je virus is a member of the family flaviviridae , genus flavivirus and is transmitted to humans through a pig - culex mosquito - pig cycle . the clinical features are manifested as a febrile headache syndrome , aseptic meningitis or encephalitis . approximately 3 billion people live in je - endemic areas where at least 50,000 cases of je are reported every year . of these about 10,000 cases je virus can not usually be isolated from clinical specimens because of low levels of viremia and rapid development of neutralizing antibodies . the detection of je virus specific igm by igm captive - enzyme linked - immunosorbent assay ( igm - captive elisa ) has been accepted as the standard for serological diagnosis . the presence of je virus - specific igm in cerebrospinal fluid ( csf ) is considered to be a sign of je virus infection of the central nervous system . serum samples are also used for detection of specific igm , because serum can be obtained from patients more easily than csf . the candidate is an attenuated sa-14 - 14 - 2 virus strain , adjuvanted with aluminum hydroxide and also grown in vero cells . the incidence of je in india is still increasing and the case fatality rate of reported cases is high , i.e. , 1030% . however overall trends for india are difficult to predict because je endemicity is heterogenous and because socioeconomic conditions for control differ substantially from one state to another . the who national network laboratory for je started functioning in assam medical college and hospital ( amc and h ) , dibrugarh from the year 2006 . in the present study je virus specific igm in serum and csf from acute encephalitis syndrome ( aes ) patients , attending amc and h , dibrugarh from 2007 to 2009 were detected and different epidemiological parameters namely age , season , and vaccination campaign were enumerated . aes consists of patients who present with fever , altered sensorium ( including symptoms such as confusion , disorientation , coma or inability to talk ) , and new onset of seizures . the different epidemiological features were characterized depending on a pretested structured questionnaire called the clinical information form ( cif ) . the project had been approved by suitably constituted ethics committee of the institution within which the work was undertaken . clotted blood and csf were collected from aes patients within 7 days of admission to amc and h , dibrugarh . samples were collected in sterile vials and immediately transported to the laboratory of the department of microbiology , amc and h , dibrugarh . the serum was separated from the blood and both serum and csf were stored at 30c . the serum samples were tested by the panbio je - dengue igm combo elisa kit . a - z - test was used for the analytic assessment using spss 14 software . the differences were considered to be statistically significant when the p value obtained was less than 0.05 . in 2007 157 aes cases were admitted in amc and h of which 62 were positive for je . the detection rate of je was 39.4% . the total number of male cases ( age15 years ) was 12 and the number of males ( age>15 years ) was 23 . females ( age15 years ) were 11 , and 13 cases belonged to the age group of more than 15 years . in 2008 total aes cases were 276 out of which 141 cases were positive for je . a total of 23 cases were males aged15 years whereas 65 cases were males in the age group of more than 15 years . females ( age15 years ) were 17 , and 36 cases belonged to the age group of more than 15 years . the total number of male cases ( age15 years ) was 24 and the number of males ( age>15 years ) was 67 . females ( age15 years ) were 19 , and 44 cases belonged to the age group of more than 15 years [ table 1 ] . age and sex distribution of je cases in 3 years the seasonal distribution shows clustering of cases during july and august month . in 2007 , a similar picture was seen in 2008 where july had 90 cases and august had 37 cases , and in 2009 july had 85 cases and august had 54 cases [ figure 1 ] . vaccination for je was started in a phased manner in assam , a state in north east india in 2006 by the government of india in collaboration with who . in the year 2006 the vaccination program was undertaken in dibrugarh and sivasagar , two districts in the state of assam . in the subsequent year 2007 there is a definite reduction of cases of je in the age group of less than 15 years of age . cases of je increased in the age group of more than 15 years in the district where the vaccination program was undertaken . this increase of cases from pediatric to adults is also significant statistically by the z - test ( p<0.05 ) . the number of cases of je in arunachal pradesh is more in the age group of less than 15 years [ table 2 ] . there is an increase in aes cases and also je cases from 2007 to 2009 . this increase may be due to the establishment of sentinel surveillance which was started in 2006 . the male adult population were most affected as they worked outdoors and were more exposed to the vector c. tritaeniorhynchus that breed abundantly in the rice fields . assam is an endemic region for je , and here je shows a seasonal variation . the rainfall starts from the month of june and there is an increase in the mosquito population . another study in thailand indicated that nonimmune sentinel pigs in the dry hot season were not susceptible to infection until several weeks after the first rains of the weather season . one study in china also found that reduced rainfall led to a decrease in the c. tritaeniorhynchus mosquito population in 1980 and 1981 . it should be noted that the above temporal relationship may vary by different geographic areas and other factors , such as pig density and vaccine coverage rate . the finding on time lag 1 of climate variables for the southern area in taiwan suggests that it takes 1 month for temperature and precipitation to effect occurrence of je in humans . this study in taiwan also concluded that the seasonal pattern on occurrence of je cases clusters between may and august during the period from 1991 to 2005 . the number of je cases is more in the age group of more than 15 years in districts where vaccination was done . this shift of je cases from children less than 15 years to adults is significant and can be explained by high coverage of vaccinated children . this finding is very similar to a study in taiwan where the average age for onset of confirmed je cases shifted from children < 10 years to adulthood . in summary , assam is still an endemic area and je affects the adult male population here . je also shows a seasonal variation with maximum cases in the month of july and august . although vaccination campaigns with the live attenuated vaccine sa-14 - 14 - 2 has started and is protecting the under 15 children , there is a shift of disease pattern in the older population , so a concerted effort in surveillance and immunization is required to keep this vector borne disease problem in control .
aim : japanese encephalitis ( je ) virus is the leading cause of viral neurologic disease and disability in asia . in the present study je virus - specific igm in serum and csf from acute encephalitis syndrome ( aes ) patients , attending assam medical college and hospital ( amc and h ) , dibrugarh , assam from 2007 to 2009 were detected and different epidemiological parameters namely age , season and vaccination campaign were enumerated.materials and methods : a cross - sectional study on patients with aes admitted in amc and h , dibrugarh , assam was done during 2007 to 2009 . 
 the different epidemiological features were characterized depending on a pretested structured questionnaire called the clinical information form ( cif ) . 
 serum and csf obtained were tested by a panbio je - dengue igm combo elisa kit and jev chex kit ( xycton).statistical analysis : a z - test was used for the statistical analytic assessment.results:detection rate of je was 39.4% , 51.1% , and 51.3% in the years 2007 , 2008 , and 2009 respectively . 
 cases of je increased in the age group more than 15 years in the district where the vaccination program was undertaken . 
 this increase of cases from pediatric to adults is also statistically significant by the z - test ( p<0.05).conclusion : there was an increase in aes cases and also je cases from 2007 to 2009 . 
 je also showed a seasonal variation with maximum cases in the months of july and august . 
 although vaccination campaigns with the live attenuated vaccine sa-14 - 14 - 2 have started and are protecting the under-15 children , there is a shift of disease pattern in the older population .