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Japanese Encephalitis

Updated : February 23, 2024





Background

The most prevalent preventable cause of mosquito-borne encephalitis in Asia, Australia, and the western Pacific is Japanese encephalitis. The Culex mosquito species transmit the virus through their bites. Transmission is more prevalent in agricultural regions such as rice paddies and farms, but it is also possible in urban areas under particular circumstances.

Despite the fact that most infections are asymptomatic, individuals who develop encephalitis symptoms have severe mortality and morbidity. Due to cerebral inflammation, symptomatic patients experience an altered mental status, get high fever, headaches, tremors, disorientation, and sometimes patients can also slip into a coma.

Movement abnormalities, neurologic impairments, and seizures are prevalent in particularly youngsters. Around 1 in 4 cases with symptoms are fatal. Most individuals who live in endemic regions will develop immunity by the time they reach adulthood.

There is no specific treatment beyond providing care, but an effective vaccine to prevent infection is available. It is suggested that high-risk travelers to endemic regions receive the vaccine. Many endemic regions have undertaken vaccination programs for children. The most effective protection is the avoidance of mosquito bites.

Epidemiology

Each year, around 30,000-50,000 cases of Japanese encephalitis are found worldwide. An estimated one in every 250 infections results in severe illness. Transmission of the illness peaks between May and October in temperate climates, although in temperate climates there is always a slight risk of infection.

Due to increasing mosquito vector populations, the risk of illness is greatest during the pre-harvest period, and in the rainy season. Transmission of this illness happens between dawn and dusk. 24 nations in the Western Pacific and South-East Asia have endemic transmission of the Japanese encephalitis virus, putting more than three billion people at risk of illness.

Major epidemics occur every two to fifteen years. In China alone, about 1 million cases were diagnosed during 1965-1975. Despite persistent infection in endemic birds and animals, the implementation of widespread childhood immunization programs in Taiwan, Korea and Japan has practically eradicated the danger among vaccinated individuals. The majority of reported cases in these regions currently involves unvaccinated travelers.

Anatomy

Pathophysiology

Attaching itself to host cell membranes, this virus initially spreads at the site of the bite and adjacent lymph nodes. Subsequently, viremia occurs, but in the majority of instances, the virus is cleared before entering the CNS, leading to subclinical illness.

Neuroinvasive illness develops if the virus is transferred hematogenously to the brain by breaching the blood-brain barrier. The Japanese encephalitis virus directly results causes neurotoxic effects and also has the ability to affect neuro stem cell development.

Etiology

Japanese encephalitis is a sickness transmitted by mosquitoes and caused by a single-stranded RNA virus that is closely linked to the West Nile flavivirus. Transmission of Japanese encephalitis is predominantly caused by Culex mosquito species, specifically Culex tritaeniorhynchus. The virus is sustained and multiplied by intermediate hosts, namely wading birds and pigs.

Humans are termed dead-end hosts because they do not typically produce sufficient viral levels to transmit the disease to mosquitoes. Most infections occur in rural regions due to the prevalence of amplifying hosts in agricultural settings, such as rice fields and farms, where irrigation lures in wading birds. Recent reports, however, indicate an increase in the prevalence of infections in suburban areas, particularly in China, South Korea, Taiwan, and Singapore.

This indicates that the recommended vaccinations for travelers should be broadened to cover some suburban areas. While most infections are transmitted by mosquitoes, there is some fear that intimate contact with sick pigs, which serve as amplifying hosts, may result in virus transmission without the involvement of a vector.

Genetics

Prognostic Factors

Although only 1/100 patients infected with this virus eventually get encephalitis, the mortality rate for the same is between 20%-30%. Other cases improve within 6-12 months, but 30%-50% have to deal with psychiatric and neurologic sequelae.

