Q 2.11. Encephalomyelitis. Classification, viral encephalomyelitis. Poliomyelitis, rabies, tick-borne encephalitis. Herpes infections.

Encephalomyelitis is a term used to describe inflammation of both the brain and spinal cord (myelitis). This inflammation can be caused by various factors, including infections, autoimmune reactions, or other inflammatory processes. The affection of central nervous system can lead to a range of symptoms depending on the underlying cause and the affected area.


Acute Disseminated Encephalomyelitis (ADEM): This type is typically characterized by widespread inflammation in the brain and spinal cord following a viral infection or vaccination.

Infectious Encephalomyelitis: This form is caused by viral, bacterial, fungal, or parasitic infections that directly affect the brain and spinal cord. 

Post-infectious Encephalomyelitis: After a viral infection has resolved, the immune system continues to attack the nervous system, leading to inflammation and damage.

Symptoms of Encephalomyelitis:

  • headache
  • fever
  • altered mental status
  • confusion
  • memory problems
  •  weakness/ paralysis
  • coordination problems
  • numbness/ tingling 
  • difficulty speaking/ understanding speech
  • seizures
  • double/blurred/ loss of vision
  • mood changes
  • depression/anxiety



Physical Examination

Imaging Studies: MRI scans of the brain and spinal cord to visualize inflammation, lesions, or abnormalities.

Lumbar Puncture: For collecting cerebrospinal fluid (CSF) from the spine and look for signs of inflammation, infection, or other abnormalities.

Blood Tests: for infection, autoimmune markers.



Treatment may involve medications to reduce inflammation, manage symptoms, suppress the immune system (in autoimmune cases), and treat any underlying infections or other conditions contributing to the inflammation. Early diagnosis and treatment are essential for managing encephalomyelitis effectively and minimising potential complications.


Viral encephalomyelitis 

Encephalomyelitis, also known as inflammation of the brain and spinal cord, arises due to the immune system’s reaction to viral infection.

Among humans, the most common causative agents of viral encephalomyelitis are enterovirus (such as polio), rhabdovirus (such as rabies). 

The predominant targets for most encephalitis viruses are neurons, although a subset may attack cerebrovascular endothelial cells, leading to ischemia and stroke, or glial cells, inducing demyelination, encephalopathy, or dementia. 

Since encephalitic virus infections typically originate outside the central nervous system (e.g., via insect bites, skin, respiratory, or gastrointestinal routes), the innate and adaptive immune responses usually act rapidly to prevent virus penetration into the CNS. Consequently, most viruses capable of causing encephalitis more commonly result in either asymptomatic infection or a febrile illness devoid of neurological manifestations, making encephalomyelitis an infrequent complication of infection.


  • stiff neck and back
  • confusion
  • vomiting
  • mood and personality changes
  • headache
  • fever
  • confusion
  • memory loss
  • seizures
  • paralysis



Poliomyelitis, commonly known as polio, is a highly contagious viral illness primarily impacting children below the age of 5. The virus spreads via person-to-person contact, mainly through the fecal-oral route or occasionally through contaminated water or food, and replicates in the intestines. From there, it can infiltrate the nervous system, potentially leading to paralysis. Most individuals infected with the poliovirus, which is responsible for polio, do not display symptoms.

Abortive polio

Approximately 5% of poliovirus-infected individuals experience a mild form of the illness known as abortive poliomyelitis. This manifests as flu-like symptoms lasting 2 to 3 days, including:

  • fever
  • headache
  • muscle pain
  • sore throat
  • stomachache
  • loss of appetite
  • nausea
  • vomiting.

Non paralytic polio

A more severe variant, termed nonparalytic polio, affects around 1% of those infected. Although the illness persists beyond a few days, it does not result in paralysis. In addition to intensified flu-like symptoms, nonparalytic polio may also involve:

  • neck pain/ stiffness
  • arm/ leg pain/ stiffness
  • severe headaches

Following, a second phase of symptoms may emerge, characterized by spinal and neck stiffness, decreased reflexes, and muscle weakness.

