Synonyms in a broader sense
encephalitis, meningitis, herpes
Definition
The encephalitis caused by the Herpes Simplex Virus Type 1 (HSV1) is the most common form of acute viral encephalitis (inflammation of the brain) with about one new case per 100,000 inhabitants per year (5 per 100,000 in Western Europe). If it is detected and treated early, the prognosis is good. However, if left untreated, 70% of patients die, which is the reason why treatment MUST be given on suspicion alone, i.e. without having identified the pathogen. The herpes simplex virus is also the causative agent of the harmless cold sore.
Disease and symptoms
The herpes virus enters the central nervous system via the olfactory nerves and from there enters the lateral (temporal) and frontal (frontal) lobes of the brain, first only on one side (usually the left), later usually on both sides. This is where the areas of the brain are located that are important for our language, our memory and our psyche, especially the limbic system. This is where bleeding and tissue destruction (necrotizing hemorrhagic encephalitis) occur, followed by extensive swelling around this area of the brain (cerebral edema), which can be easily detected by MRI (magnetic resonance imaging) and which leads to the characteristic neurological and neuropsychological focal point symptoms: Many patients can no longer speak, they have a so-called aphasia.
Mild hemiplegia can also develop. In 60 % of the cases an epileptic seizure occurs (focal seizures, focus = focus). Neck stiffness and clouding of consciousness are added.
If left untreated, this can increase to a coma. Intracranial pressure develops, from which the patient may ultimately die. Herpes simplex viruses (type 1) are transmitted via secretion droplets that originate from the human respiratory tract (droplet infection).
Infection can occur through direct contact with the mucous membranes in the mouth and throat or through the absorption of the secretion droplets via the air. In adulthood, however, about 95% of people are already infected with herpes simplex viruses (type 1). A renewed infection does not represent an increased risk of herpes encephalitis.
The viruses persist for life in the nerve cells and are reactivated, especially when the immune system is weakened. There is a risk that the viruses will migrate along the nerve fibers into the brain and cause encephalitis (inflammation of the brain). Herpes simplex viruses (type 1) are transmitted by droplet infection.
After the secretion droplets have been absorbed via the mucous membranes in the nasopharynx, the pathogens settle there. Inflammation in the surrounding areas leads to a primary infection, which manifests itself mainly in children through fever and painful blisters in the mouth and throat. Subsequently, the viruses are absorbed into the nerve endings running through the mucous membrane.
Along these nerve endings, the viruses can spread to nerve ganglia (accumulation of nerve cell bodies) and persist (remain) there for a lifetime. Due to a weakened immune system, the viruses can migrate again along the nerves and form the typical herpes blisters in the area where the nerves are supplied (often in the area of the lips). In addition, there is a risk of the viruses spreading along the nerves into the brain, which can lead to an inflammation of the brain (encephalitis).