Encephalitis is an acute
inflammationInflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
of the
brainThe human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
. Encephalitis with
meningitisMeningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...
is known as
meningoencephalitisMeningoencephalitis is a medical condition that simultaneously resembles both meningitis, which is an infection or inflammation of the meninges, and encephalitis, which is an infection or inflammation of the brain.-Causes:...
. Symptoms include
headacheA headache or cephalalgia is pain anywhere in the region of the head or neck. It can be a symptom of a number of different conditions of the head and neck. The brain tissue itself is not sensitive to pain because it lacks pain receptors. Rather, the pain is caused by disturbance of the...
,
feverFever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...
,
confusionConFusion is an annual science fiction convention organized by the Stilyagi Air Corps and its parent organization, the Ann Arbor Science Fiction Association. Commonly, it is held the third weekend of January. It is the oldest science fiction convention in Michigan, a regional, general SF con...
, drowsiness, and fatigue. More advanced and serious symptoms include
seizureAn epileptic seizure, occasionally referred to as a fit, is defined as a transient symptom of "abnormal excessive or synchronous neuronal activity in the brain". The outward effect can be as dramatic as a wild thrashing movement or as mild as a brief loss of awareness...
s or convulsions, tremors, hallucinations, and memory problems.
Viral
Viral encephalitis can occur either as a direct effect of an acute infection, or as one of the sequelae of a latent infection. The most common causes of viral encephalitis are
rabies virusThe rabies virus is neurotropic virus that causes fatal disease in human and animals. Rabies transmission can occur through the saliva of animals....
,
Herpes simplexHerpes simplex is a viral disease caused by both Herpes simplex virus type 1 and type 2 . Infection with the herpes virus is categorized into one of several distinct disorders based on the site of infection. Oral herpes, the visible symptoms of which are colloquially called cold sores or fever...
,
poliovirusPoliovirus, the causative agent of poliomyelitis, is a human enterovirus and member of the family of Picornaviridae.Poliovirus is composed of an RNA genome and a protein capsid. The genome is a single-stranded positive-sense RNA genome that is about 7500 nucleotides long. The viral particle is...
, measles virus, and
JC virusThe JC virus or John Cunningham virus is a type of human polyomavirus and is genetically similar to BK virus and SV40. It was discovered in 1971 and named using the two initials of a patient with progressive multifocal leukoencephalopathy...
. Other causes include infection by
flavivirusFlavivirus is a genus of the family Flaviviridae. This genus includes the West Nile virus, dengue virus, tick-borne encephalitis virus, yellow fever virus, and several other viruses which may cause encephalitis....
es such as St. Louis encephalitis virus or
West Nile virusWest Nile virus is a virus of the family Flaviviridae. Part of the Japanese encephalitis antigenic complex of viruses, it is found in both tropical and temperate regions. It mainly infects birds, but is known to infect humans, horses, dogs, cats, bats, chipmunks, skunks, squirrels, domestic...
, or by
TogaviridaeThe Togaviridae are a family of viruses, including the following genera:* Genus Alphavirus; type species: Sindbis virus, Eastern equine encephalitis virus, Western equine encephalitis virus, Venezuelan equine encephalitis virus, Ross River virus, O'nyong'nyong virus, Chikungunya* Genus Rubivirus;...
such as
Eastern equine encephalitis virusEastern equine encephalitis virus , commonly called sleeping sickness or Triple E, is a zoonotic alphavirus and arbovirus present in North, Central and South America and the Caribbean. EEE was first recognized in Massachusetts, USA in 1831 when 75 horses died of encephalitic illness...
(EEE virus),
Western equine encephalitis virusThe Western equine encephalomyelitis virus is the causative agent of relatively uncommon viral disease Western equine encephalomyelitis . An Alphavirus of the family Togaviridae, the WEE virus is an arbovirus transmitted by mosquitoes of the genera Culex and Culiseta...
(WEE virus) or
Venezuelan equine encephalitis virusVenezuelan equine encephalitis virus is a mosquito-borne viral pathogen that causes Venezuelan equine encephalitis or encephalomyelitis . VEE can affect all equine species, such as horses, donkeys, and zebras. After infection, equines may suddenly die or show progressive central nervous system...
(VEE virus).
Bacterial and other
It can be caused by a
bacteriaBacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
l infection, such as bacterial
meningitisMeningitis is inflammation of the protective membranes covering the brain and spinal cord, known collectively as the meninges. The inflammation may be caused by infection with viruses, bacteria, or other microorganisms, and less commonly by certain drugs...
, spreading directly to the brain (primary encephalitis), or may be a complication of a current infectious disease
syphilisSyphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...
(secondary encephalitis). Certain parasitic or
protozoaProtozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
l infestations, such as
toxoplasmosisToxoplasmosis is a parasitic disease caused by the protozoan Toxoplasma gondii. The parasite infects most genera of warm-blooded animals, including humans, but the primary host is the felid family. Animals are infected by eating infected meat, by ingestion of feces of a cat that has itself...
,
malariaMalaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...
, or
primary amoebic meningoencephalitisPrimary amoebic meningoencephalitis is a disease of the central nervous system caused by infection from Naegleria fowleri.-Presentation:...
, can also cause encephalitis in people with compromised
immune systemAn immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
s.
