Japanese encephalitis is a mosquito-borne viral disease that affects the brain. It is transmitted between pigs and birds by culicine mosquitoes. The virus can infect humans who are incidental dead-end hosts. Children under 15 are most at risk. There are vaccines available for humans and pigs that can help control the spread of the disease.

1. JAPANESE ENCEPHALITIS (BRAIN
FEVER)
Mrs. NAMITA BATRA GUIN
Associate Professor

2.  It is a mosquito borne encephalitis caused by group
B arbo-virus and transmitted by culicine
mosquitoes.
 It is a zoonotic disease.
 25 years ago, JE was known as endemic disease
in East Asia, especially Japan, China and Korea.
 Outbreaks of considerable magnitude has also
occurred in India.
 Vast majority of cases occur among children less
than 15 years of age.
 In India, recognition of JE was first made in 1955 in
Tamil Nadu.

3. EPIDEMIOLOGICAL FEATURES
 It has several extra human hosts e.g. animals and
birds.
 Basic cycles are: pig Mosquito Pig
 The ardeid Bird Mosquito Ardeid Bird
 The disease is transmitted to man by the infected
mosquitoes. Man is incidental dead-end host.
 Animal hosts- Pigs are major vertebrate hosts for JE
virus. Pigs are considered ‘amplifiers’ of the virus, as
they develop very high titers of the virus in their
blood.Cattles and buffaloes can also get infected.
 Birds- some species of bird such as pond herons, cattle
egrets and ducks are involved in the natural history of
JE virus.

4. MOSQUITO VECTORS
 Culicine mosquitoes along with some anophelines
are the vectors of the infection.
 These mosquitoes generally breed in irrigated rice
fields, shallow ditches and pools.
 Female mosquitoes get infected after feeding on
viraemic host and after 9-12 days of incubation
period they can transmit the virus to others.
 It is mostly a rural disease. It is considered the
seasonal disease as epidemics coincides with
monsoons and post monsoon season.

5. TRANSMISSION
 After mosquito bite disease appears in 5-16 days.
 The virus then invades the central nervous system and
causes disease.
 Although infection in human is incidental, the virus can
cause serious neurologic disease with high morbidity
and mortality.
 Infection during the first six months of pregnancy may
result in infection of the fetus an miscarriage.
 JE does NOT spread from child to child or from cattle
to humans because of the low and transient viremia.

7. JE IN MAN
 Incubation in man varies from 5-15 days.
 Not all individual bitten by the infected mosquitoes
develop the disease.
 The ratio of overt disease to inapparent infection
varies from 1:300 to 1:1000.
 Encephalitis cases due to JE show scattered
distribution.
 The incidence of JE disease is never an indication
of the risk at which the population is living in JE
endemic areas, because of in apparent infections.

8. JE IN MAN
 Prodromal stage: fever, headache and malaise.
Duration of this stage is usually 1-6 days.
 Acute encephalitis stage: fever is usually high 38-
40.7˚C . Prominent features are fever, nuchal
rigidity, focal CNS signs, convulsions and altered
sensorium progressing to coma in many cases.
 Late stage and sequelae: neurologic signs become
stationary or tend to improve. Convalescence may
be prolonged and residual neurological deficits may
not be uncommon.
 The average period between onset of illness and
death is about 9 days.

9. DIAGNOSIS
 ELISA – it detects the specific IgM in the
cerebrospinal fluid or in the blood of almost all the
patients within 7 days of the onset.
 The virus is rarely recovered in the tissue culture
from blood or CSF but may be found in the
encephalitic brain at autopsy.

10. CONTROL OF JE
 Vector control- fogging with ultra-low volume
insecticides. Indoor residual spray. Spraying should
cover the vegetations around houses.
 Villages within proximity of infected villages should be
kept under surveillance.
 Vaccination:- population at risk is recommended the
vaccine. JE live vaccine is safe for children and
effective for prevention from JE disease in JE endemic
areas.
 Two doses of 1 ml each (0.5 ml for children under the
age of 3 years) should be administered
subcutaneously at an interval of 4 weeks.
 A booster injection of 1 ml should be given after 1
year.

11. CONTROL OF JE
 For traveller’s visiting the endemic areas need the
vaccine administration at day 0, 7 and 28.
 Vaccine of swine is also important but it is difficult to
maintain vaccination coverage in the swine as their
population is renewed rapidly.
 Isolation of pigs is essential. The minimum distance for
pigsties is 5 kms from human habitations.
 Water management practice of Paddy cultivation: At
least one dry day every week and using neem
products as fertilizers will reduce the mosquito
population.