Japanese Encephalitis

Introduction

• Prevalence: Most common preventable cause of mosquito-borne encephalitis in Asia, Australia, and the western Pacific.
• Related Viruses: West Nile virus, St. Louis encephalitis virus, tick-borne encephalitis virus, Powassan virus
• Transmission: Via Culex mosquitoes, primarily in agricultural settings like farms and rice paddies, but possible in urban areas under certain conditions.
  • Transmission Cycle:
    • Mosquitoes: Primarily Culex species
    • Intermediate Hosts: Wading birds and pigs
  • Infection Process:
    • Mosquitoes feed on infected animals, then bite humans, transmitting the virus.
    • Humans are dead-end hosts: they do not develop high enough levels of the virus in their bloodstream to infect other mosquitoes.
  • Human-to-Human Transmission:
    • Extremely rare, only possible through blood transfusion.
    • Infected individuals should avoid donating blood and bone marrow for 120 days post-infection.
  • Not Spread By(as per CDC):
    • Coughing, sneezing, or touching
    • Touching live animals
    • Handling live or dead infected animals (use gloves or double plastic bags if disposing of dead animals)
    • Eating infected animals (ensure meat is fully cooked)

Symptoms of Japanese Encephalitis

Incubation Period: Typically 5–15 days from infection to illness onset.

Initial Symptoms

• Fever
• Headache
• Vomiting

Progression of Symptoms

• Disorientation
• Weakness
• Coma

Common Symptoms in Children

• Seizures

Asymptomatic Infections

• More than 99% of infected individuals do not show symptoms or have only mild symptoms.

Neurologic Illness

• Less than 1% of infected individuals develop neurologic illness.
• Symptoms include encephalitis (inflammation of the brain).
• High mortality rate: about 20–30% of encephalitis patients die.

Long-term Effects

• 30%-50% of survivors of encephalitis continue to experience movement, thinking, or behavioral symptoms.

Etiology

• Virus: Single-stranded RNA virus, closely related to the West Nile flavivirus.
• Vector: Culex mosquito species, particularly Culex tritaeniorhynchus.
• Hosts: Intermediate hosts include pigs and wading birds, while humans are dead-end hosts.

Epidemiology

• Incidence: 30,000 to 50,000 cases globally each year.
• Severe Disease: Occurs in about 1 in 250 infections.
• Transmission Seasonality: Higher risk during the rainy season and pre-harvest period in rice-cultivating areas.
• High-Risk Areas: 24 countries in South-East Asia and the Western Pacific, affecting over three billion people
• Risk Groups:
  • Travelers: Higher risk for those staying in rural or agricultural areas.
  • Children: Higher susceptibility and more severe disease outcomes.
  • Residents of Endemic Areas: Typically acquire immunity by adulthood.
• Vaccination Impact: Routine childhood vaccination in Japan, Korea, and Taiwan has nearly eliminated risk in vaccinated individuals.

Pathophysiology

• Initial Propagation: Virus attaches to host cell membranes, propagates at the bite site and nearby lymph nodes.
• Viremia: Leads to subclinical disease in most cases; neuroinvasive disease develops if the virus crosses the blood-brain barrier.
• Neurologic Effects: Direct neurotoxicity and altered neuro stem cell development can occur.

History and Physical Exam

• History: Recent mosquito exposure in endemic areas.
• Incubation Period: 6 to 8 days on average, ranging from 4 to 15 days.
• Initial Symptoms: Nonspecific fever, headache, nausea, vomiting, diarrhea, myalgias.
• Progression: Symptoms can advance to encephalitis, including altered mental status, agitation, confusion, psychosis, headache, meningismus in adults, and seizures in children.
• Neurologic Manifestations: Dystonia, choreoathetoid movements, mutism, flaccid paralysis.

Evaluation

• Neuroimaging: MRI or CT may reveal bilateral thalamic edema, lesions, or hemorrhage.
• Lumbar Puncture: Elevated opening pressure, elevated protein, normal glucose.
• Blood Tests: Leukocytosis, hyponatremia.
• Specific Testing: Detection of Japanese encephalitis virus IgM via ELISA on serum or CSF.

