Etiology of Viral Encephalitis

Various Etiology of Viral Encephalitis:
a. Epidemic Viral infection :
1. Group enteroviruses, = poliomyelitis, coxsackie virus, ECHO virus.
2. Group Arbo virus, = equire western encephalitis, St. louis encephalitis, Eastern equireencephalitis, Japanese B encephalitis, Murray valley encephalitis
b. Sporadic Viral infections : rabies, herpes zoster, lymphogranuloma, mumps, limphotic, choriomeningitis and other types that are considered caused by a virus but it is not yet clear.
c. Post-infection encephalitis, post morbili, post-varicella, rubella post, post-vaccinia, pascamononucleosis, infectious and other types of respiratory tract infections that follow are not specific.

The most frequent cause of encephalitis is an infection due to a virus. A few examples include:
a. Herpes simplex virus (HSV-1, HSV-2)
b. In addition to the herpes virus: varicella zoster virus (VZV), cytomegalovirus (CMV), Epstein-Barr virus (EBV), human herpes virus 6 (HHV6)
c. adenovirus
d. influenza A
e. C enteroviruses, poliovirus
f. Measles, mumps and rubella virus
g. rabies
h. Arbovirus example, Japanese B encephalitis, St. Louis encephalitis virus, West Nile virus encephalitis, Eastern, Western, and Venezuelan equine encephalitis virus,
i. Bunyaviruses for example, La Crosse strain of California virus
j. Reoviruses eg, Colorado tick fever virus
k. For example arenaviruses, lymphocytic choriomeningitis virus.
l. Retroviruses such as human immunodeficiency virus-1/2 (HIV-1/2).

Encephalitis has two forms, which are categorized by two ways a virus can infect the brain:
a. Primary encephalitis. This occurs when the virus directly attacks the brain and spinal cord. This can happen at any time (sporadic encephalitis), so that it becomes an outbreak (epidemic encephalitis).
b. Secondary encephalitis. This happens when the first virus to infect other parts of the body then enters the brain.

Bacterial and parasitic infections such as toxoplasmosis can cause encephalitis in people who have weakened immune systems. Here are some of the more common causes of encephalitis:

A.Virus herpes
Some herpes viruses that cause common infections can also cause encephalitis. These include: Herpes simplex virus. There are two types of herpes simplex virus (HSV) infection. HSV type 1 (HSV-1) more often causes cold sores or fever blisters around your mouth. HSV type 2 (HSV-2) more often causes genital herpes. HSV-1 is the most important cause of fatal sporadic encephalitis in the United States, but also rare. Varicella-zoster virus. The virus responsible for chickenpox and shingles. These numbers can cause encephalitis in adults and children, but tend to be mild. Epstein-Barr virus. The herpes virus that causes infectious mononucleosis. If encephalitis develops, usually mild, but can be fatal in a small number of cases.

B. Infection in Children
In rare cases, secondary encephalitis virus infection occurs after the child and can be prevented with vaccines, including: Measles (rubeola), mumps, German measles (rubella). In such cases of encephalitis may be caused by a hypersensitivity reaction.

C. Arboviruses
The virus is transmitted by mosquitoes and ticks (Arboviruses) in recent years, resulting in epidemic encephalitis. Animal organisms that transmit disease from one host to another is called a vector. Mosquitoes are vectors for the transmission of encephalitis from birds or rodents to humans. This type of encephalitis, is quite rare