Japnese Enchephalitis Virus is spread by Culex Mosquitoe.

1. Japanese encephalitis virus
Dr.Akshay Minhas
Tutor , Department of Community Medicine
SLBSGMC Mandi, Himachal Pradesh
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3. Key facts
Japanese encephalitis virus (JEV) is a flavivirus related
to dengue, yellow fever and West Nile viruses, and is
spread by mosquitoes.
JEV is the main cause of viral encephalitis in many
countries of Asia with an estimated 68 000 clinical cases
every year.
Although symptomatic Japanese encephalitis (JE) is
rare, the case- fatality rate among those with
encephalitis can be as high as 30%. Permanent
neurologic or psychiatric sequelae can occur in 30%–
50% of those with encephalitis.
24 countries in the WHO South-East Asia and Western
Pacific regions have endemic JEV transmission,
exposing more than 3 billion people to risks of infection.
There is no cure for the disease. Treatment is focused
on relieving severe clinical signs and supporting the
patient to overcome the infection.
Safe and effective vaccines are available to prevent JE.

4. Introduction
Japanese encephalitis virus JEV is the most cause of viral
encephalitis in Asia.
It is a mosquito-borne flavivirus, and belongs to the same genus as
dengue, yellow fever and West Nile viruses.
The first case of Japanese encephalitis viral disease (JE) was
documented in 1871 in Japan.
The annual incidence of clinical disease varies both across and within
endemic countries, ranging from <1 to >10 per 100 000 population or
higher during outbreaks.
A literature review estimates nearly 68 000 clinical cases of JE
globally each year, with approximately 13 600 to
20 400 deaths.
JE primarily affects children.
Most adults in endemic countries have natural immunity after
childhood infection, but individuals of any age may be affected.

5. Ecology and Epidemiology
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6. Ecology and epidemiology
24 countries in the WHO South-East Asia and Western Pacific regions
have JEV transmission risk, which includes more than 3 billion people.
JEV is transmitted to humans through bites from infected mosquitoes
of the Culex species (mainly Culex tritaeniorhynchus).
The virus is transmitted in an enzootic cycle among mosquitoes and
amplifying vertebrate hosts, chiefly ardeid (wading) birds and domestic pigs .
Humans are incidental hosts as transmission from human-to-mosquito is not
possible because of low levels of viraemia found in humans, making humans
dead-end hosts.

7. Culex mosquitoes, primarily C. tritaeniorhynchus, are the
principal vectors.
Both male and female mosquitoes feed on plant fluids and
nectar.
However, the female typically requires a blood meal from
a warm-blooded animal before a viable batch of eggs can
be laid, and only the female is capable of sucking blood
and it bite mainly in night.

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9. The geographic spread of JE may be related to increasing international trade and
travel, and global warming could permit overwintering in more temperate regions.
JEV is transmitted seasonally in most areas of Asia, but there are, in broad terms, two
epidemiological patterns.
In northern (temperate) regions, JEV is transmitted during the summer months, around
May to September.
In southern (subtropical and tropical) regions, the virus is largely endemic, with
sporadic outbreaks throughout the year, peaking at the start of the rainy season.
Across affected Asia-Pacific countries, approximately 67 900 clinical cases of
JE are documented per year; of these, an estimated 13 600 to 20 400 deaths
occur annually .

10. Five different genotypes have been identified with genotype
3 having historically been the most common; however,
genotype 1 is becoming a more common circulating
genotype.
The major JEV genotypes have varying overlap in
geographical distribution but all belong to the same serotype
and are similar in terms of virulence and host preference .
Incidence of disease can fluctuate as JE transmission varies
from year to year.
Historically thought to be a childhood disease, the annual
incidence of JE in those younger than 15 years of age is an

11. The highest mortality rate from JE is in Uttar Pradesh where children’s
deaths in Gorakhpur recently sent shock waves all over the country.
These deaths were primarily attributed to JE aggravated by poor healthcare
facilities.
Since 2010, India has seen 10,893 JE cases and 1,756 deaths, a mortality
rate of 17 per cent.
Due to a large variation across regions, incidence in those younger than 15
years of age may be as high as an estimated 12.6/100 000 in some high
incidence areas in China and the Democratic People’s Republic of Korea.

12. In some countries even without vaccination programmes,
such as Bangladesh, a substantial proportion of cases are
in those older than 15 years of age .
In Thailand, 69% of individuals 20–24 years had
protective levels of neutralising antibody, and by 40
years of age, approximately 90% of the population had
protective levels of antibody titers.
Among a sample of unvaccinated 12–18 year- olds in the
Philippines, the seroprevalence rate was just 44%.

