A retrospective study on the seasonal occurrence of Japanese Encephalitis cases in Uttar Pradesh

INTRODUCTION

Japanese encephalitis (JE) is caused by a Group B Arbovirus (Flavivirus). Culicine mosquitoes are the main vector of this disease. Its zoonotic disease infecting mainly animals but can affects humans also. Majority of the cases occur among children <15 years of age. Transmission occurs in agricultural areas, where flooding irrigation is practiced.¹

Japanese encephalitis is so called because for the first time severe epidemic of encephalitis occurred in Japan during 1924 and then epidemics occurred almost annually thereafter till 1970. Since then it has been declining in Japan but started in almost all SE Asian countries. JE is common in SE Asian countries including India and rare in other parts of the world. Globally about 43,000 cases of JE occur each year with 11,000 deaths and 9000 disabled. Fatality rate ranges from 20–40%.² Nearly 3 billion people or close to half the global population live in Japanese encephalitis endemic regions.³

First case was reported in 1955 in Tamil Nadu and the disease was restricted to South India. Spread started to North India in 1978 from where extensive and recurrent outbreaks of JE have been reported ever since.4 In India, State of UP contributed a large portion of JE cases to the country.⁵

JE is of particular interest as it has a high morbidity and mortality affecting both pediatric and adult age group. Neurologic or psychiatric components observed in 30–50% of survivors.⁶ Neurological sequalae is the most dreaded damage caused by JE. Understanding of seasonal occurrence of JE cases in Uttar Pradesh is extremely important to manage the encephalitis cases individually and to contain the epidemic in the community.

METHODS

The present retrospective study was conducted in the state of Uttar Pradesh, which is the most populous state of the country. It consist of 75 districts that has been clustered into 18 administrative divisions.⁶ For the study, we used secondary data, shared by Communicable Disease wing of Swasthya Bhawan, Lucknow, Uttar Pradesh (U.P), a government institution, for the analysis and prior permission was taken for the same.

We used data for the study during the past 7 years (2010–2016). To assess the seasonal occurrence of the JE cases, the year can be broadly divided into three seasons: summer (March to May), monsoon (June to September) and winter (October to February).⁷ Data was arranged and analyzed for the following variables like month-wise case occurrence, annual incidence and seasonal occurrence. Analysis has been done using Microsoft Excel.

RESULTS

In the present study, we used data of JE cases from 2010 to 2016 for analysis. In the last 7 years (2010-2016), total cases of JE in Uttar Pradesh were 1322 (Table 1). On classifying the JE cases according to their month of occurrence, majority of the cases were found in months of September (31.77%) followed by October (24.74%) and August (24.05%) (Table 1).

On arranging the JE cases according to the season, it was observed that maximum cases (63.92%) occurred in monsoon (rainy) season starting from the month of June to September followed by winter season (34.80%) (Figure 1). Cases were at peak in rainy season as compare to summer months. Very few cases were seen in summer season.

On considering the yearly occurrence of the cases from 2010 to 2016, it was also observed that there was a annual fluctuation in the occurrence of JE cases with overall decreasing trend with an exception of year 2016 (Figure 2). Out of total cases in the last 7 years, maximum percentage of cases were seen in 2010 (31.54%) and minimum in 2014 (7.64%) (Figure 2).

Among the U.P. districts, most cases were seen in Gorakhpur (25.18%) followed by Kushinagar (24.35%) and Deoria (13.58%). In geographical distribution of JE cases majority of the cases were found in the eastern part of Uttar Pradesh.

DISCUSSION

In the present study, total cases of JE in Uttar Pradesh were 1322 in the last 7 years (2010-2016). On classifying the JE cases according to their month of occurrence, majority of the cases were found in months of September (31.77%). Similar findings have been reported by other authors while in study conducted by Sarkar et al at Assam, peak of JE incidence occurred in the month of July.^6-8 On arranging the JE cases according to the season, it was observed that maximum cases (63.92%) were observed in rainy season starting from the month of June to September which coincides with paddy cultivation and the period of peak mosquito density. This finding is similar to the observations made by Kanojia et al and Sarkar et al.^7,8

On considering the yearly occurrence of the cases from 2010 to 2016, it was also observed that there was an overall decreasing trend in the yearly occurrence of the case with some fluctuations. These findings are consistent with other studies by different researcher.⁶ This may be because of the improvement in the health care services in the state.

In our study, majority of the cases were found in Gorakhpur (25.18%) district of Uttar Pradesh (U.P) followed by Kushinagar (24.35%). Floods, water logging and formation of shallow ponds are annual features in the region. Paddy is cultivated in monsoon in this region with flooding irrigation being practiced. This also provides an optimal breeding ground for culex mosquitoes. Similar results were seen in the study conducted by Singh et al in Uttar Pradesh.⁶

CONCLUSION

JE is a major public health problem prevalent in eastern part of Uttar Pradesh. There is a need of appropriate public health intervention by the policy makers to control this dreaded disease of mankind. Better treatment facilities are needed for better outcome. Information, education and communication (IEC) strategies, planning and their effective implementation has always been the mainstay of prevention. Hence adequate and specific information should be disseminated to the people regarding the determinants and factors of JE occurrence and its prevention. With the availability of a safe and effective vaccine, vaccination can play a major role to control JE.

ACKNOWLEDGEMENTS

Authors would like to thank Dr. Badri Vishal, Director of communicable diseases, Swasthya Bhawan, Lucknow (U.P.) for providing detailed information on Japanese encephalitis cases.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: The study was approved by the Institutional Ethics Committee

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