Acute encephalitis syndrome

Acute encephalitis syndrome (AES) is a serious public health problem in India. It is characterized as acute-onset of fever and a change in mental status (mental confusion, disorientation, delirium, or coma) and/or new-onset of seizures in a person of any age at any time of the year. The disease most commonly affects children and young adults and can lead to considerable morbidity and mortality.

Viruses are the main causative agents in AES cases, although other sources such as bacteria, fungus, parasites, spirochetes, chemicals, toxins and noninfectious agents have also been reported over the past few decades.

Japanese encephalitis virus (JEV) is the major cause of AES in India (ranging from 5%-35%).Herpes simplex virus, Influenza A virus, West Nile virus, Chandipura virus, mumps, measles, dengue, Parvovirus B4, enteroviruses, Epstein-Barr virus and scrub typhus, S.pneumoniae are the other causes of AES in sporadic and outbreak form in India. Nipah virus, Zika virus are also found as causative agents for AES. The etiology in a large number of AES cases still remains unidentified.

AES due to JEV was clinically diagnosed in India for the first time in 1955 in the southern State of Madras, now Tamil Nadu. During 2018, 10485 AES cases and 632 deaths were reported from 17 states to the National Vector Borne Diseases Control Programme (NVBDCP)*in India, with a case fatality rate around 6 per cent. AES cases were reported mainly from Assam, Bihar, Jharkhand, Karnataka, Manipur, Meghalaya, Tripura, Tamil Nadu, Uttar Pradesh.



Sen. P.K. et al. Epidemiology of Acute Encephalitis Syndrome in India: Changing Paradigm and Implication for Control. J. Commun. Dis. 2014; 46(1): 4- 11. Accessed from-

Gosh. S. Acute Encephalitis Syndrome in India: The Changing Scenario. Annals of neurosciences. 2016 Sep; 23(3): 131–133. Accessed from

John.TJ. The syndrome of acute encephalitis in children in India: Need for new thinking. Indian Journal of Medical Research, 2017 Aug; 146(2): 158–161. Accessed from

Tiwari JK et al. Aetiological study of viruses causing acute encephalitis syndrome in North West India. Indian Journal of Medical Microbiology. 2017; 35:529-34. Accessed from -

Narain JP. Acute encephalitis in India: An unfolding tragedy. Indian J Med Res 2017 May; 145(5): 584–587. Accessed from

Kamble. S. et al. A clinico-epidemiological profile of acute encephalitis syndrome in children of Bellary, Karnataka, India. International Journal of Community Medicine and Public Health. 2016 Nov;3(11):2997-3002 DOI:



Acute Encephalitis Syndrome (AES) is a general description of the clinical presentation of a disease characterized by high fever altered consciousness mostly in children below 15 years of age.

Clinically, a case of AES is defined as a person of any age, at any time of year with the acute onset of fever and a change in mental status (including symptoms such as confusion, disorientation, coma, or inability to talk) AND/OR new onset of seizures (excluding simple febrile seizures). Other early clinical findings may include an increase in irritability, somnolence or abnormal behavior greater than that seen with usual febrile illness. 


Narain JP. Acute encephalitis in India : An unfolding tragedy. Indian J Med Res 2017 May; 145(5): 584–587, accessed from


Acute Encephalitis Syndrome (AES) has a very complex etiology. Causative agents of AES include a wide variety of viruses, bacteria, protozoa, fungi, and non- infectious agents. While Japanese encephalitis virus (JEV) is a leading cause of acute encephalitis syndrome in India (ranging from 5-35%), the etiology in a large number of cases however remains unidentified. In India during 2018, 15% of cases of AES were found positive for infection due to JEV.

Herpes simplex virus, Influenza A virus, West Nile virus, Chandipura virus, mumps, measles, dengue, Parvovirus B4, enteroviruses and scrub typhus, S.pneumoniae are the other causes of AES in sporadic and outbreak cases in India. In many cases, however, no etiological agent is determined. Tick-borne encephalitis virus – TBEV, Zika virus, Nipah virus are also found positive in AES cases.

Some are the zoonotic disease, that transmitted from animals to humans via mosquitoes (e.g. Japanese encephalitis virus, and West Nile virus) or ticks, (Tick-borne encephalitis virus), while for other flaviviruses humans are the natural hosts; these include dengue virus (DENV), and Zika virus (ZIKV).

Although AES cases other than JE continue to be reported throughout the year, there is an overall increase of total AES cases since the month of June, peak during July- August and decline in September- October.

The AES cases in Muzaffarpur, Bihar and adjoining litchi producing districts have been observed mostly during April to June particularly in children who are undernourished with a history of visiting litchi orchards. In 2014, a relationship between consumption of litchi and AES was postulated by National Centre for Disease Control, Delhi (along with Centre for Disease Control US) in acute encephalitis in children, in Muzaffarpur*.


