First report of Chikungunya virus circulation during a dengue outbreak in Arunachal Pradesh, a Northeastern state of India

Dengue has become a major public health problem in Pasighat, Arunachal Pradesh since 2012 outbreak. This region is rich in Aedes mosquitoes, the common vector for Dengue and Chikungunya (CHIK), however, active surveillance of CHIK is lacking in this part of India. Therefore, this study has been undertaken to detect the presence of CHIKV infection during 2014 and 2015 dengue outbreak in Arunachal Pradesh. A total of 116 (52 during 2014 and 64 during 2015 outbreak) dengue negative serum samples were collected from General Hospital, Pasighat and were screened for the presence of CHIK IgM antibodies. All the samples were further processed for CHIKV RNA detection by RT-PCR using specific primers. Phylogenetic tree was constructed by Neighbor Joining method using Kimura-2 parameter model. A total of 8 samples were found to be positive for IgM antibodies. RT-PCR showed CHIKV RNA positivity in 2 samples. Both of these samples belonged to 2014 outbreak. Phylogenetic tree revealed that the CHIKV circulating during the outbreak belonged to Eastern, Central and Southern African genotype. Sequence analysis showed two uniform nucleotide substitutions. Circulation of CHIKV masked by dengue is reported from this study. Therefore, CHIKV diagnosis should be made as a routine test in areas where dengue is already endemic so as to prevent misdiagnosis of the disease and to check its accomplishment before commencing an outbreak.