Introduction
Encephalitis is the inflammation of brain tissue. The isolated infection of the brain, without involvement of the meninges, is most often caused by viruses. The course is usually mild.
However, the disease can also have severe to fatal consequences. More common is the inflammation of the meninges, which is called meningitis. In the case of such infections, the brain tissue can also be affected if no or insufficient treatment is given – meningoencephalitis develops. If the cause of the disease is viral, the spinal cord may be involved, which is known as encephalomyelitis.
Causes
Viruses are the main cause of encephalitis without involvement of the meninges. Often, however, the inflammation also results from a previous bacterial attack of the meninges (meningitis), which spreads to the brain cells (neurons). This is called meningoencephalitis.
If fungi or other parasites are the cause of encephalitis, it is rare in people with a healthy immune system, but in immunocompromised patients it is often the result of a longstanding illness, such as HIV infection. Viral pathogens: Viruses reach the brain via the bloodstream or retrogradely (migrating backwards) via nerve tracts that lead to brain tissue either directly or indirectly via the spinal cord. They can be transmitted through direct physical contact, but droplet infection or sexual intercourse.
Most encephalitides are caused by Herpes simplex virus I, which has already been present in the body before and eventually breaks out. More than 90% of the population carries the virus in itself, sometimes without even knowing about it. Usually, the initial infection with the so-called herpes labiales (lip herpes) occurs in childhood, which has no significant consequences and does not require any special treatment.
The pathogen then attaches itself to the host’s so-called nerve nodes (spinal ganglia) and remains there until the end of the host’s life. If the immune system is weakened, the virus may reappear and cause herpes simplex encephalitis. Other relevant virus strains: involvement of the meninges is the rule in the Epstein-Barr virus, in the pathogen causing early summer meningo-encephalitis (flavovirus) and in HIV infection.
Bacterial pathogens: Bacterially caused encephalitis is usually the result of a previous meningitis, an inflammation of the meninges that has not been sufficiently treated or for which therapy has not been effective. A special role in the bacterial genesis (cause) of encephalitis is played by spirochetes, a bacterial genus that presents itself under the microscope as spiral-shaped pathogens. Treponema pallidum causes neurosyphilis and Borellia burgdorferii causes neuroborreliosis.
Furthermore an infection with Rickettsia prowazekii can cause typhus encephalitis. Other pathogens: Rarer than viruses or bacteria, other pathogens cause encephalitis. The immune status, i.e. the health condition of the patient, is very important here.
Because the worse it is, the more likely it is that the patient will be infected with various rare pathogens, such as protozoa (unicellular organisms, most commonly Toxoplasma gondii), helminths (worms, most commonly schistosomes) and fungi (most commonly Aspergillus fumigatus and Cryptococcus neoformans).
- Varicella zoster virus (chickenpox, shingles)
- Cytomegalovirus
- Measles virus (Measles)
- Rubella virus (German measles)
- Influenza virus (flu)
- HIV
- Rabies virus (rabies)
Viral encephalitis is a viral infection of the brain, which can be acute or chronic. Especially children, elderly people and people with a weakened immune system have an increased risk of developing viral encephalitis.
The disease is caused by entero-, herpes- and adenoviruses or TBE (early summer meningo-encephalitis) and mostly occurs in the warm seasons. The viruses attack the central nervous system (CNS), cross the blood-brain barrier and cause inflammation in the brain. To control the infection, the body reacts with an immune response, which as collateral damage leads to lesions in the CNS.
The symptoms of viral encephalitis are very diverse and depend on which brain region is affected by the inflammation. Initially, the symptoms resemble those of influenza and include headache, fever, fatigue, nausea with vomiting and sensitivity to light. Later, seizures and disturbances of consciousness (vigilance disorders) occur.
Patients also suffer from neck stiffness (meningismus) with simultaneous inflammation of the meninges.Paralysis and psychotic changes are also possible with encephalitis. The diagnosis is made by means of a lumbar puncture with pathogen detection in the spinal fluid and imaging procedures such as CT or MRI. The disease is only treated symptomatically and antiviral drugs are only used for herpes virus and HIV infection.
