Japanese Encephalitis (JE): Epidemiological perspective, History, Importance and vaccination in Nepal

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 8^th 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.