"Encephalitis" describes conditions in which the brain becomes irritated and inflamed. As the Mayo Clinic explains, one of the more common causes of encephalitis is an infection from a virus. These viruses can directly damage the brain, but the immune response they generate can also be dangerous. Viral encephalitis can be difficult to treat because viruses cannot be treated with antibiotics.
Types
As the National Institute of Neurological Diseases and Stroke (NINDS) explains, there are two types of viral encephalitis. Primary viral encephalitis is caused by a virus directly infecting the brain. Secondary viral encephalitis is caused by a virus infecting other tissues in the body and then eventually traveling to the brain.
Viruses
The Mayo Clinic explains that there are several different viruses that account for the majority of cases of primary encephalitis. The herpes simplex virus (especially the HSV 1 strain) is the most common cause of viral encephalitis. Arboviruses, a class of viruses transmitted by mosquitoes and other insects and include the West Nile virus, can also lead to encephalitis. Rabies, varicella-zoster (the virus that causes chickenpox and shingles) and the Epstein-Barr virus can also cause viral encephalitis.
Pathophysiology
The Merck Manual explains that viral encephalitis can damage neurons via a couple of different mechanisms. The viral infection itself can damage the neurons. The infection can cause cells to develop small bits of cellular tissue--called "inclusion bodies"--which are characteristic of viral damage. Viral infection of the neurons also can lead to inflammation, which can lead to swelling around the brain and small hemorrhages to develop, which can also cause permanent brain damage.
Symptoms and Diagnosis
The most common symptoms of viral encephalitis include a severe headache, a fever and alterations in the patient's mental status. The Merck Manual explains that patients often will develop seizures. Olfactory seizures (which are manifested by the patient detecting foul odors, such as rotten eggs, that are not actually present) are indicative of herpes encephalitis. Viral encephalitis is usually diagnosed using an MRI of the brain as well as a testing of the patient's cerebrospinal fluid.
Treatment
Many cases of viral encephalitis, according to the Mayo Clinic, are difficult to treat because some viruses are resistant to antiviral medications. Susceptible viruses can be treated with antiviral medications (such as acyclovir). Otherwise, most patients are given supportive care (which includes electrolytes and fluids) and are told to rest. Severe cases of viral encephalitis can be treated with corticosteroids (to reduce inflammation) and anti-convulsants (to prevent seizures).
