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Japanese Encephalitis (JE) is zoonotic viral disease which is caused by JE virus. The virus is transmitted from animals, birds, pigs, particularly the birds belonging to family Ardeidae (eg. Cattle egrets, pond herons etc.) to man by  Vishnu group Culex vector. It may result in febrile illness of variable severity and  affects the central nervous system causing severe complications, seizures and even death. The case fatality rate of this disease is high and those who survive may suffer with various degrees of neurological sequelae.

  1. Why IS JE CALLED Zoonotic disease?

JE is basically a disease of animals. Pigs and birds, particularly those belonging to Family Ardeidae (e.g. cattle egrets, pond herons, etc.) are natural hosts. The virus is generally maintained in the enzootic form and appears as focal outbreaks under specific ecological conditions. Infection in human beings is caused as a result of spill-over of infection from zoonotic cycle. At low vector density level the virus circulates in ardied birds-mosquito ardied bird cycle. However, at the commencement of monsoon season or increased availability of surface area mosquito breeding e.g. paddy cultivate etc., the vector population builds up rapidly, the virus from wild birds through vector mosquito species spreads to peri domestic birds and then to mammals like cattle and pigs, etc. and eventually spills over to man.


JE virus infection presents classical symptoms similar to any other virus causing encephalitis. It may result in febrile illness of variable severity associated with neurological symptoms ranging from headache to meningitis or encephalitis. Symptoms can include headache, fever, meningeal signs, stupor, disorientation, coma, tremors, paralysis (generalized), hypertonia, loss of coordination, etc. Clinically it is difficult to differentiate between JE and other viral encephalitis. 


The JE virus is transmitted from animals, birds, pigs, particularly the birds belonging to family Ardeidae (eg. Cattle egrets, pond herons etc.) to man by Vishnu group Culex vector. Pigs play an important role in the natural cycle and serve as an amplifier host since they allow manifold virus multiplication without suffering from disease and maintain prolonged viraemia. Due to prolonged viraemia, mosquitoes get opportunity to pick up infection from pigs easily. Man is a dead end in transmission cycle due to low and short-lived viraemia. Mosquitoes do not get infection from JE patient.


Japanese encephalitis virus isolation has been made from a variety of mosquito species. Culicine mosquitoes mainly Culex vishnui group (Culex tritaeniorhynchus, Culex vishnui and Culex pseudovishnui) are the chief vectors of JE in different parts of India. Culex vishnui subgroup is very common, widespread and breed in water with luxuriant vegetation mainly in paddy fields and the abundance is related to rice cultivation, shallow ditches and pools.These vectors are primarily outdoor resting in vegetation and other shaded places but in summer may also rest in indoors.

Japanese encephalitis virus isolation has been reported from various mosquito species found in India, including:

  1. Culex tritaeniorhynchus
  2. Culex vishnui
  3. Culex pseudovishnui
  4. Culex bitaeniorhynchus
  5. Culex epidesmus
  6. Culex fuscocephala
  7. Culex gelidus
  8. Culex quinquefasciatus
  9. Culex whitmorei
  10. Anopheles barbirostris
  11. Anopheles paeditaeniatus
  12. Anopheles subpictus
  13. Mansonia annulifera
  14. Mansonia indiana
  15. Mansonia uniformis



The JE case is suspected as per clinical signs/symptoms and it has to be confirmed in laboratory as follows:-

Clinical: Acute onset of fever <7 days duration associated with  change in mental status (may include irritability, somnolence or abnormal behavior greater than that seen with usual febrile illness) and/or new onset of seizures (excluding simple febrile seizures).

Confirmatory test:- It has to be laboratory confirmed with any one of the following markers: 

  • Presence of IgM antibody in serum and/ or CSF to JE Virus
  • Four fold difference in IgG antibody titre in paired sera
  • Virus isolation from brain tissue 
  • Antigen detection by immunofluroscence
  • Nucleic acid detection by PCR


  1. What are the early warning signals for predicting an outbreak of JE?

          The clues for an impending outbreak can be picked up from following.

  • Prediction of high rainfall by the meteorological department, an unusual increase in the adult vector density.
  • Relative increase in pig population and water frequenting birds should alert the local officers. · Virus detected in the suspected animal hosts and in mosquitoes can also act as an indicator for warning a forthcoming outbreak.
  • Epidemiological data for the last 3-5 years would indicate the trend of the diseases in the specific area.
  1. What are the risk factors for JE outbreak in an area ?
  • Increase in susceptible population.
  • High density of Culex mosquitoes.
  • Presence of amplifying hosts such as pigs, water birds etc.
  • Paddy cultivation.



Management of Encephalitis is essentially symptomatic. To reduce severe morbidity and mortality, it is important to identify early warning signs (irritability, somnolence or abnormal behavior greater than that seen with usual febrile illness and/or new onset of seizures (excluding simple febrile seizures) and refer patients to health facility.

Currently, there is no specific antiviral treatment for Japanese encephalitis (JE) that can directly target the virus. Therefore, the management of JE primarily focuses on supportive care to relieve symptoms and complications. Here are the key aspects of treatment for Japanese encephalitis:

  1. Hospitalization: Severe cases of JE often require hospitalization for close monitoring and medical care. This is particularly important for patients with neurological complications or those experiencing severe symptoms.
  2. Supportive care: Supportive measures are provided to manage symptoms and help the patient's body fight the infection. These may include:
  3. Medications for fever and pain relief: Acetaminophen (paracetamol) may be given to reduce fever and relieve headache or body aches. Nonsteroidal anti-inflammatory drugs (NSAIDs) are generally avoided due to the risk of bleeding complications.
  4. Fluid management: Adequate hydration is essential, especially if the patient has high fever, vomiting, or diarrhea. Intravenous fluids may be administered if necessary.



