What is Viral Encephalitis?
Viral encephalitis is an inflammation, or swelling, in the brain caused by a virus. This is the most common form of encephalitis and often occurs alongside viral meningitis, which is an infection of the membranes covering the brain and spinal cord. The virus first invades a host outside the central nervous system, which includes the brain and spinal cord, and then reaches the spinal cord and brain either through the bloodstream or by moving backwards from nerve endings.
The disease tends to affect younger people more often than the elderly. However, environmental factors also play a key role. Many instances of viral encephalitis go unnoticed due to the lack of tests and mild symptoms. Moreover, research indicates that many patients produce a high amount of antibodies, which are proteins that the body produces to fight off viruses, but don’t show any symptoms.
What Causes Viral Encephalitis?
Infectious encephalitis, which is a brain inflammation, can be caused by a range of sources including bacteria, viruses, fungi, and parasites. Despite thorough examinations, the root cause of many encephalitis cases remains unknown. Viruses are the most common known cause, making up about 70% of confirmed encephalitis cases.
In the United States, the viruses that most commonly cause encephalitis are the herpes simplex virus (HSV), West Nile virus, and enteroviruses. Other viruses that can cause encephalitis include the chickenpox virus (varicella-zoster), Epstein-Barr virus which causes mononucleosis, cytomegalovirus, human herpesviruses 6 and 7, measles, mumps, rubella, the St. Louis virus, eastern and western equine viruses, dengue, and rabies.
Risk Factors and Frequency for Viral Encephalitis
Viral encephalitis impacts between 3.5 and 7.5 individuals per 100,000, with the highest rates seen in the very young and elderly. Its causes have evolved over time. For example, thanks to vaccines, cases of mumps and measles causing encephalitis have decreased. However, EBV and CMV encephalitis occurrences have increased because these are common in people with weakened immune systems, like those with AIDS, or those undergoing transplants or chemotherapy.
Different factors can affect the occurrence of encephalitis, including the time of year, where you live, and any exposure to animals or insects. Some viruses, like those causing St. Louis encephalitis and tick-borne encephalitis show up in certain locations and during particular times of the year, such as summer when mosquitoes are active.
- The disease is spread to the brain through the bloodstream.
- In the United States, the most common cause of encephalitis is the herpes simplex virus.
- People who work in warm, humid environments where mosquitoes thrive are especially at risk for certain types of viral encephalitis.
Signs and Symptoms of Viral Encephalitis
Even after extensive tests, in many cases, the cause of encephalitis, an inflammation of the brain, remains elusive. Therefore, the patient’s history and physical examination become crucial for diagnosing this condition. Various factors such as immunity, contact with insects or animals, travel history, vaccination record, geographical location, and time of year play a significant role. The typical symptoms include fever, headache, seizures, and changes in mental state. Behavioral changes, hallucinations, and cognitive declination are also commonly observed neuropsychiatric features. Some patients might also display symptoms or signs specific to the virus causing their condition. For example:
- Rash and skin blisters are indicators of herpes zoster encephalitis
- Enlarged lymph nodes and spleen are usually associated with EBV
- HSV encephalitis, which mainly affects the temporal and frontal lobes, often leads to psychiatric symptoms, memory loss, and speech difficulties
- Infections with some arboviruses can cause involuntary movements and symptoms related to Parkinson’s disease due to their impact on basal ganglia, a brain region.
Additionally, specific viruses can lead to certain characteristic signs:
- JE often results in symptoms mimicking Parkinson’s disease
- Enterovirus 71 may lead to shaking, muscle twitching, lack of coordination, fluid accumulation in the lungs and paralysis of cranial nerves
- Nipah virus can cause signs related to brainstem and cerebellum, hypertension, and muscle twitching restricted to a specific body region
- Zika virus infection typically leads to microcephaly, a condition characterized by a smaller than average head size
Testing for Viral Encephalitis
If you are being checked for viral encephalitis, which is inflammation of the brain, the first tests your doctor will usually do involve imaging of your brain and a procedure called a lumbar puncture. Brain imaging such as Computed Tomography (CT) scans or Magnetic Resonance Imaging (MRI) will help to rule out any increase in the pressure inside your skull and any potential for certain types of herniations in the brain before the lumbar puncture is performed.
CT scans can sometimes show signs of damage, or lesions, in the temporal lobes of your brain when the herpes simplex virus (HSV) is causing the encephalitis. These lesions usually show up 3 to 5 days after the start of the infection.
