# Acute Encephalitis Syndrome in India

> Acute encephalitis syndrome in India for NEET-PG Medicine, covering the case definition, Japanese encephalitis, scrub typhus, enterovirus and litchi-associated causes.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/acute-encephalitis-syndrome-in-india
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Harrison's Principles of Internal Medicine; Nelson Textbook of Pediatrics; IDSP Acute Encephalitis Syndrome surveillance guidelines
- How to cite: "Acute Encephalitis Syndrome in India", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/acute-encephalitis-syndrome-in-india

## Direct answer

Acute encephalitis syndrome is a clinical and surveillance term for acute fever with altered sensorium or new seizures, used before the cause is known. Under the Indian surveillance definition it applies to a person of any age, though most cases are children, and Japanese encephalitis, scrub typhus, enterovirus and litchi-associated hypoglycaemia are among its recognised causes. Initial management is supportive, with immediate glucose correction, anticonvulsants and empirical antiviral cover while the aetiology is sought.

## What you must remember

- **Case definition:** acute fever with altered mental status and/or new-onset seizures in a person of any age (most cases are children), with simple febrile seizures excluded.
- **Japanese encephalitis:** a flavivirus transmitted by Culex mosquitoes, with pigs as amplifying hosts, and prevented by vaccination.
- **Scrub typhus:** Orientia tsutsugamushi transmitted by trombiculid mite larvae, often with an eschar, and treated with doxycycline.
- **Enterovirus:** a recognised cause of encephalitis in children, identified by viral testing in outbreaks.
- **Litchi-associated illness:** hypoglycaemia in children in Muzaffarpur, Bihar, linked with unripe litchi eaten on an empty stomach.
- **Chandipura virus:** a sandfly-transmitted cause of outbreaks in Gujarat.
- **Glucose first:** hypoglycaemia is an early, reversible threat and is corrected before any other step.
- **Herpes simplex:** treatable with intravenous acyclovir, which is started empirically while it cannot be excluded.

## Working up the common Indian causes

Acute encephalitis syndrome is worked up in parallel, because the causes differ in treatment and in prevention. The table lists the Indian causes that examiners most often expect.

| Cause | Key feature | Specific management |
|---|---|---|
| Japanese encephalitis | Culex-transmitted, with monsoon-season peaks | Supportive; vaccination for prevention |
| Scrub typhus | Eschar or mite exposure, rickettsial illness | Doxycycline |
| Litchi-associated | Hypoglycaemia after unripe fruit | Immediate glucose correction |
| Chandipura virus | Sandfly-transmitted outbreaks in Gujarat | Supportive care |
| Herpes simplex | Focal features, temporal lobe involvement | Intravenous acyclovir |

Glucose is checked and corrected before anything else, since hypoglycaemia is an early, reversible threat. Empirical acyclovir is started while herpes simplex cannot be excluded, because that encephalitis is treatable and fatal if missed. Doxycycline is added when scrub typhus is suspected, and vaccination is the main prevention for Japanese encephalitis.

## Where the exam tries to catch you

Examiners test whether you treat acute encephalitis syndrome as a syndrome with several causes rather than a single disease.

- **Trap:** labelling every febrile child with a seizure as Japanese encephalitis — **Correct:** the syndrome has several causes, so the aetiology must be sought before naming one.
- **Trap:** withholding empirical acyclovir until virology returns — **Correct:** herpes encephalitis is treatable, so acyclovir is started while the work-up continues.
- **Trap:** ignoring hypoglycaemia in a child with litchi exposure — **Correct:** glucose correction is the immediate and most effective step in that setting.

## Frequently asked questions

### What is the case definition of acute encephalitis syndrome used in India?

The surveillance case definition of acute encephalitis syndrome in India is acute onset of fever in a person of any age, at any time of year, with a change in mental status and/or new-onset seizures. Simple febrile seizures do not meet the definition, although most cases are children.

### Which mosquito transmits Japanese encephalitis and how is it prevented?

Japanese encephalitis is transmitted by Culex mosquitoes, with pigs and wading birds acting as amplifying hosts. Prevention relies on vaccination of children in endemic areas and on mosquito control, because there is no specific antiviral treatment.

### Why is hypoglycaemia checked in acute encephalitis syndrome in Bihar?

Hypoglycaemia is checked in acute encephalitis syndrome because outbreaks in Muzaffarpur, Bihar, have been linked with unripe litchi eaten on an empty stomach. Blood glucose must be corrected immediately, since this is a reversible and urgent cause of the illness.

### What is the specific treatment for scrub typhus encephalitis?

Scrub typhus encephalitis is treated with doxycycline, which targets Orientia tsutsugamushi, and azithromycin is an alternative in some regimens. Treatment should begin on clinical suspicion, especially when an eschar or mite exposure is reported.

### Why is empirical acyclovir started in acute encephalitis syndrome?

Empirical acyclovir is started because herpes simplex encephalitis is treatable and carries high mortality if missed. It is given intravenously while the cause is sought, and it is stopped if herpes simplex is excluded.