Japanese
Encephalitis (JE): Epidemiological perspective, History, Importance and
vaccination in Nepal
Japanese Encephalitis (JE) carries high public
health importance because of its epidemic potential and high case fatality
rate. Though less than 1% of people infected
with the JE virus develop clinical disease, approximately 20–30% of cases are
fatal and 30–50% of survivors have long-term neurological sequelae.
Therefore, JE is considered a disease with
significant public health and economic burdens.
It is a mosquito borne zoonotic disease (Note: A zoonotic disease is a disease that
can be spread between animals and humans)
Epidemiological Perspectives of Japanese Encephalitis
Causative organism: arbovirus (Flavivirus)
Vector: It is a Mosquito borne, Culex tritaeniorhynchus is common in transmitting JE virus in Nepal.
Incidental host: Human (Human have low viral
load, usually not sufficient for transmission from Human to Human)
Amplifying host: Pig, migratory birds
(amplifying host: the host which provides environment suitable for
proliferation, being an important source of infection for
vectors in vector-borne diseases.)
Environment: It is endemic in rural areas,
especially where rice growing and pig farming coexist, and epidemics occur in
rural, sub-urban and occasionally in urban areas.
Season: It is a seasonal disease. Highest
transmission rates occur during and just after wet seasons, when mosquitoes are
most active, but seasonal patterns vary both within individual countries and
from year to year. This disease is not transmitted from person to person.
History of Japanese Encephalitis
Outbreaks were recorded in Japan as early as
1871; the first major epidemic in Japan was described in 1924 and involved 6000
cases. However, the virus was isolated
for the first time in the world from a post-mortem human brain in Japan in 1933.
The first inactivated mouse-brain derived vaccines were produced in the same
decade of 1930s.
JE spread throughout Asia but national immunization
campaigns and urban development in the 1960s led to the near-elimination of JE
in Japan, Korea, Singapore and Taiwan. However, JE remains endemic in much of
the rest of Asia.
In Nepal, JE occurred first time during
the year 1978 in Rupandehi district then in Sunsari, Morang and has since
become endemic in all districts of Terai and Inner Terai.
Why is Nepal at risk of Japanese Encephalitis?
Culex mosquito is endemic
High-risk districts where JE is endemic
The mosquitoes that transmit this
disease breed in and around dirty, stagnant water and in areas where the pigs
are farmed.
Why does it need attention?
High fatality rate
No definite treatment
Epidemic potential as the mosquito bite can
spread to many people
Neurological sequelae
High economic burden
Climate change leading to spread and
proliferation of vector in low risk area
Japanese Encephalitis Vaccination in Nepal:
JE
surveillance in Nepal was started in 2004. The vaccination campaign against JE
was introdueced in the year 1999 for the first time in Nepal. Following vaccination
campaigns against JE began in 2006 using live attenuated SA-14-14-2 JE vaccine
in high-risk districts of Terai. Japansese
vaccination campaigns in Nepal have been carried out in phase wise manner since
2006 for the people all above one year of age.
As of
2010, the campaigns were completed in 23 districts. All persons above one year
of age were vaccinated in 12 districts and persons above one year of age and
below fifteen years of age were vaccinated in 11 districts.
JE
vaccine was introduced into the routine immunization program in 2009 in the
post JE campaign districts. All
the children of endemic region should be vaccinated at the age of 12-23 months
in routine immunization program of Nepal. The coverage ranges widely from
8-73%.
Previously
JE was limited to Terai, inner Terai and Kathmandu region but cases have been
reported from hilly and mountainous region as well so JE campaign have been
scaled up to other districts. This year JE vaccination campaign is being run
from 8th to 13 th May, 2016 in 44 new districts of Nepal and 3 old
districts.
JE vaccine: It is a freeze dried vaccine and should be reconstituted with its solution.
Amount: 0.5ml
Route of administration: subcutaneously
Storage: 2-8 degree centigrade
This vaccine should be used immediately after reconstitution.
Sources:
1. Campbell GL, Hills
SL, Fischer M, Jacobson JA, Hoke CH, et al. (2011) Estimated global incidence
of Japanese encephalitis: a systematic review. Bulletin of the World Health
Organization 89: 766–774. doi: 10.2471/blt.10.085233
2. http://www.nepalihealth.com/2016/05/07/5426/
3. Shyam Raj Upreti, Kristen B. Janusz, W.
William Schluter, Ram Padarath Bichha, Geeta Shakya, Brad J. Biggerstaff, Murari
Man Shrestha, Tika Ram Sedai, Marc Fischer, Robert V. Gibbons, Sanjaya K.
Shrestha, and Susan L. Hills. Estimation
of the Impact of a Japanese Encephalitis Immunization Program with Live,
Attenuated SA 14-14-2 Vaccine in Nepal. Am J Trop Med Hyg. 2013 Mar 6; 88(3):
464–468.
