Viral encephalitis

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Priyamvada Singh, MBBS [2]; Anthony Gallo, B.S. [3]

Encephalitis is an acute inflammation of the brain, commonly caused by a viral infection. Sometimes, encephalitis can result from a bacterial infection, such as bacterial meningitis, or it may be a complication of other infectious diseases like rabies (viral) or syphilis (bacterial). Certain parasitic or protozoal infestations, such as toxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems. Brain damage occurs as the inflamed brain pushes against the skull, and can lead to death.

It can be classified into primary and secondary post-infectious encephalitis (immune reaction to infection).

It is an acute inflammation of the brain, commonly caused by a viral infection. Sometimes, encephalitis can result from a bacterial infection, such as bacterial meningitis, or it may be a complication of other infectious diseases like rabies (viral) or syphilis(bacterial). Certain parasitic or protozoal infestations, such as toxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems.

Increased risk factors include increased age, weakened immune system, certain geographical locations, outdoor activities and some season of the year (summer and fall).

Its natural history, complications and prognosis depends on age of patient, immune status, type of organism and time to initiate medical therapy. Thus, depending on these factors it may present with complications like seizures, shock, cranial nerve palsy, and coma.

Adult patients with encephalitis may present with acute onset of fever, headache, confusion, weakness and sometimes seizures. Younger children or infants may present with irritability, anorexia and fever. Less commonly, photophobia, stiffness of the neck can occur if meningeal involvement occurs simultaneously with brain involvement. Rarely, patients may present with stiffness of the limbs, slowness in movement and clumsiness, and hallucination depending on which specific part of the brain is involved. The symptoms of encephalitis are caused by the brain’s defense mechanisms activating to get rid of the infection.

It may present as focal or diffuse neurological manifestations. The signs may include altered mental status, change in personality, meningismus, ataxia, seizures, and cranial nerve involvement. Stiff neck, due to the irritation of the meninges covering the brain, indicates that the patient has either meningitis or meningeoncephalitis.

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. Other lab tests that might be useful are complete blood count with differential, coagulation profile, serum electrolyte, urine electrolyte, serum glucose, blood urea nitrogen and serum creatinine levels (to rule out confusion due to dehydration), liver function test (to rule out hepatic involvement), lumbar puncture and CSF examination.

CT scan should be performed in all patient with suspected encephalitis. It helps in excluding ass lesion, bleeding and infarction that could be the possible cause for the encephalopathic state. It should always be performed before lumber puncture in case manifestations suggestive of increased intra-cranial pressure is there.

EEG and brain biopsy are other tests that can be done in patients with encephalitis. In patients with herpes simplex encephalitis, electroencephalograph may show sharp waves in one or both of the temporal lobes.

Treatment with acyclovir with or without steroids and antibiotics should be initiated as soon as possible. Antiviral agent like acyclovir has been useful in treatment of encephalitis due to herpes simplex virus and varicella zoster. Treatment for other causative agents of encephalitis is mostly supportive.

Template:WikiDoc Sources

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Anthony Gallo, B.S. [2]

Encephalitis was first discovered by Sir John Burton Cleland, an Australian microbiologist and professor of pathology, in 1916. Between 1916-1969, Cleland determined encephalitis could result from bacterial infection, viral infection, and autoimmune sequelae.^[1]

Encephalitis was first discovered by Sir John Burton Cleland, an Australian microbiologist and professor of pathology, in 1916. Between 1916-1969, Cleland determined encephalitis could result from bacterial infection, viral infection, and autoimmune sequelae.^[1] There have been several outbreaks of encephalitis, which include:^[2][3]

• 1915-1926: Encephalitis lethargica globally
• 1930s: Japanese encephalitis in Japan, Korea, and Australia
• 1960s: St. Louis encephalitis in the United States

Template:WikiDoc Sources

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Priyamvada Singh, MBBS [2]; Anthony Gallo, B.S. [3]

Encephalitis may be classified into primary and secondary post infectious encephalitis.^[1]

Encephalitis may be classified into primary and secondary post infectious encephalitis. Primary encephalitis occurs when a virus or other infectious agent directly infects the brain. Secondary post infectious encephalitis is an auto-immune reaction of immune system in response to an infection elsewhere in the body, often and often occurs two to three weeks after the initial infection.^[1]

Template:WikiDoc Sources

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Anthony Gallo, B.S. [2]

Encephalitis is an acute inflammation of the brain. Encephalitis is caused by a viral or bacterial infection, with viral being more common. Parasitic or protozoal infestations, such as toxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems. Brain damage occurs as the inflamed brain pushes against the skull, and can lead to subsequent mortality.

