JAPANESE
B
ENCEPHALITIS
Dr.T.V.Rao MD

Japanese B virus Infection
Infection is caused by a flavivirus, a single
stranded RNA virus. It is transmitted by
the bite of the Culex tritaeniorhynchus
mosquito. The virus multiplies at the site
of the bite and in regional lymph nodes
before viraemia develops. Viraemia can
lead to inflammatory changes in the heart,
lungs, liver, and reticuloendothelial
system.

A Flavivirus
Japanese encephalitis ( previously

known as Japanese B encephalitis is a
disease caused by the mosquito-borne
Japanese encephalitis virus. The Japanese
encephalitis virus is a virus from the
family Flaviviridae. Domestic pigs and
wild birds are reservoirs of the virus;
transmission to humans may

A leading cause of viral
encepalitis
Japanese encephalitis is the leading cause

of viral encephalitis in Asia, with 30,000–
50,000 cases reported annually. Case-
fatality rates range from 0.3% to 60% and
depends on the population and on age.

A Vector born- Arboviral
Infection
Culex tritaeniorhynchus

a rural Mosquito that
breeds in rice fields, is
the principle vector.
In India in 1955 the virus
were isolated from Culex
vishnui mosquitoes in
Vellore region in Tamil
Nadu

INCIDENCE
Leading cause of viral encephalitis in Asia

with 30-50,000 cases reported annually
 Fewer than 1 case/year in U.S. civilians
and military personnel travelling to and
living in Asia
 Rare outbreaks in U.S. territories in
Western Pacific

Distribution of Japanese
Encephalitis in Asia, 1970-1998

Japanese B Encepalitis
Virus
The causative agent

Japanese encephalitis
virus is an enveloped
virus of the genus
Flavivirius; Positive sense
single stranded RNA
genome is packaged in
the capsid, formed by the
capsid protein. The outer
envelope is formed by
envelope (E) protein and
is the protective antigen.

Genus - Flavivirus
Japanese B encepalitis

virus is
Spherical, 40 – 60 nm in
diameter
Contain a positive sense
Single stranded RNA, 11
kb in size
RNA genome is infectious
Several viruses in this
group are related.

Structure of Virus
The outer envelope is formed by envelope (E)

protein and is the protective antigen. It aids in
entry of the virus to the inside of the cell. The
genome also encodes several non-structural
proteins also
(NS1,NS2a,NS2b,NS3,N4a,NS4b,NS5). NS1 is
produced as secretary form also. NS3 is a
putative helicase, and NS5 is the viral
polymerase.

Cycle of Events in Japanese B
encepalitis

Pass through two prominent
Hosts
Herons act as

reservoir hosts and
pigs as amplifier
hosts.
Human infection is a

tangential ‘dead end’
and infections are
spread when the
infected mosquitoes
reach high density.

Clinical Manifestations
The incubation period is 6 to 16 days.

There is a prodrome of fever, headache, nausea,

diarrhoea, vomiting, and myalgia, which may
last for several days.
This may be followed by a spectrum of

neurological disease ranging from mild
confusion, to agitation, to overt coma.
Two thirds of patients have seizures. It is more

common in children, while headache and
meningism are more common in adults.

Can lead to Neurological
damage
Tremor or other involuntary movements

are common.
 Mutism has been described as a
presenting symptom. So has a syndrome
of acute flaccid paralysis.
 Fever resolves by the second week, and
choreoathetosis or extra pyramidal
symptoms develop as the other
neurological symptoms disappear.

Diagnosis of Japanese B
Encephalitis
The isolation of virus

from Blood, CSF, or
tissues.
Detection of Arboviral

specific RNA in
blood,CSF, or Tissue
However very few

reference laboratories can
perform the isolation in
view of the biosafety
considerations

Serology by ELISA
IgM capture enzyme-linked immunoassay

(ELISA) of serum or CSF is the standard
diagnostic test. Sensitivity is nearly 100% when
both serum and CSF are tested. False-negatives
may result if the samples are tested too early, as
in the first week of illness.
New IgM dot enzyme immunoassays for CSF and

serum are portable and simple tests that can be
used in the field. Compared with ELISA as the
gold standard, the sensitivity and specificity are
around 98 and 99% respectively.

False Positive Tests
There is some cross-reactivity with other

flavivirus and from Japanese encephalitis
and yellow fever vaccinations.

Arboviral Specific RNA
detection
Viral RNA is extracted

from serum or from
suspected tissues of the
patients or mosquito
homogenates.
The product is amplified

by RTPCR and the
products analyzed by
restriction digestion and
determined by nucleotide
sequence of PCR product.
The identified sequence is

compared with nucleotide
sequence found in Gene
bank or other data bases

Preventive measures
Preventive measures include mosquito control

and locating piggeries away from human
dwellings
A formalin inactivated mouse brain vaccine

using the Nakayama strain has been employed
in human immunization in Japan – Two doses at
two week’s interval followed by a booster 6 – 12
months later constitute a full course.
However the immunity was short lived


Later vaccines
A live attenuated vaccine has been

developed in China from JE strain SA 14-
14-2, passed through weanling mice
 The vaccine is produced in primary baby
hamster kidney cells.
 Administered in two doses, one year
apart, the vaccine has been reportedly
effective in preventing clinical disease

Basics on Vaccinations
Vaccine: formaldehyde-inactivated, purified from

mouse brain
minimum age: 1 year - safety/efficacy in infants

uncertain
primary course: day 1, day 7-14 and day 28 (3

doses)
dose: adults & children over 3 years 1ml

s.c./i.m.; children under 3 years 0.5ml s.c./i.m.
booster interval: 2 years


Indications for Vaccination
for long-stay travellers, especially children,

to endemic areas of India, Nepal, Bhutan,
China and SE Asia (May-Sept in SE Asia,
July-Dec in Nepal or India)

Slaughter of PIGS
During major epidemics, slaughter of pigs

has been employed as a measure of
containment.

RESEARCH PRIORITIES
Facilitate implementation of attenuated vaccine

in unvaccinated populations in endemic areas
Develop improved vaccines

Identify risk factors for progression to

symptomatic encephalitis and viral persistence
Describe clinical features of JE in AIDS and

determine its potential as an opportunistic
infection

Created for Medical and
Paramedical students in
Developing World
Dr.T.V.Rao MD
Email
doctortvrao@gmail.com