded by a CT scan examination. Diagnosis is often made with detection of antibodies against specific viral agent (such as herpes simplex virus) or by polymerase chain reaction that amplifies the RNA or DNA of the virus responsible.
Treatment is usually
Symptomatic . Reliably tested specific antiviral agents are available only for a few viral agents (e.g.
Aciclovir for herpes encephalitis) and are used with limited success for most infection except herpes simplex encephalitis. In patients who are very sick, supportive treatment, such as mechanical ventilation, is equally important.
Encephalitis Lethargica is an atypical form of encephalitis which caused an
Epidemic from 1917 to 1928. There have only been a small number of isolated cases since, though in recent years a few patients have shown very similar symptoms. The cause is now thought to be a bacterial agent or an autoimmune response following infection. As depicted in the book ''
Awakenings '' by doctor
Oliver Sacks , which was made into the film starring
Robin Williams and
Robert De Niro , the disease sometimes caused
Catatonia which could persist for decades.