Paralytic polio

This rare, most severe form of polio starts similarly to nonparalytic polio but progresses to more intense signs and symptoms. These include severe pain, heightened sensitivity to touch, tingling or pricking sensations, muscle spasms or twitching, and muscle weakness evolving into partial paralysis. While any combination of limbs may become paralyzed, paralysis of one leg is most typical, followed by paralysis of one arm. Depending on the disease’s severity, other symptoms may involve:

  •  paralysis of respiratory muscles
  • difficulty swallowing
  • post-polio syndrome

Post-polio syndrome

Post-polio syndrome may arise decades after initial polio infection, presenting with new or worsening symptoms. Common manifestations include:

  • progressive muscle or joint weakness and pain
  • fatigue
  • muscle wasting
  • breathing/ swallowing difficulties
  • sleep-related breathing disorders (like sleep apnea)



Rabies, a viral infection thats usually caused from a bite or scratch of an infected animal. The virus targets the central nervous system of mammals, leading to brain disease and eventual death. The virus, present in saliva, poses a risk of infection if transmitted through an infected animal’s bite or contact between infected saliva and a wound or mucous membrane, like the eyes or mouth. However, it cannot penetrate intact skin.

In the United States, the primary carriers of rabies are typically bats, coyotes, foxes, raccoons, and skunks. Conversely, in developing nations, it’s stray dogs that pose the highest risk of transmitting rabies to humans.

Once symptoms of rabies become apparent in an individual, the disease almost invariably leads to death. Due to this reason, individuals at risk of rabies exposure should promptly receive rabies vaccinations to safeguard against infection.

Phases of disease


Incubation refers to the period before symptoms manifest, lasting from 2 to 3 months, varying based on the virus’s entry point and quantity. The closer the bite is to the brain, the quicker symptoms may appear. Rabies symptoms typically lead to fatality by the time they manifest. Thus, anyone exposed to the virus should receive immediate medical attention without waiting for symptoms.

Prodrome phase

During the prodrome phase, early flu-like symptoms such as fever, headache, anxiety, sore throat, nausea, and discomfort at the bite site occur. The acute neurologic period follows:

  • confusion
  • aggression
  • muscle twitching and rigidity
  • seizures
  • difficulty breathing
  • hypersalivation
  • fear of water
  • hallucinations
  • insomnia


Coma often ensues, with death occurring within three days, even with supportive care.


Furious rabies

Characterized by hyperactivity, hallucinations, hydrophobia, and sometimes aerophobia, leading to death from cardiorespiratory arrest.

Paralytic rabies

Known for paralysis and coma, occurring in 20% of human cases, with symptoms beginning at the bite or scratch site and progressing to coma and death.

The patient is usually asymptomatic  for 1 to 3 months before appearing  fever, weakness, headache, flu-like symptoms, cough, sore throat, muscle pain, nausea, vomiting, diarrhea, and pain or burning at the wound site. As the virus spreads through the central nervous system, more severe symptoms develop.


Tick borne encephalitis (TBE)

Tick-borne encephalitis (TBE) is an illness triggered by a virus. The virus is transmitted to individuals primarily through bite from a tick carrying the virus or consumption of raw dairy products (milk and cheese) from infected goats, sheep, or cows.

Symptoms of tick-borne encephalitis may include flu-like symptoms  approximately one week after a tick bite such as:

  • fever
  • fatigue
  • headache
  • body aches
  • nausea
  • vomiting
  • loss of appetite

While these symptoms usually resolve on their own, in some cases, the virus can progress to cause more severe symptoms due to inflammation of the brain and/or spinal cord and leading to confusion and sensory disturbances. Tick-borne encephalitis can result in fatalities in severe cases. 

Some symptoms can be:

  • severe headache
  • sensitivity to light
  • seizures
  • altered behavior/ speech
  • weakness/ paralysis in parts of the body


TBE virus is prevalent in regions spanning from western and northern Europe to northern and eastern Asia. Travelers to these areas may be at risk of infection. Ticks carrying the TBE virus are most active during warmer months (April through November), particularly in forested areas. Individuals who engage in outdoor activities in or near forests are at heightened risk of tick bites.

For travelers visiting countries where tick-borne encephalitis is prevalent and planning outdoor activities, it is advisable to consider receiving the TBE vaccine. The vaccine typically entails two injections, offering protection for approximately one year, with a third injection extending protection to about three years. The initial injection should be administered at least one month before travel.