Treatment and Management

• No Antiviral Therapy: Management is limited to supportive care.
• Supportive Care: IV fluids, antipyretics, anticonvulsants for seizure control.
• Prevention: Avoid mosquito bites using protective clothing, DEET or permethrin repellents, and mosquito nets.
• Vaccination: Recommended for high-risk travelers and those spending significant time outdoors in endemic areas.

Differential Diagnosis

• Other Encephalitides: Murray Valley encephalitis, West Nile virus encephalitis, St. Louis encephalitis, Herpes simplex encephalitis.
• Other Conditions: Equine encephalitides, Ehrlichiosis, enterovirus meningitis, typhoid fever, dengue fever, malaria, brain abscess, tuberculous meningitis, Nipah virus infection, Rocky Mountain spotted fever, fungal meningitis, leptospirosis, neurocysticercosis, amebic meningoencephalitis, lupus with CNS involvement, CNS tumor, cerebrovascular accident.

Prognosis

• Encephalitis Progression: 1% of infections progress to encephalitis.
• Mortality Rate: 20% to 30% for encephalitis cases.
• Long-term Sequelae: 30% to 50% of survivors experience permanent neurological or psychiatric issues, such as paralysis, recurrent seizures, or impaired ability to perform daily activities.

Prevention of Japanese Encephalitis

Vaccination

• Vaccine Available in Australia: Imojev and JEspect
  • Imojev: A live attenuated vaccine
  • JEspect: An inactivated vaccine
• Cost: Prices vary, but generally range between AUD 200 to AUD 300 for a full course (subject to change and may vary by provider).
• Dosing and Schedule:
  • Imojev: Single dose provides long-term protection; booster doses are not typically required.
  • JEspect: Requires two doses administered 28 days apart. A booster dose may be recommended after 1-2 years for ongoing protection, especially for individuals at continued risk.
• Vaccination Recommendations
  • Intermediate to Long-Term Travelers:
    • Stay Duration: One month or more in endemic areas during transmission season.
    • Activities: Spending substantial time outdoors in rural/agricultural areas.
    • Living Conditions: Staying in accommodations without air conditioning, screens, or bed nets.
  • Short-Term Travelers:
    • High-Risk Activities: Engaging in outdoor activities or staying in high-risk environments.
    • Outbreak Regions: Visiting areas with known JE outbreaks.
    • Uncertain Itineraries: Travelers with unpredictable travel plans or destinations.

Other Preventive Measures

1. Avoid Mosquito Bites:
   • Timing: Mosquitoes that transmit Japanese encephalitis typically bite between dusk and dawn.
   • Clothing: Wear long sleeves, long pants, socks, and closed-toe shoes.
   • Repellents: Use insect repellents containing DEET, picaridin, or oil of lemon eucalyptus (PMD). Apply on exposed skin and clothing.
   • Permethrin Treatment: Treat clothing and gear, such as boots, pants, socks, and tents, with permethrin or purchase permethrin-treated clothing and gear.
2. Environmental Measures:
   • Sleeping Arrangements: Use air-conditioned rooms or ensure that sleeping areas are well-screened or use mosquito nets.
   • Mosquito Nets: Use insecticide-treated bed nets if accommodations are not air-conditioned or screened.
   • Insecticides: Use indoor insecticide sprays, mosquito coils, or vaporizing devices during peak mosquito activity times.
3. Avoiding Mosquito Habitats:
   • Locations: Be aware of high-risk areas such as agricultural settings, rice paddies, and areas with standing water.
   • Timing: Limit outdoor activities during peak mosquito biting times (dusk and dawn).
4. General Travel Advice:
   • Pre-Travel Consultation: Visit a travel health clinic or general practitioner 4-6 weeks before departure to discuss vaccination and preventive measures.
   • Awareness and Preparedness: Stay informed about the current risk levels in specific regions and follow public health advisories.
5. Post-Exposure Measures:
   • Symptom Monitoring: Be vigilant for symptoms such as fever, headache, nausea, vomiting, and seek immediate medical attention if symptoms develop.
   • Prompt Medical Attention: Early recognition and supportive care are crucial for reducing the risk of severe outcomes if infected.