Encephalitis; Causes, Symptoms, Diagnosis, Treatment

Encephalitis
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Encephalitis is an inflammation of the brain. Encephalitis is an acute inflammation swelling of the brain usually resulting from either a viral infection or due to the body’s own immune system mistakenly attacking brain tissue. Symptoms may include a headache, fever, confusion, a stiff neck, and vomiting. Complications may include seizures, hallucinations, trouble speaking, memory problems, and problems with hearing.

Types of Encephalitis

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 majority of viral cases of encephalitis have an unknown cause, however the most common identifiable cause of viral encephalitis is from herpes simplexinfection. Other causes of acute viral encephalitis are rabies virus, poliovirus, and measles virus.

Additional possible viral causes are arbovirus (St. Louis encephalitis, West Nile encephalitis virus), bunyavirus (La Crosse strain), arenavirus(lymphocytic choriomeningitis virus) and reovirus (Colorado tick virus). The Powassan virus is a rare cause of encephalitis.

Bacterial and other

It can be caused by a bacterial infection, such as bacterial meningitis, or may be a complication of a current infectious disease syphilis(secondary encephalitis).

Certain parasitic or protozoal infestations, such as toxoplasmosis, malaria, or primary amoebic meningoencephalitis, can also cause encephalitis in people with compromised immune systems. Lyme disease or Bartonella henselae may also cause encephalitis. Other bacterial pathogens, like Mycoplasma and those causing rickettsial disease, cause inflammation of the meninges and consequently encephalitis. A non-infectious cause includes acute disseminated encephalitis which is demyelinated.

Limbic encephalitis

Limbic encephalitis refers to inflammatory disease confined to the limbic system of the brain. The clinical presentation often includes disorientation, disinhibition, memory loss, seizures, and behavioral anomalies. MRI imaging reveals T2 hyperintensity in the structures of the medial temporal lobes, and in some cases, other limbic structures. Some cases of limbic encephalitis are of autoimmune origin.

Autoimmune encephalitis

Autoimmune encephalitis signs can include catatonia, psychosis, abnormal movements, and autonomic dysregulation. Antibody-mediated anti-N-methyl-D-aspartate-receptor encephalitis and Rasmussen encephalitis are examples of autoimmune encephalitis. Anti-N-methyl-D-aspartate-receptor encephalitis is the most common autoimmune form, and is accompanied by ovarian teratoma in 58 percent of affected women 18-45 years of age.

Encephalitis lethargica

Encephalitis lethargica is identified by high fever, headache, delayed physical response, and lethargy. Individuals can exhibit upper body weakness, muscular pains, and tremors, though the cause of encephalitis lethargica is not currently known. From 1917 to 1928, an epidemic of encephalitis lethargica occurred worldwide.

Causes of Encephalitis

There are two main types of encephalitis

Primary encephalitis

This condition occurs when a virus or other agent directly infects the brain. The infection may be concentrated in one area or widespread. A primary infection may be a reactivation of a virus that had been inactive after a previous illness.

  1. Common viruses, including HSV (herpes simplex virus) and EBV (Epstein-Barr virus)
  2. Childhood viruses, including measles and mumps
  3. Arboviruses (spread by mosquitoes, ticks, and other insects), including Japanese encephalitis, West Nile encephalitis, and tick-borne encephalitis
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Secondary encephalitis

This condition results from a faulty immune system reaction to an infection elsewhere in the body. Instead of attacking only the cells causing the infection, the immune system also mistakenly attacks healthy cells in the brain. Also known as post-infection encephalitis, secondary encephalitis often occurs two to three weeks after the initial infection.

The viruses that can cause encephalitis include

  • Herpes simplex virus (HSV) – Both HSV type 1 — associated with cold sores and fever blisters around your mouth — and HSV type 2 — associated with genital herpes — can cause encephalitis. Encephalitis caused by HSV type 1 is rare but can result in significant brain damage or death.
  • Other herpes viruses – These include the Epstein-Barr virus, which commonly causes infectious mononucleosis, and the varicella-zoster virus, which commonly causes chickenpox and shingles.
  • Enteroviruses – These viruses include the poliovirus and the coxsackievirus, which usually cause an illness with flu-like symptoms, eye inflammation and abdominal pain.
  • Mosquito-borne viruses – These viruses can cause infections such as West Nile, La Crosse, St. Louis, western equine and eastern equine encephalitis. Symptoms of an infection might appear within a few days to a couple of weeks after exposure to a mosquito-borne virus.
  • Tick-borne viruses – The Powassan virus is carried by ticks and causes encephalitis in the Midwestern United States. Symptoms usually appear about a week after a bite from an infected tick.
  • Rabies virus – Infection with the rabies virus, which is usually transmitted by a bite from an infected animal, causes a rapid progression to encephalitis once symptoms begin. Rabies is a rare cause of encephalitis in the United States.
  • Childhood infections – Common childhood infections — such as measles (rubeola), mumps and German measles (rubella) — used to be fairly common causes of secondary encephalitis. These causes are now rare in the United States due to the availability of vaccinations for these diseases.

