Japanese encephalitis (JE), previously known as Japanese B encephalitis, recently become one of the most dreaded ailments as year after year it has been taking a heavy toll of lives all over India, particularly the Northeast. Having no specific curative treatment to date, JE is a viral infection of the body, particularly affecting the brain and the nervous system. The virus belongs to the group Arbor. The virus is called Arthropod Borne Virus (Arthropod borne virus — Arbor virus) as they are transmitted by insects that have jointed foot. It is mainly transmitted to human beings from animals and birds by culex mosquitoes.

The culex is a common mosquito, and unlike anopheline mosquitoes, both male and female, can carry and transmit the virus whereas in the case of malaria it is only the female Anopheline variety which can carry and transmit malaria parasite. Malaria is a parasitic disease and not a viral disease.

JE is endemic in southeast Asia and far eastern countries and sometimes assumes a pandemic proportion by affecting large number of people in different countries. Animals like domestic pig and birds are possible sources of infection and the transmitting insects get infected during its blood meal. The viruses do not damage the tissues of the insect. They transmit the infection when they take their next meal.

The virus is widespread in the Pacific islands from Japan to Guam and also in The Philippines, Malaysia, Borneo and Australia. In the endemic areas laboratory serological tests show high incidence of subclinical infection i.e. people get infected without developing overt clinical symptoms.

Children are particularly vulnerable to this infection. Symptoms include high fever, headache, vomiting and convulsion. Severe cases gradually progress to clouding of senses and consciousness progressing to coma. There may be various nerve paralysis. Acute illness may continue for 2 to 4 weeks. Mortality varies from 15 to 40 per cent.

For its prevention, elimination of breeding places of mosquitoes is an urgent need. Vaccines for JE were first introduced in Japan in 1930. Subsequently, vaccines have been developed but the high cost is a deterrent. However, the adverse effect of vaccination are pain and redness at the injection site. There may be allergic rash. Worldwide research is going on. One silver lining, however, is that infection with JE virus gives lifelong immunity.

Dr Niraj Ananda Bharali