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Japanese Encephalitis - Community Medicine (MBBS)

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1. Definition and Causative Agent

• The envelope glycoprotein contains specific and cross-reactive neutralizing epitopes
• Several genotypes exist with different geographical distribution, but all belong to the same serotype and are similar in virulence and host preference
• After an infectious mosquito bite, initial viral replication occurs in local and regional lymph nodes, then viral invasion of the CNS occurs via blood

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2. Epidemiology - Global

• Leading cause of viral encephalitis in Asia, occurring in 24 Asian and Western Pacific countries
• Annual incidence ranges from <10 to >100 per 100,000 population
• Estimated ~68,000 clinical cases globally per year, with up to 20,400 deaths
• Vast majority of cases are in children <15 years; ~10% among those >60 years (waning immunity)
• Major outbreaks occur every 2-15 years
• Largely declining in Japan, Korean peninsula, and parts of China due to immunization
• Increasingly reported from Bangladesh, India, Nepal, Pakistan, northern Thailand, Vietnam
• Rare outside endemic areas; seen in travellers returning from endemic zones

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3. Problem in India

• First recognized by serological surveys in 1955 in Tamil Nadu
• Endemic in 21 states
• High-burden states reporting annual outbreaks: Assam, Bihar, Haryana, Uttar Pradesh, Karnataka, West Bengal, Tamil Nadu (contribute ~55% of cases and deaths)
• Maximum reporting states: Andhra Pradesh, West Bengal, Assam, Tamil Nadu, Karnataka, Bihar, Maharashtra, Manipur, Haryana, Kerala, UP
• ~375 million population at risk in India
• JE is reported under the umbrella of Acute Encephalitis Syndrome (AES)
• 2016 data: 11,651 AES cases with 1,301 deaths; included 1,676 JE cases with 283 deaths

State-wise JE cases and deaths in India (2016-2018):

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4. Epidemiological Features (Transmission Cycle)

Basic Transmission Cycles (Zoonotic):

• (a) Pig → Mosquito → Pig
• (b) Ardeid birds (Herons/Egrets) → Mosquito → Ardeid birds

(a) Animal Hosts

• Pigs are the primary amplifying hosts - they develop high-level viremia sufficient to infect mosquitoes
• Ardeid birds (herons, egrets) maintain the basic transmission cycle
• Other animals (cattle, horses, sheep) may be infected but develop low viremia and are poor amplifying hosts

(b) Vector (Mosquito)

• Principal vector: Culex tritaeniorhynchus (paddy field/rice field mosquito)
• Other vectors: Culex vishnui, Culex gelidus
• These are outdoor resting (exophilic) mosquitoes - this is why indoor residual spray (IRS) is NOT effective
• Breeding habitat: rice fields, irrigation canals, shallow ground water
• Feeding time: dusk to dawn (crepuscular and nocturnal)
• Transmission intensifies during the rainy season when vector population increases

(c) Man (Host)

• Most infections are subclinical (inapparent)
• Ratio of inapparent to clinical infection: approximately 300:1 (varies from 25:1 to 1000:1 in literature)
• Children <15 years most susceptible
• Immunity after natural infection appears to be long-lasting
• Infection does not provide cross-protection against other flaviviruses

(d) Environment

• Transmission is seasonal - related to the rainy season (July-October in India)
• Rural agricultural areas with flooding irrigation (paddy fields) are highest risk
• Spread to new areas correlated with agricultural development + irrigation programmes

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5. Clinical Features

• Incubation period: 5-15 days
• Three clinical phases:

Prodromal Phase (2-4 days)

• Fever, headache, malaise, nausea, vomiting
• Behavioral changes in children

Acute Encephalitic Phase

• High fever, severe headache, convulsions
• Signs of meningeal irritation (neck stiffness, Kernig's sign)
• Altered consciousness, coma
• Tremors, coarse involuntary movements
• Mask-like facies (Parkinson-like features)
• Characteristic: Acute flaccid paralysis can occur

Late Phase / Outcome

• Recovery (with or without neurological sequelae)
• Death (case fatality rate: 20-30% in clinical cases)
• ~30-50% of survivors have permanent neuropsychiatric sequelae - cognitive impairment, behavioral problems, motor deficits, seizure disorders, psychiatric illness

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6. Diagnosis

• Primarily clinical, confirmed by serology
• JE-specific IgM antibody detection in CSF or serum (IgM capture ELISA) - gold standard
• Viremia resolves by the time patient presents, so virus isolation is rarely positive
• CSF: lymphocytic pleocytosis, raised protein, normal to slightly reduced glucose
• CT/MRI brain: bilateral thalamic lesions (characteristic but not pathognomonic)
• EEG: diffuse slow wave activity