The following is a short summary of the viruses that cause the majority of encephalitis infections, although they may also cause other diseases.

DiseaseGeographic LocationVector/ HostsComment
Herpes encephalitisUnited States/the worldHuman-to-human
contact
Prompt treatment with acyclovir increases survival to 90%
West Nile encephalitisAfrica, West Asia, Middle East, United StatesMosquito/mostly birdsMajority are mild cases. Less than 1% of those infected will become severely ill. Full recovery is expected. A vaccine for humans is not commercially available.
Eastern equine
encephalitis
East Coast (from
Massachusetts to Florida),
Gulf Coast
Mosquito/birdsOften occurs in horses. High mortality rate (50%-75%); frequent outcomes (seizures, slight paralysis), especially in children
Western equine
encephalitis
Western United States and
Canada
Mosquito/birdsOften occurs in horses.
Particularly affects infants
Venezuelan equine
encephalitis
Western HemisphereMosquito/rodentsRare in United States; low mortality rate, rare after-effects
La Crosse encephalitisThroughout the United States, especially in midwestern & southeastern regionsMosquito/ chipmunks,
squirrels
Most common cause of
encephalitis in children younger than 16 years of age
St. Louis encephalitisMidwestern & mid-Atlantic
United States
Mosquito/birdsMostly affects adults
Japanese encephalitisTemperate Asia, southern and southeastern AsiaMosquito/birds and pigsVaccine available for ages 17 and older. See
Prevention section.
High morbidity/mortality rates
Zika virusSouth America, Asia, Pacific Islands, Central AmericaMosquitoesBirth defects including microcephaly, neurologic damage

Symptoms of Encephalitis

Most people with viral encephalitis have mild flu-like symptoms, such as

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Diagnosis of Encephalitis

Diagnosing encephalitis is done via a variety of tests

Brain scan, can determine inflammation and differentiate from other possible causes.

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Treatment of Encephalitis

Treatment (which is based on supportive care) is as follows

Pyrimethamine-based maintenance therapy is often used to treat Toxoplasmic Encephalitis (TE), which is caused by Toxoplasma gondii and can be life-threatening for people with weak immune systems. The use of highly active antiretroviral therapy ,

Prevention of Encephalitis

Make sure that you and your children get shots (vaccines) against measles, mumps, rubella, chickenpox, and the flu.

Avoid areas where there has been an outbreak of viral encephalitis. If you can’t avoid these areas, prevent mosquito bites with these tips:

  • Stay indoors at dawn, at dusk, and in the early evening, when mosquitoes are most active.
  • Wear long-sleeved shirts and long pants whenever you are outdoors and are likely to be where mosquitoes are.
  • Avoid wearing floral fragrances from perfumes, soaps, hair care products, and lotions. These may attract mosquitoes.
  • Use insect repellent with DEET (N,N-diethyl-meta-toluamide). The repellent is available in varying strengths up to 100%. The American Academy of Pediatrics (AAP) and other experts suggest that it is safe to use a repellent that contains 10% to 30% DEET on children older than age 2 months.
  • Spray clothing with an insect repellent containing permethrin or DEET, because mosquitoes may bite through thin clothing. DEET can damage plastic items, such as watch crystals or eyeglass frames, and some synthetic fabrics. You also can use natural products such as soybean-based Bite Blocker.
  • Avoid applying repellent to the hands of children. Repellents may irritate the eyes and mouth.
  • Whenever you use an insecticide or insect repellent, be sure to read and follow the directions for use.
  • Do not keep open containers of water near your house. Standing water is a breeding place for mosquitoes.
  • If you are taking a long trip to the Far East or to central or eastern Europe, talk to your doctor about getting vaccinated against certain types of mosquito- or tick-borne encephalitis. For example, there is a vaccine for Japanese encephalitis. Getting vaccinated is especially important if you are going to a rural area.

References

Encephalitis

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