Clinical History

Physical Examination

Age group

Associated comorbidity

Associated activity

Acuity of presentation

Differential Diagnoses

Laboratory Studies

Imaging Studies

Procedures

Histologic Findings

Staging

Treatment Paradigm

by Stage

by Modality

Chemotherapy

Radiation Therapy

Surgical Interventions

Hormone Therapy

Immunotherapy

Hyperthermia

Photodynamic Therapy

Stem Cell Transplant

Targeted Therapy

Palliative Care

Medication

Media Gallary

References

https://www.ncbi.nlm.nih.gov/books/NBK470423/

Japanese Encephalitis

Updated : February 23, 2024




The most prevalent preventable cause of mosquito-borne encephalitis in Asia, Australia, and the western Pacific is Japanese encephalitis. The Culex mosquito species transmit the virus through their bites. Transmission is more prevalent in agricultural regions such as rice paddies and farms, but it is also possible in urban areas under particular circumstances.

Despite the fact that most infections are asymptomatic, individuals who develop encephalitis symptoms have severe mortality and morbidity. Due to cerebral inflammation, symptomatic patients experience an altered mental status, get high fever, headaches, tremors, disorientation, and sometimes patients can also slip into a coma.

Movement abnormalities, neurologic impairments, and seizures are prevalent in particularly youngsters. Around 1 in 4 cases with symptoms are fatal. Most individuals who live in endemic regions will develop immunity by the time they reach adulthood.

There is no specific treatment beyond providing care, but an effective vaccine to prevent infection is available. It is suggested that high-risk travelers to endemic regions receive the vaccine. Many endemic regions have undertaken vaccination programs for children. The most effective protection is the avoidance of mosquito bites.

Each year, around 30,000-50,000 cases of Japanese encephalitis are found worldwide. An estimated one in every 250 infections results in severe illness. Transmission of the illness peaks between May and October in temperate climates, although in temperate climates there is always a slight risk of infection.

Due to increasing mosquito vector populations, the risk of illness is greatest during the pre-harvest period, and in the rainy season. Transmission of this illness happens between dawn and dusk. 24 nations in the Western Pacific and South-East Asia have endemic transmission of the Japanese encephalitis virus, putting more than three billion people at risk of illness.

Major epidemics occur every two to fifteen years. In China alone, about 1 million cases were diagnosed during 1965-1975. Despite persistent infection in endemic birds and animals, the implementation of widespread childhood immunization programs in Taiwan, Korea and Japan has practically eradicated the danger among vaccinated individuals. The majority of reported cases in these regions currently involves unvaccinated travelers.

Attaching itself to host cell membranes, this virus initially spreads at the site of the bite and adjacent lymph nodes. Subsequently, viremia occurs, but in the majority of instances, the virus is cleared before entering the CNS, leading to subclinical illness.

Neuroinvasive illness develops if the virus is transferred hematogenously to the brain by breaching the blood-brain barrier. The Japanese encephalitis virus directly results causes neurotoxic effects and also has the ability to affect neuro stem cell development.

Japanese encephalitis is a sickness transmitted by mosquitoes and caused by a single-stranded RNA virus that is closely linked to the West Nile flavivirus. Transmission of Japanese encephalitis is predominantly caused by Culex mosquito species, specifically Culex tritaeniorhynchus. The virus is sustained and multiplied by intermediate hosts, namely wading birds and pigs.

Humans are termed dead-end hosts because they do not typically produce sufficient viral levels to transmit the disease to mosquitoes. Most infections occur in rural regions due to the prevalence of amplifying hosts in agricultural settings, such as rice fields and farms, where irrigation lures in wading birds. Recent reports, however, indicate an increase in the prevalence of infections in suburban areas, particularly in China, South Korea, Taiwan, and Singapore.

This indicates that the recommended vaccinations for travelers should be broadened to cover some suburban areas. While most infections are transmitted by mosquitoes, there is some fear that intimate contact with sick pigs, which serve as amplifying hosts, may result in virus transmission without the involvement of a vector.

Although only 1/100 patients infected with this virus eventually get encephalitis, the mortality rate for the same is between 20%-30%. Other cases improve within 6-12 months, but 30%-50% have to deal with psychiatric and neurologic sequelae.

https://www.ncbi.nlm.nih.gov/books/NBK470423/