Encephalitis is most often caused by a viral infection, which causes inflammation of brain tissue. The brain tissue swells (cerebral edema), which may destroy nerve cells, cause intracerebral hemorrhage, and brain damage. Viruses are usually transmitted via the following routes to the human host:^[1]

• Inhaling respiratory droplets from an infected person
• Contaminated food or drink
• Mosquito, tick, and other insect bites
• Skin contact with an infected person

Following transmission/ingestion, an arbovirus uses the bite site to invade the dendritic cells. The virus replicates within dendrites and macrophages in lymph nodes, resulting in spread to the central nervous system. The exact pathogenesis of encephalitis is not fully understood. It is thought that encephalitis is the result of either:^[1]

• Penetration of cerebrovasculature following endothelial cell infection
• Diapedesis of infected leukocytes
• Penetration of choroid plexus

On microscopic histopathological analysis, the peripheral cuffing of lymphocytes surrounding blood vessels within the brain is the characteristic finding of encephalitis. The following video demonstrates an example of encephalitis:^[2] {{#ev:youtube|uOgS4Vk5qBY}}

Encephalitis lethargica is an atypical form of encephalitis which caused an epidemic from 1917 to 1928.^[3] 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 either a bacterial agent or an autoimmune response following infection.^[4]

In a small number of cases, called limbic encephalitis, the pathogens responsible for encephalitis attack primarily the limbic system (a collection of structures at the base of the brain responsible for basic autonomic functions).

Template:WikiDoc Sources

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ogheneochuko Ajari, MB.BS, MS [2]; Priyamvada Singh, MBBS [3]; Anthony Gallo, B.S. [4]

Life-threatening causes of encephalitis include Balamuthia mandrillaris and Dengue fever. Common causes of encephalitis include infections with viruses such as arboviruss, herpes simplex, measles, mumps, polio, and rabies, which often lead to an autoimmune response. Less common causes of encephalitis include chronic autoimmune disorders and infections with bacteria, fungi, and parasites.

Life-threatening causes include:^[1]

• Balamuthia mandrillaris
• Dengue fever

If left untreated, these conditions may result in subsequent mortality or permanent disability within 24 hours.

• Arbovirus
• Herpes simplex virus
• Measles
• Mumps
• Polio
• Rabies

• 
  This image reveals some of the cytoarchitectural features seen in a lymph node specimen that had been extracted from a patient suspected of a Hantavirus illness. From Public Health Image Library (PHIL). ^[6]

Template:WikiDoc Sources

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Priyamvada Singh, MBBS [2]; Anthony Gallo, B.S. [3]

Encephalitis must be differentiated from other neurologic diseases such as brain abscess, meningitis, status epilepticus, and subarachnoid hemorrhage.

(By organ system)

Template:WikiDoc Sources

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Anthony Gallo, B.S. [2]

The incidence/prevalence of [disease name] is approximately [number range] per 100,000 individuals worldwide.

The incidence of viral encephalitis is approximately 3.5-7.4 per 100,000 individuals in the United States.^[1]

Patients of all age groups may develop encephalitis. Incidence is higher in pediatric populations.^[1]

Males are more commonly affected with encephalitis than females, though both genders are susceptible to the disease.^[1]

There is no racial predilection to the development of encephalitis.^[1] However, Native Americans are predisposed to the development of Rocky Mountain spotted fever, which increases the risk of developing encephalitis.^[2]

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Priyamvada Singh, MBBS [2]; Anthony Gallo, B.S. [3]

Common risk factors in the development of encephalitis are immunodeficiency and extremes of age.

• Age – In general, young children and older adults are at greater risk of most types of viral encephalitis
• Weakened Immune system
• Certain geographical locations are more prone for ticks and mosquitoes bite
• Outdoor activities – It can increase the risk of insects bites
• Season of the year – it is commoner in summer and fall

Template:WikiDoc Sources

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Priyamvada Singh, MBBS [2]; Anthony Gallo, B.S. [3]

Encephalitis is an acute inflammation of the brain, commonly caused by a viral infection. Its natural history, complications and prognosis depends on age of patient, immune status, type of organism and time to initiate medical therapy. Thus, depending on these factors it may present with complications like seizures, shock, cranial nerve palsy, and coma.

• Increase intracranial pressure
• Cranial nerve palsy
• Shock
• Coma
• Seizures
• Syndrome of inappropriate secretion of antidiuretic hormone (SIADH)
• Permanent brain damage may occur in severe cases of encephalitis and can affect, Hearing, Memory, Muscle control, Sensation, Speech , and Vision

The outcome varies. Some cases are mild and short, and the person fully recovers. Other cases are severe, and permanent impairment or death is possible. The acute phase normally lasts for 1 – 2 weeks. Fever and symptoms gradually or suddenly disappear. Some people may take several months to fully recover.

Template:WikiDoc Sources