Emergence of dengue in tribal villages of Mandla district, Madhya Pradesh, India

Abstract

Background & objectives: Dengue (DEN) is a rapidly spreading arboviral disease transmitted by Aedes mosquitoes. Although it is endemic in India, dengue virus (DENV) infection has not been reported from tribal areas of Madhya Pradesh. Investigations were conducted to establish the aetiology of sudden upsurge of cases with febrile illness in June 2013 from tribal villages of Mandla district of Madhya Pradesh, India.

Methods: The rapid response team of the National Institute for Research in Tribal Health, Jabalpur, conducted clinical investigations and field surveys to collect the samples from suspected cases. Samples were tested using molecular and serological tools. Collected mosquitoes were identified and tested for the presence of virus using semi nested reverse transcriptase-polymerase chain reaction (nRT-PCR). The sequences were analysed to identify serotype and genotype of the virus.

Results: Of the 648 samples collected from 18 villages of Mandla, 321 (49.53%) were found to be positive for dengue. The nRT-PCR and sequencing confirmed the aetiology as dengue virus type 2. Eighteen per cent of patients needed hospitalization and five deaths were attributed to dengue. The virus was also detected from Aedes aegypti mosquito, which was incriminated as a vector. Phylogenetic analysis revealed that the dengue virus 2 detected belonged to cosmopolitan genotype of the virus.

Interpretation & conclusions: Dengue virus serotype 2 was detected as the aetiological agent in the outbreak in tribal villages of Mandla district of Madhya Pradesh. Conducive man-made environment favouring mosquitogenic conditions and seeding of virus could be the probable reasons for this outbreak. Urgent attention is needed to control this new threat to tribal population, which is already overburdened with other vector borne diseases.

Fig. 1

Age, sex distribution of the suspected and confirmed dengue cases from Mandla district (X axis, age groups in years, M= males; F, females. The number in and on the top of bars indicate total cases, Y axis, number of cases; #, the most affected group [OR= 1.90 (95%CI = 1.06-3.4) P=0.03];★, death cases.

Fig. 2

Maximum likelihood phylogenetic tree, generated with Kimura 2-parameter using CLUSTAL W & MEGA 5 software with 1000 bootstrap replicates. Twenty four reported sequences of DENV2 were downloaded from NCBI and were assembled with the six curated (marked with ■= human, ▲ = mosquito) sequences of E/NS1 gene junction of DENV2 from this study. DENV3 used as out group. The analysis reveals that virus belongs to cosmopolitan genotype of DENV2.