Encephalitis
Encephalitis means severe inflammation (swelling) of brain. Encephalitis is the brain inflammation ensuring from a viral infection and also bacterial infection. It often occurs with inflammation covering brain and spinal cord (meningitis).Due to Inflammation normal blood flow in the brain changes. Also occurs due to by mistake attack of immune system on the tissue (post-infectious encephalitis). Encephalitis ranges from mild to severe but sometimes may result to permanent neurological damage and death. As such it is rare disease that occurs, though there are several thousand cases of encephalitis (also called acute viral encephalitis or aseptic encephalitis) every year, experts think that many more cases go unreported since the symptoms of Encephalitis are so mild.
TYPES OF ENCEPHALITIES
Primary encephalitis- It involves direct viral infection on brain and spinal cord. It usually happen in isolated cases (sporadic) or may arise in many people at the similar time in the same area (epidemic). They carry an elevated risk for serious neurological damage and death and may occur in infants if the virus is passed from the mother to the infant at the time birth.
Secondary encephalitis- In this viral infection first occurs somewhere else in body and then travels to brain or due to reactivation of a latent virus. Here viruses become reactive when the immune system is suppressed.
Causes
The viruses that lead to infectious encephalitis can be kept into three categories:
Common viruses: Viruses involved are herpes simplex virus (HSV) type 1 and type2 or the Epstein Barr virus (EBV). Widely spread in large population.
Childhood viruses: Responsible for causing childhood infections, like mumps, measles and rubella.
Arboviruses: Are transmitted by blood sucking insects, such as mosquitoes and ticks. Some examples of arboviruses are Japanese encephalitis, tick-borne encephalitis and West Nile encephalitis, Eastern equine encephalitis, Western equine encephalitis’s, Louis encephalitis,La Crosse encephalitis. Mosquitoes act as vectors for the spread of encephalitis from small creatures like birds and rodents to humans. Some Ticks also act as a vector and carry such viruses that cause brain inflammation, and causes Russian spring-summer encephalitis which is more common in China, Korea, and the eastern areas of Russia.
The blood brain barrier of brain protects it from viral infection n other toxic materials, it is a thick membrane that acts as a barrier and filters out impurities from blood prior to allowing it to go into the brain. But due to some reasons these viruses passes the blood brain barrier and infect the tissues of brain. After passing the blood brain barrier, virus enters the blood cells and damage them leading to a loss of normal brain function. If not treated, encephalitis may result in coma and finally death.
Post infectious encephalitis is a rare viral infection complication, which occurs following vaccine-preventable childhood viral infections, including: measles, mumps or chickenpox, germane measles (rubella). In this case encephalitis occurs due to hypersensitivity, an overreaction of immune system to a foreign substance.
It may be caused by a bacterial infection, spreading directly to the brain (primary encephalitis), or may be a due to complications of an existing infectious disease syphilis (secondary encephalitis).