With immediate treatment, the chances of cure are good. Herpes encephalitis is an inflammation of the brain caused by herpes simplex viruses (HSV). Mostly it is an infection with the herpes simplex virus type 1.
Worldwide there is a high infestation with HSV, whereby the infections often remain asymptomatic or manifest themselves as herpes labialis. The viruses can spread to the brain via the olfactory nerve and lead to encephalitis. Stress and a weakened immune system favour the infection.
The encephalitis leads to fever and meningismus, seizures, psychotic symptoms and increasing disturbances of consciousness up to coma. If herpes encephalitis is suspected, the intravenous administration of antivirals (drugs that stop the viruses from multiplying) must be carried out immediately, otherwise the disease has a high mortality rate of 70%. There is a high risk of secondary damage such as paralysis and mental impairment.
Tick-borne encephalitis is also called early summer meningoencephalitis (TBE). This viral disease is transmitted from ticks to humans and leads to a combined inflammation of the brain and meninges. Southern Germany, Austria and the Czech Republic in particular are considered endemic areas where a large proportion of ticks carry the TBE virus in their blood and where the risk of infection is particularly high.
A tick bite carries the viruses into humans and, above all, people who are frequently in the forest, such as forestry workers, hunters or farmers, are at a high risk of contracting TBEE. After an incubation period of 7 to 14 days, the first symptoms of tick-borne encephalitis become noticeable, resulting in fever, headache and aching limbs. After a few days, the symptoms subside and a symptom-free phase follows.
As the disease progresses, the viruses attack the central nervous system and neurological symptoms develop: Headaches, nausea, vomiting, neck stiffness, loss of consciousness and possibly paralysis or cramps. Encephalitis caused by ticks has a favorable prognosis and in most cases the disease heals completely. In some cases, however, late effects remain.
Once the disease is over, the affected persons have a lifelong immunity to tick-borne encephalitis. Persons who stay longer in risk areas should consider a TBE vaccination. Influenza viruses (influenza viruses) can lead to influenza encephalitis or influenza encephalitis.
This is a rare but serious complication of influenza in which the viruses enter the brain and cause an inflammation. Symptoms of influenza encephalitis include high fever, headache and neck stiffness. It can also cause severe neurological symptoms such as clouding of consciousness and seizures.
Children are particularly affected by influenza encephalitis because their nervous system is particularly sensitive to harmful influences. In the first days of an influenza illness with influenza A or influenza B, the viruses can spread to the brain and lead to encephalitis. However, disease outbreaks have also been observed in the later stages of influenza.
A flu vaccination can prevent serious infections with influenza and thus influenza encephalitis. Therefore, especially children and young adults should receive a flu vaccination. Influenza encephalitis is a serious illness with a complicated course, especially for children.
If influenza encephalitis is suspected, a lumbar puncture and an MRI examination are performed and, if the diagnosis is confirmed, therapy is started immediately. Patients receive antiviral medication and in many cases must be monitored in the intensive care unit. Japanese Encephalitis is a tropical disease that causes inflammation of the brain in various Southeast Asian countries.
The inflammation is triggered by the Japanese Encephalitis Virus (JEV), which infects pigs and wild birds. Mosquitoes ingest the pathogen through a blood meal on infected animals and transmit the virus to humans through a bite. In humid areas where there are many mosquitoes and during the monsoon season, there is a high risk of infection and every few years there are epidemic outbreaks of the disease in Asia.Meanwhile, there is an effective vaccine and vaccination is recommended for longer stays in risk areas.
The symptoms of Japanese Encephalitis appear 5 to 15 days after infection by the mosquito bite and resemble the general characteristics of encephalitis. These include headache, high fever, stiff neck and neurological deficits. Rapid hospital treatment is important to minimize the risk of late complications and disability. Untreated, Japanese Encephalitis often leads to death.
