Japanese encephalitis virus

Japanese Encephalitis Virus (JE)
Scientific classification
Phylum: Flaviviridae Genus: Flavivirus Species: Japanese encephalitis virus

General information and Symptoms

Originally named Japanese B encephalitis virus in order to aid in distinguishing this species of encephalitis with an agent causing Von Economo's type A encephalitis species, it has since been modified to a more simple name without the B. Japanese encephalitis (JE) is a virus that infects the central nervous system, which consists of the brain and spinal cord. It may range from mild to acute infection. Mild Symptoms include flu-like illness that may include:

• Headaches
• Agitation
• Feeling tired
• Nausea
• Vomiting
• Chills
• Fever

A severe infection symptoms may include mild symptoms as well as:

• Rapid onset
• Stupor
• Disorientation
• Coma
• Tremors
• Occasional convlusions (occurs more often in infants)
• Spastic paralysis
• Flaccid paralysis (occurs in rare instances)

As the infection progresses without treatment it may reach an acute level. When such a high level of infection occurs, there are serious side affects which include moderate brain damage ,varying degrees of paralysis, as well as seizures and death.

Transmission and Epidemiology

Japanese encephalitis virus is considered an arthropod virus called an arbovirus. The vector that spreads this arbovirus is a mosquito.The Culicine mosquito from the genus Culex are responsible for many diseases such as Dengue fever, Yellow fever, Venezuelan equine encephalitis, as well as the Japanese encephalitis. Their eggs are laid in still water that is either clean water or contaminated with organic waste. These eggs are also resistant to dessication for several months. The first reported suspicion of JE was within the last century and first documented in horses as well as humans in Japan, which explains the origin of it's name. The virus was first isolated from human brain tissue in rabbits in 1924. The specific species of Culex mosquitos linked to the JE virus is the Culex (Cx) tritaeniorhynchus

Infection into a healthy human begins with an infected mosquito. This mosquito lands on a human's skin and bites the victim, this transmits the virus into the bloodstream and is able to cause viraemia, the virus being spread intially from the bite site which allows it access to the rest of the body through the circulatory system.

The way a mosquito can be infected with the virus is from feeding on infected humans, horses, and cattle. These are all hosts that are dead-end and due to high rates of fatality do not transmit the disease as readily, however, swine are largely asymptomatic hosts. The only exception is the high abnormalities and abortions of fetal swine in pregnant sows. Due to their lack of symptoms mosquitos are more likely to feed on a seemingly healthy pig. This causes the mosquito to be contaminated and become a vector. Infection in humans occur in the cochlea of the ear. The species that is most significant in the JE virus, C. tritaeniorhynchus, typically feeds on bovine animals. Despite suggestions of the spraying of pesticides to kill mosquito vectors and moving swine herds to more rural areas away from humans there is a belief among many that Japanese encephilitis will not be eliminated because the natural host for this virus is a bird. JE is the most prevalent of viral encephalitis in Asia with 30,000-50,000 cases reported each year, of those cases fatalities fall between 0.3-60%. There is a high risk of contracting this virus in rural areas that are endemic locations. Some cities have had success in conquering major epidemic outbreaks of JE, such as Thailand, Taiwan, Japan, China, and Korea. They have done this with vaccinations. While these countries, to a certain extent, have successfully contained this virus, some still have periodic outbreaks. The countries that fall into this category are Malaysia, Myanmar, India, Nepal, Cambodia, and Vietnam. Despite JE occuring mostly in asian, in 1998 in the mainland of northern Australia there has been 2 fatal cases of JE.

Pathology

Japanese Encephalitis is antigenically linked to several other flaviviruses and belongs to the family Flaviviridae. An Antigen is a substance that causes that causes the body to illicit an immune response such as the production of antibody through the introduction of a foreign substance such as a virus or bacteria into the body.