Lyme diseaseLyme disease, or Lyme borreliosis, is an emerging infectious disease caused by at least three species of bacteria belonging to the genus Borrelia. Borrelia burgdorferi sensu stricto is the main cause of Lyme disease in the United States, whereas Borrelia afzelii and Borrelia garinii cause most...
and/or Bartonella henselae may also cause encephalitis.
Another cause is granulomatous amoebic encephalitis.
Diagnosis
Adult patients with encephalitis present with acute onset of fever, headache, confusion, and sometimes seizures. Younger children or infants may present irritability, poor appetite and fever.
Neurological examinations usually reveal a drowsy or confused patient. 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 fluidCerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
obtained by a
lumbar punctureA lumbar puncture is a diagnostic and at times therapeutic procedure that is performed in order to collect a sample of cerebrospinal fluid for biochemical, microbiological, and cytological analysis, or very rarely as a treatment to relieve increased intracranial pressure.-Indications:The...
procedure usually reveals increased amounts of protein and white blood cells with normal glucose, though in a significant percentage of patients, the cerebrospinal fluid may be normal.
CT scanX-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
often is not helpful, as cerebral abscess is uncommon. Cerebral abscess is more common in patients with meningitis than encephalitis. Bleeding is also uncommon except in patients with
herpes simplexHerpes simplex is a viral disease caused by both Herpes simplex virus type 1 and type 2 . Infection with the herpes virus is categorized into one of several distinct disorders based on the site of infection. Oral herpes, the visible symptoms of which are colloquially called cold sores or fever...
type 1 encephalitis.
Magnetic resonance imagingMagnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
offers better resolution. In patients with herpes simplex encephalitis, electroencephalograph may show 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 in the cerebrospinal fluid against a specific viral agent (such as herpes simplex virus) or by
polymerase chain reactionThe polymerase chain reaction is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence....
that amplifies the
RNARibonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
or
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
of the virus responsible (such as
varicella zoster virusVaricella zoster virus is one of eight herpes viruses known to infect humans . It commonly causes chicken-pox in children and Herpes zoster in adults and rarely in children.-Nomenclature:...
).
Treatment
Treatment is usually symptomatic. Reliably tested specific antiviral agents are few in number (e.g. acyclovir for
herpes simplex virusHerpes simplex virus 1 and 2 , also known as Human herpes virus 1 and 2 , are two members of the herpes virus family, Herpesviridae, that infect humans. Both HSV-1 and HSV-2 are ubiquitous and contagious...
) and are used with limited success in treatment of viral infection, with the exception of herpes simplex encephalitis. In patients who are very sick, supportive treatment, such as mechanical ventilation, is equally important. Corticosteroids (e.g.
methylprednisoloneMethylprednisolone is a synthetic glucocorticoid or corticosteroid drug. It is marketed in the USA and Canada under the brand names Medrol and Solu-Medrol. It is also available as a generic drug....
) are used to reduce brain swelling and inflammation. Sedatives may be needed for irritability or restlessness.
Encephalitis lethargica
Encephalitis lethargicaEncephalitis lethargica or von Economo disease is an atypical form of encephalitis. Also known as "sleepy sickness" , it was first described by the neurologist Constantin von Economo in 1917. The disease attacks the brain, leaving some victims in a statue-like condition, speechless and motionless...
is an atypical form of encephalitis which caused an
epidemicIn epidemiology, an epidemic , occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience...
from 1918 to 1930. Those who survived sank into a semi-conscious state that lasted for decades until the Parkinson's drug L-DOPA was used to revive those still alive in the late 1960s by
Oliver SacksOliver Wolf Sacks, CBE , is a British neurologist and psychologist residing in New York City. He is a professor of neurology and psychiatry at Columbia University, where he also holds the position of Columbia Artist...
.
There have been only a small number of isolated cases in the years since, though in recent years a few patients have shown very similar symptoms. The cause is now thought to be either a bacterial agent or an autoimmune response following infection.
Limbic system encephalitis
In a large number of cases, called
limbic encephalitisLimbic encephalitis is a form of encephalitis.In a small number of cases, the pathogens responsible for encephalitis attack primarily the limbic system , often causing memory deficits similar to those observed in Alzheimer's disease or Creutzfeldt-Jakob disease Limbic encephalitis is a form of...
, the pathogens responsible for encephalitis attack primarily the
limbic systemThe limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix, which seemingly support a variety of functions including emotion, behavior, long term memory, and olfaction. The term "limbic" comes from the Latin...
(a collection of structures at the base of the brain responsible for emotions and many other basic functions).
Epidemiology
On Oct 13, 2011 it was reported that in the Indian state of
Uttar PradeshUttar Pradesh abbreviation U.P. , is a state located in the northern part of India. With a population of over 200 million people, it is India's most populous state, as well as the world's most populous sub-national entity...
, 438 people died of Encephalitis.
See also
- Awakenings
Awakenings is a 1990 American drama film based on Oliver Sacks's 1973 memoir Awakenings. It tells the true story of British neurologist Oliver Sacks, fictionalized as American Malcolm Sayer and portrayed by Robin Williams who, in 1969, discovers beneficial effects of the then-new drug L-Dopa...
- Chronic Fatigue Syndrome aka Myalgic Encephalomyelitis
- Rasmussen's encephalitis
Rasmussen's encephalitis, also known as chronic focal encephalitis , is a rare inflammatory neurological disorder, characterized by frequent and severe seizures, loss of motor skills and speech, hemiparesis , encephalitis , and dementia...
External links