Herpes infection

Herpes simplex encephalitis (HSE) arises when the herpes simplex virus (HSV) causes acute or subacute onset of cerebral dysfunction and comes in two variants: HSV1 and HSV2.  HSV1 primarily affects the mouth and throat, often without symptoms early in life, but can later manifest as genital herpes. HSV2 is predominantly associated with genital herpes in adolescents and adults due to sexual transmission.

Approximately 90% of adults contract HSV1 at some point, with the virus establishing a hidden infection in sensory nerves, such as the trigeminal ganglia, following initial infection. Periodically, the virus may reactivate, resulting in visible lesions like cold sores.

Although HSV is widespread, HSE is rare. The exact route by which HSV gains entry to the brain remains unclear, with hypotheses suggesting blood circulation or nerve transmission lacking conclusive evidence.

However the virus gets into the brain, it causes serious damage during the illness. At first, it targets the  limbic cortex before spreading to frontal and temporal lobes causing  damaging tissue and brain swelling, leading to different symptoms.


Symptoms of HSE typically develop gradually over several days, varying based on factors like patient immunity. Initially resembling flu-like symptoms, HSE progresses to neurological deterioration. Untreated, symptoms worsen and may result in death. Common manifestations include:

  • headache
  • confusion
  • nausea
  • fever
  • seizures
  • sleepness 


Lumbar puncture

The main diagnostic procedure is lumbar puncture. This procedure involves taking a small sample of cerebrospinal fluid (CSF) around the brain and spinal cord for testing in the laboratory and  to detect the virus’s genetic material in the CSF, even if blood tests are normal. This test is usually effective within 10 to 20 days after the onset of neurological symptoms, after which it may become negative. 

False negatives may occur if the PCR test is performed too early, so a repeat test should be done at least four days after symptom onset before considering discontinuing treatment. Nonetheless, a PCR test should be conducted as soon as possible in all suspected cases of HSE.

Brain imaging using a computerized tomography (CT) scan can show changes in the brain, but it may not always provide definitive results. For a clearer understanding, a magnetic resonance imaging (MRI) scan is preferred. An MRI offers better visualization of the temporal lobe, which is commonly affected in encephalitis, allowing clinicians to identify changes more accurately. While MRI abnormalities are common in HSE patients, a normal MRI does not necessarily rule out the condition. 



Better health: viral encephalitis: https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/viral-encephalitis#symptoms-of-viral-encephalitis

NIH: Viral encephalomyelitis: https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/viral-encephalitis#symptoms-of-viral-encephalitis

Johns Hopkins medicine: Types of encephalitis: https://www.hopkinsmedicine.org/health/conditions-and-diseases/types-of-encephalitis

ScienceDirect: Encephalomyelitis: https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/encephalomyelitis

Mayo clinic: Polio: https://www.mayoclinic.org/diseases-conditions/polio/symptoms-causes/syc-20376512

CDC: What is Polio: https://www.cdc.gov/polio/what-is-polio/index.htm

World Health Organization: Poliomyelitis: https://www.who.int/news-room/fact-sheets/detail/poliomyelitis

NHS: Rabies: https://www.nhs.uk/conditions/rabies/

MedicalNewsToday: What you need to know about rabies: https://www.medicalnewstoday.com/articles/181980

WebMD: What is Rabies: https://www.webmd.com/a-to-z-guides/what-is-rabies

Mayo clinic: Rabies: https://www.mayoclinic.org/diseases-conditions/rabies/symptoms-causes/syc-20351821

CDC: Tick borne encephalitis: https://wwwnc.cdc.gov/travel/diseases/tickborne-encephalitis


NHS: Tick borne encephalitis: https://www.nhs.uk/conditions/tick-borne-encephalitis/

NIH: Herpes simplex enchephalitis: https://www.ncbi.nlm.nih.gov/books/NBK557643/

ScienceDirect: Herpes simplex virus-1 in the brain: https://www.sciencedirect.com/science/article/pii/S0966842X20300743

Encephalitis international: Herpes simplex virus encephalitis: https://www.encephalitis.info/types-of-encephalitis/infectious-encephalitis/herpes-simplex-virus-encephalitis/


Verified by Dr. Petya Stefanova