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7. Treatment

• No specific antiviral treatment (no specific cure)
• Treatment is supportive and symptomatic:
  • Antipyretics for fever
  • Anticonvulsants for seizures
  • IV fluids for dehydration
  • Ventilatory support if needed
  • Management of cerebral edema (mannitol)
  • Prevention and treatment of secondary bacterial infections
• Early case management is vital to minimize complications and death

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8. Prevention and Control

(A) Vector Control

• Larvicidal measures: use of larvivorous fish (Gambusia, Lebistes) in rice fields/irrigation channels
• Biological control
• Malathion outdoor fogging for outbreak control (since vectors are outdoor resters, IRS is ineffective)
• Reduction of mosquito breeding sites
• Personal protection:
  • Bed nets (treated where possible)
  • Full-body covering clothing, especially at dusk to dawn
  • Mosquito repellents

(B) Animal Reservoir Control

• Keep pigs away from human dwellings (in pigsties), especially during dusk to dawn biting hours
• Vaccination of pigs has been tried but not widely feasible

(C) Vaccination (Most Important Control Measure)

• JE vaccination is the cornerstone of prevention
• SA 14-14-2 live attenuated vaccine - most widely used in Asia, including India
• Recommended for children 1-15 years of age
• Other vaccines: inactivated Vero cell-derived vaccine (IXIARO)
• Under Universal Immunization Programme (UIP) in India - JE vaccine included for endemic districts
• Phase-wise rollout in high-burden districts

(D) Health Education and IEC

• Community awareness about signs/symptoms - early reporting
• Correct knowledge of breeding sites, mosquito protection
• Information about available health facilities
• Behaviour Change Communication (BCC)

(E) Surveillance

• Strengthening surveillance through sentinel sites in tertiary health care institutions
• Epidemiological monitoring for effective implementation
• JE cases reported under AES umbrella

(F) Government of India Initiatives

• Need-based assistance to states
• Training programmes and social mobilization
• Capacity building
• Technical support on request from state health authorities

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9. Summary of Key Points for MBBS Exams

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10. Recent Evidence

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National Immunization Schedule (NIS) - Community Medicine (MBBS)

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Background

• EPI (Expanded Programme on Immunization) launched by WHO globally in May 1974; launched in India in January 1978
• UIP (Universal Immunization Programme) launched in India on November 19, 1985, dedicated to Smt. Indira Gandhi
• Target: Universal immunization coverage of eligible population
• UIP became part of CSSM (1992) → RCH Programme (1997) → National Health Mission (current)

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TABLE 43: National Immunization Schedule (NIS) - India (2020)

FOR PREGNANT WOMEN

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FOR INFANTS

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FOR CHILDREN (Booster doses)

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PENTAVALENT VACCINE - Key Note

• Replaces separate DPT, Hepatitis B, and Hib conjugate vaccines
• Given at 6, 10, 14 weeks
• If pentavalent is used, do NOT give DPT, Hep B, and Hib separately at those visits

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Quick-Reference Age Chart

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Diseases Covered Under UIP

1. Tuberculosis (BCG)
2. Diphtheria (Pentavalent/DPT)
3. Pertussis/Whooping cough (Pentavalent/DPT)
4. Tetanus (Pentavalent/DPT/TT)
5. Poliomyelitis (OPV + IPV)
6. Hepatitis B (Pentavalent/Hep B)
7. Haemophilus influenzae type b disease (Pentavalent)
8. Measles (MR)
9. Rubella (MR)
10. Japanese Encephalitis** (endemic districts)
11. Rotavirus diarrhoea (RVV) - select states
12. Pneumococcal disease (PCV) - select states

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IAP Schedule (vs NIS) - Additional Vaccines Not in UIP

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Important Rules / Mnemonics for Exams

BCG

• Site: Left upper arm, intra-dermal
• Dose at birth: 0.05 ml; after 1 month: 0.1 ml
• Can be given up to 1 year of age

OPV Zero Dose

• Given at birth in institutional deliveries before discharge
• Not to be counted toward primary series; separate from OPV 1, 2, 3

IPV

• Fractional IPV (fIPV) - 0.1 ml intra-dermal (not IM)
• Two doses at 6 and 14 weeks
• Right upper arm

TT in Pregnancy

• TT-1: Early pregnancy
• TT-2: 4 weeks after TT-1
• Booster: If 2 TT doses received in previous pregnancy within last 3 years
• Purpose: Prevention of neonatal tetanus

Vitamin A

• First dose: 1 lakh IU at 9 months with MR-1
• Subsequent doses: 2 lakh IU every 6 months (16 months, 22 months... up to 5 years)
• Total: 1 + 8 = 9 doses

Cold Chain

• Vaccine storage temperature: +2°C to +8°C (refrigerator)
• Oral polio vaccine (OPV): Can also be stored at -20°C (frozen)
• Heat-sensitive vaccines: OPV > MMR > BCG > Measles > DPT > Hep B (least heat-sensitive)

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Key Exam Points

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