13. These data suggest an important proportion of adults are
still susceptible.
How severity differs by age group is not well understood,
in part because of the lack of follow up of many cases.
The age-specific incidence may be considered when
designing immunisation programmes, and some
countries, such as Nepal and India , have chosen to
conduct campaigns in which all individuals over one year

14. Who is at risk?
• Residents of rural areas in endemic locations
• Those who are deployed to work on those
areas
• Usually its not spread in Urban areas but due

15. Signs and symptoms
Incubation period:
– Normally 5 to 15 days
JEV infections are mild (fever and headache) or without
apparent symptoms, but approximately 1 in 250 infections
results in severe clinical illness.

16. Most infections are asymptomatic;
however, clinical cases can rapidly
progress to severe symptoms with an
estimated 30% of survivors experience
long-term neurologic abnormalities and
serious disabilities.
Of all clinical cases, 20–30% die, and
the risk of severe disease and death in
children younger than 10 years is even
higher.

17. Diagnosis
Individuals who live in or have travelled to a JE-endemic area and
experience encephalitis are considered a suspected JE case.
To confirm JEV infection and to rule out other causes of encephalitis
requires a laboratory testing of serum or, preferentially, cerebrospinal
fluid.
Surveillance of the disease is mostly syndromic for acute encephalitis.
Confirmatory laboratory testing is often conducted in dedicated
sentinel sites, and efforts are undertaken to expand laboratory- based
surveillance.
Case-based surveillance is established in countries that effectively
control JE through vaccination.

18. Treatment & Prevention and control
There is no antiviral treatment for patients with JE.
Treatment is supportive to relieve symptoms and stabilize the
patient.
Safe and effective JE vaccines are available to prevent disease.
WHO recommends having strong JE prevention and control
activities, including JE immunization in all regions where the disease
is a recognized public health priority, along with strengthening
surveillance and reporting mechanisms.
Even if the number of JE- confirmed cases is low, vaccination
should be considered where there is a suitable environment for JE
virus transmission.
There is little evidence to support a reduction in JE disease burden
from interventions other than the vaccination of humans.

19. There are 4 main types of JE vaccines currently in use:
inactivated mouse brain- derived vaccines, inactivated
Vero cell- derived vaccines, live attenuated vaccines,
and live recombinant vaccines.
Over the past years, the live attenuated SA14-14-2
vaccine manufactured in China has become the most
widely used vaccine in endemic countries, and it was
prequalified by WHO in October 2013.
Cell-culture based inactivated vaccines and the live
recombinant vaccine based on the yellow fever vaccine
strain have also been licensed and WHO-prequalified.

20. In November 2013, GAVI opened a funding window to
support JE vaccination campaigns in eligible countries.
All travellers to Japanese encephalitis- endemic areas
should take precautions to avoid mosquito bites to
reduce the risk for JE.
Personal preventive measures include the use of
repellents, long-sleeved clothes, coils and vaporizers.
Travellers spending extensive time in JE endemic areas
are recommended to get vaccinated.

21. JE Vaccine in India
JE Vaccination :113 JE endemic districts have completed the JE mass
vaccination and are implementing JE under routine vaccination.
2nd dose of JE is also introduced in RI in JE endemic states since April,
2013
National Vector borne Disease control Program Division (NVBDCP) has
identified 62 new JE endemic Districts.
JE campaign in these new districts targeting children between 1-15 years
of age is planned in a phased manner.
Uttar Pradesh, West Bengal, Karnataka, Assam and Bihar.

22. What you can do?
Environmental Control
Environment manipulation : elimination of breeding spaces, filling and drainage operation, carefully
planned water management, provision of piped water supply, proper disposal of refuse and other waste,
intensive cleaning in and around houses.
Personal Protection against mosquito bite : Mosquito net, screening , repellents .
Chemical Control
Wide range of insecticides are available but due to resistance and environmental pollution they are not effective .
Newer generations insecticides like methoxychlor, abate and dursban are recommended as they are biodegradable .
Biological Control
To minimise environmental pollution with toxic chemical biological control like fish(Gambusia), bacteria, fungi ,
protozoa and viruses are under study. Although these may pose a direct hazard to the health of man himself.

23. Control of piggeries
Integrated Approach
Culex. quinquefasciatus, best controlled by improving sanitation
and installing modern sewage systems, but often this is not
feasible and integrated approach to be implemented .

24. Disease outbreaks
Major outbreaks of JE occur every 2-15 years.
JE transmission intensifies during the rainy
season, during which vector populations increase.
However, there has not yet been evidence of
increased JEV transmission following major
floods or tsunamis.
The spread of JEV in new areas has been
correlated with agricultural development and
intensive rice cultivation supported by irrigation
programmes.
“Herd immunity” cannot be attained through
vaccination due to the zoonotic nature of the virus
— it remains in the environment.

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Eggs of culex mosquito in water