Sen PK et al. Epidemiology of Acute Encephalitis Syndrome in India: Changing Paradigm and Implication for Control. J. Commun. Dis. 2014; 46(1): 4- 11. Accessed from-

Desai.A. Acute encephalitis syndrome of unknown etiology; The NIMHANS experience. International Journal of Infectious Diseases, April 2016 volume 45, Supplement 1, Page 25. Accessed

* Shrivastava .A. et al. Association of acute toxic encephalopathy with litchi consumption in an outbreak in Muzaffarpur, India 2014: a case control study. The Lancet, Volume 5, Issue 4, PE458-E466, April 01, 2017

Narain JP. Acute encephalitis in India : An unfolding tragedy. Indian J Med Res 2017 May; 145(5): 584–587. Accessed from



The National Vector Borne Disease Control Programme in India has set up country wide surveillance for AES through sentinel sites with a focus on detecting Japanese encephalitis (JEV). In the sentinel surveillance network, AES/JE is diagnosed by lgM Capture ELISA, and virus isolation is done in National Reference Laboratory.

Laboratory-Confirmed case is a suspected case with any one of the following markers:

  • Presence of lgM antibody in serum and/ or CSF to a specific virus including JE/Entero Virus or others
  • Four-fold difference in lgG antibody titre in paired sera
  • Virus isolation from brain tissue
  • Antigen detection by immunofluroscence
  • Nucleic acid detection by PCR


Management of AES is essentially symptomatic. First line of management should be started at grass root level. To reduce severe morbidity and mortality it is important to identify early warning signs and refer patient to higher health facility.

Danger Signs-

  • Fever with any one of the following:

Lethargy/ Unconsciousness/ Convulsions

Pre referral care-

  • Sponging with tap water if fever is present
  • Nothing to be given orally
  • Management of airway and breathing- Clear Airways
  • Patient’s position –
    • Turn the patient on the side to reduce risk of aspiration.
    • Keep the neck slightly extended and stabilize by placing cheek on one hand.
    • Bend one leg to stabilize the body position.
  • Referral to nearest first referral health facility.



The disease affects the central nervous system and can cause severe complications, seizures and even death. The Case Fatality Rate (CFR) of this disease is very high and those who survive may suffer from various degrees of neurological sequeale. (An estimated 25% of the affected children die, and among those who survive, about 30- 40% suffers from physical & mental impairment).



National Programme for Prevention and Control of Japanese Encephalitis(JE)/ Acute Encephalitis Syndrome (NPPCJA):

Considering the complexity of AES problem and to reduce morbidity, mortality and disability in children due to JE/AES, Government of India has developed a multi-pronged strategy with convergence of the concerned Ministries

  • Ministry of Health and Family Welfare:

o   Strengthening and expanding JE vaccination.

o   Strengthening of public health activities

o   Better clinical management of JE/AES Cases.

o   Physical medicine and rehabilitation (PMR)

o   Establishing of district counselling centres

o   Monitoring, supervision and coordination

o   Research-cum-intervention project

  • Ministry of Drinking Water and Sanitation for provision of safe water supply
  • Women and Child development for providing high quality nutrition to the vulnerable children
  • Ministry of Social Justice and Empowerment for establishing District Disability Rehabilitation Centers for disability management and rehabilitation.
  • Ministry of Housing and Urban Poverty Alleviation (HUPA) for ensuring the supply of safe water in slums and towns
  • Ministry of Human Resource (Department of School Education) to provide special facilities to disabled children for their education.

The major objectives of NPPCJA:

(i) to strengthen and expand JE vaccination in affected districts- In JE endemic areas, JE mass vaccination campaign is done using a single dose of live attenuated vaccine (SA-14-14-2) in children between 1- 15 years of age followed by routine immunization of children. Two doses of JE vaccination are provided under Universal immunization, first at 9-12 months along with measles and second with DPT booster at 16-24 months in JE endemic areas. JE vaccination of adult population is also started in selected districts of few endemic states.

(ii) to strengthen surveillance, vector control, case management and timely referral of serious and complicated cases;

(iii) to increase access to safe drinking water and proper sanitation facilities to the target population in affected rural and urban areas;

(iv) to estimate disability burden due to JE/AES, and to provide for adequate facilities for physical, medical, neurological and social rehabilitation.

(v) to improve nutritional status of children at risk of JE/AES;

(vi) to carry out intensified IEC/BCC activities regarding JE/AES.


  • PUBLISHED DATE : Mar 05, 2019
  • CREATED / VALIDATED BY : Dr. Aruna Rastogi
  • LAST UPDATED ON : Mar 05, 2019


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