As per Govt. of India guidelines, 2 doses of JE vaccine have been approved to be included in UIP to be given one along with measles at the age of 9 months and the second with DPT booster at the age of 16-24 months w.e.f. April, 2013.


JE viral activity has been widespread in India. The first evidence of presence of JE virus dates back to 1952. First case was reported in 1955.

. Here are some key points about the extent of the problem of Japanese encephalitis in India:

  1. Endemic regions: Japanese encephalitis is considered endemic in several states of India, especially in the northeastern and northern parts of the country.

Outbreaks have been reported from different parts of the country. It is endemic in 327 districts of 24 states.

  1. Seasonal outbreaks: JE cases in India often follow a seasonal pattern, with increased transmission during the monsoon and post-monsoon periods when mosquito populations are higher. Outbreaks typically occur from May to October, peaking during the rainy season.
  2. High burden of cases: India accounts for a significant proportion of JE cases globally. The exact number of cases can vary from year to year, but several thousand cases are reported annually. However, it is worth noting that the reported numbers may not fully reflect the actual burden due to underreporting and challenges in surveillance.
  3. Impact on vulnerable populations: Japanese encephalitis primarily affects children and individuals living in rural areas, especially those involved in agricultural activities. Children under the age of 15 are particularly susceptible to severe forms of the disease, and the infection can lead to long-term neurological complications or death.
  4. Vaccination efforts: In response to the burden of Japanese encephalitis, India has implemented vaccination programs in endemic areas. Vaccination coverage has been expanded in recent years, targeting children in endemic regions to reduce the incidence of the disease.
  5. Vector control measures: Mosquito control programs, including larval source reduction, use of insecticide-treated bed nets, and community-based initiatives, are important strategies for preventing the spread of JE in affected areas.

Efforts are ongoing to enhance surveillance, improve access to vaccination, and strengthen vector control measures to mitigate the impact of Japanese encephalitis in India. Public health authorities continue to work towards reducing the burden of the disease through comprehensive prevention and control strategies.



Prevention and control measures for Japanese Encephalitis (JE) involve a combination of strategies targeting both the vector and the human population. Here are some key approaches:

  1. Vaccination:

As per Govt. of India guidelines, 2 doses of JE vaccines have been approved in routine immunization for endemic districts -one along with measles at the age of 9 months and the second with DPT booster at the age of 16-24 months w.e.f. April, 2013.


  1. Vector Control: Mosquito control: Targeting mosquito populations is an important aspect of JE prevention. Measures include larval source reduction through the elimination or treatment of mosquito breeding sites, such as stagnant water sources. This can be achieved through environmental management, proper water storage practices, and the use of larvicides.
  2. Indoor residual spraying: The application of insecticides to indoor surfaces, particularly in areas with high mosquito densities, can help reduce the number of infected mosquitoes and minimize human-mosquito contact.
  3. Personal Protective Measures: Avoiding mosquito bites: Individuals should take precautions to minimize exposure to mosquitoes, particularly during peak biting times. This includes wearing long-sleeved clothing, using insect repellents on exposed skin, and staying in well-screened or air-conditioned accommodations.
  4. Use of mosquito nets: Sleeping under mosquito nets, especially in areas without access to insecticide-treated bed nets, provides an additional layer of protection against mosquito bites.
  5. Health Education and Awareness: Public health education campaigns play a vital role in raising awareness about JE, its transmission, and preventive measures. Promoting community participation and providing information on personal protection measures, vaccination, and vector control can empower individuals to take necessary precautions.

Note: Piggeries may be kept away (4-5 kms) from human dwellings.



  • JE vaccination in Routine vaccination was covered to 297 nos of districts and Adult vaccination covered for 31 nos of districts for the state of Assam, Uttar Pradesh and West Bengal.
  • Re-orientation training course on AES/JE case management is a continuing process. Such orientating training courses were carried out in endemic states.
  • Advisories to all the states are being sent to all the endemic states before the transmission session.
  • The diagnostic facilities have been strengthened to 154 Sentinel Surveillance Hospital (SSH)and 15 Apex Referral Laboratories (ARL). These have been supplied with diagnostic kits free of cost from National Institute of Virology (NIV), Pune.
  • The situation of all endemic states are reviewed before the transmission session. Guidelines were developed on AES/JE case management and on prevention and control of Entero-viruses which have been circulated to the states.
  1. What is Veterinary Based Surveillance?
  • By identifying the prevalence & density of pigs, ducks, and ardeid birds and detecting viral activity in susceptible hosts, veterinary surveillance helps to track the rate of Haemagglutination Inhibition (HI) antibody carriers and the appearance of antibody from fresh infection as an index of the spread of JE virus in animal host. Veterinary-based surveillance is conducted with the help of animal husbandry department. Sera sample from these animals is randomly collected for serology to ascertain transmission of JE virus. Sera sample from these animals is randomly collected for serology to ascertain transmission of JE virus.
  1. What are the Veterinary Research Institutes for screening for antibody carriers of pig, ducks and ardeid birds?
    i) National Institute of Virology (NIV), Pune.
    ii) Centre for Research in Medical Entomology (CRME), Madurai.

iii) VBRI (Veterinary Biological Research Institute), Shanthinagar, Hyderabad, Andhra Pradesh.

  1. iv) Kyasanoor Forest Disease Laboratory, Shimoga, Karnataka.
  2. v) Institute of Vector control and Zoonosis Hosur, Tamil NAdu.
  3. vi) Indian Veterinary Research Institute (IVRI), Izatnagar, Bareilly, U.P.243122.

vii) Diagnostic Research Laboratories, RWITC. Ltd. (Approved By Govt. of India), 6 Arjun Marg, Pune 411001, Maharashtra