Encephalitis is the medical term for inflammation of the brain. It is most commonly due to infections and the majority of these cases is due to a viral infection. Therefore the term encephalitis is almost always taken to mean viral encephalitis – infection of the brain tissue with a virus. It should not be confused with meningitis which is inflammation of the linings around the brain and spinal cord. Both conditions, encephalitis and meningitis, can present with similar symptoms despite being two separate conditions. Encephalitis can however present with meningitis in which case it is known as meningoencephalitis. Encephalitis is not a common condition but is a serious infection that needs to be monitored. Most cases, however, resolve on its own with little or no treatment if a person is healthy and not immune deficient.
Causes of Viral Encephalitis
Viral encephalitis is caused by a number of different types of viruses. These viruses enter the body through various ways. It replicates in tissues throughout the body and multiplies in large numbers outside the brain. The viruses then reach the brain by traveling via the :
- bloodstream – hematogenous dissemination.
- nerve pathways – retrograde neuronal dissemination.
The viruses are not limited to only certain parts of the brain. It can infect the cerebrum, cerebellum and brain stem.
Types of Encephalitis
Primary encephalitis iscaused by specific viruses attacking the brain tissue. Another type of encephalitis known as secondary encephalitis is caused by an immune reaction. It is also referred to as post-infectious encephalitis. Here the immune system attacks the brain tissue by incorrectly identifying some of the brain proteins as being viral proteins. Immunologic encephalitis is a complication of viral encephalitis and occurs even after the virus has been eradicated from the body.
List of Viruses
There are a number of different viruses that can causes viral encephalitis.
- Herpes simplex virus (HSV) type 1 and 2
- Human herpesvirus-6
- Varicella zoster virus (chickenpox virus)
- Mumps virus
- Measles virus
- Rubella virus (German measles virus)
- Arborviruses – about 20 types can causes viral encephalitis
- Alphaviruses like eastern equine encephalitis (EEE), western equine encephalitis (WEE), Venezuelan equine encephalitis (VEE)
- Flaviviruses like Japanese B encephalitis virus, West Nile virus, St Louis encephalitis,dengue virus, East tick-borne encephalitis, Central European tick-borne encephalitis and Powassan encephalitis viruses.
- Picornaviruses like coxsackievirus A and B, poliovirus and hepatitis A virus (HAV)
- Arenaviruses like the Lassa virus and lymphocytic choriomeningitis virus
- Rabies virus
- Chikungunya virus
The herpes simplex viruses are by far the most common cause of encephalitis – herpes simplex encephalitis (HSE).
There are many ways by which these viruses are transmitted. Some of these involve vectors such as animals and insects. Depending on the type of virus, outbreaks may occur only in certain geographical regions and at specific times of the year.
- Human-to-human direct contact is the main way that the most common encephalitis viruses are spread. This includes the herpes simplex, human herpesvirus 6, mumps, measles, rubella and varicella zoster viruses.
- Blood transfusions and organ transplantation – western Nile virus.
- Rodents – Lassa virus and lymphocytic choriomeningitis virus
- Bats and pigs – nipah virus
- Dogs and wild animals – rabies virus
- Mosquitoes – eastern equine virus , western equine virus, St Louis encephalitis virus, Japanese encephalitis virus, west Nile virus
- Ticks – Far East encephalitis virus, Central European encephalitis virus, Powassan virus, Colorado tick fever virus
There may be a greater chance of contracting viral hepatitis based on age, geographical location and pre-existing chronic diseases. Therefore people who are a greater risk includes :
- Age is a major risk factor with children and the elderly being the highest risk groups for contracting most types of viral encephalitis. Some viruses like the herpes simplex viruses is more frequently seen in young to middle aged adults within the 20 to 40 year age group.
- Chronic conditions such as diabetes mellitus, HIV/AIDS and other diseases that weaken the immune system increases the chance of contracting viral encephalitis.
- Regional risks depends on the type of virus and vectors particularly with insects like mosquitoes and ticks. People living in these regions who spend long hours in the outdoors are at a greater risk.
- Seasonal risks also depends on specific types of viruses and the vectors, particularly mosquitoes, that are responsible for transmission.
These risk factors should not detract from the fact that a person who is seemingly low risk may nevertheless contract viral hepatitis.
Signs and Symptoms
The main symptoms are similar to that of meningitis. It includes :
- Altered mental status – confusion, agitation, personality changes.
- Muscle aches
- Joint pains
Other symptoms such as seizures, numbness, paralysis, vision problems, difficulty speaking, disorders of smell and taste, hallucinations and loss of consciousness are seen with more severe cases of viral encephalitis or arises as a complication.
Milder cases of viral hepatitis are largely self remitting and will resolve on its own within days without requiring intensive treatment. However, a few conservative measures are helpful in the management of viral encephalitis. This includes :
- Plenty of fluids and a balanced diet.
- Bed rest.
- Limiting contact with others.
- Anti-inflammatory drugs for headaches, body pains and fever.
Antiviral drugs such as acyclovir are effective in treating viral encephalitis. These drugs should be limited to more severe types of encephalitis. Immune compromised patients like those with HIV/AIDS and long term diabetes mellitus may require medication earlier as the immune system is not able to adequately protect the body.
Viral hepatitis can be prevented in many cases although this depends on the type of virus responsible for the infection as well as geographical and seasonal factors. Preventative measures also depends on the type of virus involved and vectors of spread. These measures include :
- Maintaining one’s general health through a balanced diet, regular exercise and proper rest. The immune system is one of the best defenses and its effectiveness is dependent on the general health of the person.
- Vaccinations are a very effective preventative measure. Although vaccines are not available for every type of encephalitis virus, some of the common viral infections like mumps and measles are preventable with vaccinations.
- Insect control, the use of repellents and protective wear are important for preventing mosquito-borne and tick-borne encephalitis viruses.
- Practicing good hygiene by using washing hands regularly with antiseptic solutions and not sharing personal items.