Source: http://timesofindia.indiatimes.com/n...ow/4946281.cms

In Assam, Japanese Encephalitis records an age shift
Kounteya Sinha, TNN 29 August 2009, 12:35am IST

NEW DELHI: It's like a virus that has undergone a complete
personality change.

India has started to record a complete age shift in those infected by the Japanese Encephalitis -- the vector borne viral killer. Till now, scientists believed that in most JE endemic states, the virus infected only the under-15 age group. However, a present outbreak in Assam has the Union health ministry perplexed. Almost 74% of the cases reported till now in the state have been in the above-15 age group.

Till now this year, Assam has recorded 164 cases of Acute Encephalitis Syndrome (AES) -- a severe neurological condition associated with significant morbidity and mortality.

Of these, 91 have now been lab confirmed to be caused by JE. AED has also killed 78 people since April.

"Around 67 of these 91 JE cases (74%), are above 15 years of age with the eldest in this affected group being a 58-year-old. This is highly unusual and we have no idea why it has happened. This is a new trend," JE expert from international NGO Path Dr Pritu Dhalaria told TOI.

Till now, India vaccinated only the under-15 age group with the JE vaccine. However, this age shift trend has now made the Assan government decide to vaccinate the entire population in the seven worst affected districts -- Sibsagar, Dibrugarh, Tinsukia, Jorhat, Kolaghat, Dimaji and Lakhimpur.

The government has estimated that 8 million doses of the vaccine will be required to vaccinate the entire population in these districts. The vaccine and operational hurdles will in total cost the state Rs 15 crore.

"The state had just one query -- will the vaccine be safe for adults? And it is. The vaccine will have to be given in the same dose as for kids and is as effective on adults. Nepal used the same strategy in four of its worst affected districts in 2007," Dr Dhalaria said.

The vaccine will have to be imported from China which Path is facilitating. It will, however, take six months for the vaccines to arrive. India has been completely dependent on China for its supply of the SA14-14-2 anti-JE vaccine from China National Biotech Group's Chengdu Institute. India first imported the Chinese vaccine in February 2006 after a sudden outbreak of JE the previous year killed over 1,800 people.

The single shot vaccine made from a live attenuated virus (live cells like bacteria grown in laboratory, infected with the JE virus and then purified to make the vaccine) has 90% efficacy and costs around Rs 10 per dose.

According to vector experts at NICD, the age shift in Assam could have happened because the adults didn't have immunity against the virus.

"In known endemic belts of Karnataka, Tamil Nadu, Andhra Pradesh and Uttar Pradesh, transmission usually occurred in children because adults have some immunity against it due to repeated exposure. Maybe the virus is spreading to new uninfected areas of Assam where lack of an earlier outbreak has made even adults vulnerable," officials said.

JE affects the human central nervous system. Globally up to 50,000 cases of JE are reported every year, one-third of its survivors suffering from permanent neurological damage.

The JE virus is transmitted to humans via the bite of an infected mosquito. The mosquitoes usually get infected when feeding on domestic pigs that already carry the virus. The Culex Tritaeniorhynchus group of mosquito is the primary transmitter of JE to humans.

If a mosquito bites an infected animal and then bites a human, the person can become infected with the JE virus. After a person is bitten, the JE virus invades the central nervous system, damaging the brain and spinal cord. Immunization is the most effective approach to prevent the disease.