MRI scans are the most sensitive for showing consistent findings with HSV encephalitis, such as damage in the temporal and frontal lobes of the brain. Lumbar puncture, also known as a spinal tap, involves taking a sample of your cerebrospinal fluid (CSF) which surrounds the brain and spinal cord. This fluid is checked for its pressure, cell count, sugar levels, and protein content.
This fluid can also be tested specifically for certain viruses like herpes simplex 1 and 2 and enteroviruses. Other tests based on your history and symptoms, such as checking for mosquito-borne or HIV viruses, may also be done. If no cause can be found from these tests, a brain biopsy (taking a small sample of brain tissue) or culturing and PCR testing of other body fluids may be necessary in some cases.
When the CSF is tested, you will usually see normal sugar levels, moderately high protein levels, and an increase in a type of white blood cell called lymphocytes. However, in about 10% of patients, their CSF test results will be normal.
An electroencephalogram (EEG), a test that records the electrical signals in your brain, might show abnormal patterns if you are having seizures. Japanese encephalitis, for example, often shows up with three EEG patterns which include diffuse slow wave activity with spikes, continuous slow wave activity, and alpha comma activity.
Treatment Options for Viral Encephalitis
The treatment for viral encephalitis, an infection that causes inflammation of the brain, is typically focused on relieving symptoms because there isn’t an established treatment for most viral infections of the brain. However, there’s an important exception for Herpes Simplex Virus (HSV) encephalitis. Early use of a drug called acyclovir can significantly reduce the risk of death and severe long-term complications like behavioural and mental problems. For this reason, it’s generally recommended that doctors start all patients suspected of having encephalitis on acyclovir, just to be safe. This drug is also used for other types of herpesviruses. For varicella-zoster virus, a virus that can cause chickenpox and shingles, acyclovir along with corticosteroids, which helps reduce inflammation, is advised for patients with healthy immune systems. Meanwhile, the recommended treatment for cytomegalovirus (CMV) encephalitis, another type of herpesvirus, is a combination of two drugs, ganciclovir and foscarnet, taken over three weeks.
It’s also important to regularly monitor the amount of pressure inside a patient’s skull (known as intracranial pressure or ICP), since high levels can lead to a poorer prognosis. Although there’s not much evidence on their effectiveness specifically for viral encephalitis, doctors sometimes use steroids and mannitol, a type of drug that decreases brain swelling, to relieve increased ICP.
In cases where the patient has seizures, medications such as valproic acid or phenytoin may be given. If the seizures are severe and ongoing (a condition called status epilepticus), benzodiazepines, a type of tranquilizer, may be necessary. Lastly, for patients who show changes in behaviour, short-term use of antipsychotic drugs could be needed.
What else can Viral Encephalitis be?
When diagnosing encephalitis – an inflammation of the brain, doctors have to consider many different possible causes. These could be either infections or non-infections. The range of potential causes includes:
- Cancer
- Diseases linked to the body’s immune response or associated with cancer (like anti-NMDA receptor encephalitis)
- Abscess in the brain
- Tuberculosis
- Confusion caused by medication use
- Neurosyphilis – a neurological complication of syphilis
- Bacterial, fungal, protozoal, or helminthic encephalitis – which are different types of infections in the brain
It’s essential that all these are considered when trying to arrive at the correct diagnosis.
What to expect with Viral Encephalitis
Most people who get viral encephalitis, which is an inflammation of the brain caused by a virus, get better without any long-term effects. However, some might continue to experience problems like focusing issues, changes in speech or behavior, and memory loss. In rare situations, some patients might end up in a vegetative state, which means they’re awake but showing no signs of awareness.
In children, some forms of this infection, such as the Western Equine Encephalitis (WEE), may lead to seizures and changes in behavior. Another form, called Eastern Equine Encephalitis (EEE), can result in seizures, severe mental disabilities, and different types of paralysis. Pregnancy infection with the Zika virus might lead to microcephaly, which is a condition where a baby’s head is significantly smaller than expected, often due to abnormal brain development.
One of the most common long-term complications after viral encephalitis is the development of seizures in 10-20% of patients, which may take place over several decades. These seizures are often hard to control with medication. However, seizures that affect only one part of the inner region of the brain, known as unilateral mesial temporal lobe seizures, can be effectively treated with brain surgery.
Possible Complications When Diagnosed with Viral Encephalitis
After a patient experiences encephalitis, they may undergo various changes and face a number of health issues, such as:
- A decline in intellectual capabilities
- Alterations in their mood and behavior
- Remaining neurological deficits or impairments
- Extra conditions related to brain disorders
- Low sodium level in the blood
- Severe brain dysfunction
- Dysfunction of a single nerve
- Weakness or loss of muscle tone
- Condition characterized by high levels of a hormone causing water and salt imbalance
