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Sir,

Japanese encephalitis (JE) is a mosquito borne viral disease that affects central nervous system and can cause severe complications and even death1. JE is a major seasonal health problem in many rural areas in India and other parts of Asia with 30-50,000 cases reported annually2,3. The onset of symptoms in JE infection is characterized by fever, headache, vomiting followed by nuchal rigidity, focal neurological signs, and convulsions and altered sensorium3. Case fatality rates vary from 20-40 per cent in children4. Nearly one half of the survivors have significant neurologic sequelae. In 1952, neutralizing antibodies to JE virus were found to exist in patients at several places in India like Nagpur district of Maharastra, Chingleput district of Tamil Nadu, Gujarat and Andhra Pradesh5. In Uttar Pradesh first outbreak occurred in 1978 in north eastern district2. A study from Lucknow suggested that disease was endemic in the north eastern districts of U.P. including Gorakhpur, Deoria, Ajamgarh, Basti, Gonda, Balia, Faizabad, and Lakhimpur KhM6-8.

This study was conducted in the Virology section of Post Graduate Department of Microbiology, King George’s Medical University, Lucknow during March and June 2005. A total of 57 consecutive cases suspected to have acute encephalitis were included in the study. Of these, 35 patients were from paediatric age group and 18 were adults. With the help of physician in-charge a detailed history was taken and physical examination was performed according to predesigned proforma. A careful record of patients’ progress in the hospital was maintained during his/her stay. Two blood samples (5 ml) were taken, one at the time of admission and another 8 days later. Paired sera could be collected only from 13 cases. Only single serum sample during acute phase of illness was collected from 44 patients. Thus, a total of 70 serum samples were subjected to haemagglutination inhibition (HI) test to established laboratory diagnosis of JE3. Blood was allowed to clot at room temperature and serum was separated by centrifugation. Kaolin treatment of the sera was done and samples were stored at -20γC. After collection of duck RBC and titration of the antigen, HI test was done for antibody titre. JE antigen control and RBC control were used to see for button and carpet formation. Haemagglutination titre was taken as highest dilution of serum which showed inhibition of agglutination. Four-fold increase in antibody titre was considered as positive HI test.

Of the 13 paired samples, seven were positive. Of these, in four samples diagnosis was made by fourfold or higher rise in HI antibody titre. In two samples, there was four-fold or more fall in HI antibody titre. One sample showed high titre throughout. Of the 57 cases, 16 (28.07%) were found to be positive for JEV antibodies (7 from paired sera and 9 from single serum). As this hospital is a State referral center for JE, most of the cases with history of acute onset of fever, headache, vomiting, altered sensorium with or without convulsions and other neurological deficits as case of acute encephalitis with strong suspicion of JE are referred to this hospital. Thus, we see a large number of JE cases.

Duration of illness also affects IgM antibody titre. As IgM appears immediately after infection in most cases, it does not present in high titre3. JE infection in its prodromal phase is of very nonspecific type, so it is possible that by the time patient reports and JE is suspected and sample is collected, IgM falls and becomes undetectable by ELISA. As IgG appears later and its concentration increases thereafter3, it is detectable by an appropriate test. Thakare et al* had suggested that MAC-ELISA negative samples should also be tested for JEV specific IgG subclass before ruling out the possibility of JE. So, HI can be used to make a diagnosis of JE either in avery early phase or in late phase of illness.

In the present study, maximum number of JE cases were in the age group less than 12 yr and the number decreased as the age increased. JEV mainly affected paediatric age group. In 1975, Chatterjee et al5 reported that mainly younger age groups were affected by JE. Later in 1982 Mathur et al2 showed that in epidemics of 1978 no age group was spared but more cases occurred in children below 10 yr of age. Outbreaks occurred in 1988 in UP also affected all age groups and maximum incidence was seen in children6.

Males are usually affected more than females. Of the 57 cases, 43 were males and 14 were females. Of the 16 JE positive cases, 10 were males. It may be due to the reason of males sleeping outside the houses with bare body.

Mosquito population increases after rains and there is an increase in the incidence of JE cases7. JE is mainly thought to be a disease of rural area8 but in the present study (36.36%) cases were reported from urban area, 63.63 per cent from rural area.

Most of the cases presented with fever and altered sensorium. In India, Reuben et aP reported the range of case fatality from 10-60 per cent and Kumar et aP have given a range of 20-50 per cent. In our study, case fatality was 12.5 per cent of patients. The low case fatality may be because our study population was small and some of the cases could not be followed up, other reasons could be improved hospital facilities and symptomatic care.

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