Dengue infection among tribal population in the Nilgiris district, Tamil Nadu, India.

BACKGROUND & OBJECTIVES: Dengue emerged as an important public health problem in Tamil Nadu from 2000 onwards, reported in all the districts as an endemic disease of Tamil Nadu except Nilgiris district. So this study was carried out to understand the dengue epidemiology in Nilgiris district. METHODS: Block-wise study was made at the Nilgiris district. The clinicians at the Nilgiris Adivasi Welfare Association hospitals (NAWA) situated in Kotagiri, Kozhikarai and Primary Health Centers from Kunjpannai, Arayoor, and Soloor Mattam, examined and recorded symptoms and collected blood samples from the dengue-suspected patients. These samples were centrifuged at 4°C and stored. Serum samples (267 nos.) collected from dengue-suspected patients for two years period from 2014 to 2016 were screened for dengue infection. RESULTS: First year study conducted during 2014-15 showed 13 dengue positives (8.39%) mainly from Kotagiri block (9 nos. - 69.2%) and the second year study conducted during 2015-16 showed 12 dengue positives (10.71%) found mostly from Udagamandalam block (6 nos.- 50%). People belonging to 6 different tribes - Irular, Toda, Kota, Kurumba, Kattunaickan, and Paniya were found infected with dengue and more Irular positives were recorded in both the years (5 Irular-2014-15 & 11 Irular -2015-16). First year detected more female positives (92.3%) whereas the second year showed 5 males (41.7%) and 7 females (58.3%). INTERPRETATION & CONCLUSION: This study unearthed the hidden disease dengue to be prevalent among the tribal community and emphasized the need for the establishment of a permanent dengue surveillance system with improved disease diagnostics, to initiate effective vector control efforts to stop dengue transmission from this hilly region.

Emergence of dengue in the tribal pockets of Nilgiris district, Tamil Nadu.

As original tribal ways of living have morphed from a forest dweller existence, dengue is no longer an urban infection but is now also found in rural hilly areas. The spread of dengue is enhanced by the frequent movement of people to endemic areas where there is a vector mosquito presence. The impact of the virus is known to be great in the immunologically naive population. Our study reports on the threat of the dengue virus in these hilly areas.

Diagnosis of Chikungunya dominated co-infection with dengue during an outbreak in south India (2010 and 2012).

Following a report of dengue outbreak from January 2010 to 2012 in the Tirunelveli, Theni, Dharmapuri and Thiruvallur districts of Tamil Nadu state, India, an investigation was carried out. The study was to demonstrate the probable presence of Chikungunya viral antibodies in patients clinically suspected of dengue fever. Out of 331 samples analysed, dengue viral antibodies were observed in 14.8% (n = 49) of patients, while 16.6% (n = 55) were positive for Chikungunya viral specific IgM antibodies. In the four districts surveyed, patients found positive for Chikungunya were found to be higher than dengue. The clinician should consider Chikungunya in the differential diagnosis of dengue-like infection appearing in the community.

Molecular identification of mosquito vectors using genomic DNA isolated from eggshells, larval and pupal exuvium.

Correct and precise identification of mosquito vectors is important in many respects including development of vector control strategies. Conventional identification methods have limitations for sibling and closely related species of mosquitoes, stage and quality of the specimen used and this could be overcome by DNA-based identification methods using molecular markers such as nuclear ribosomal internal transcribed spacer (ITS) which do not demand intact or undamaged specimen. Genomic DNA is usually isolated from whole mosquito, legs, wings etc. Alternate sources for genomic DNA isolation such as eggshells, larval and pupal exuviae were explored in this study by amplifying the ITS markers. Standardization of genomic DNA extraction and ITS amplification were carried out with laboratory specimens. The same was applied to specimens collected from the field. The results show that PCR amenable genomic DNA could be isolated from fresh exuviae collected in the laboratory and not from older and/or field specimens. But exuviae of larvae and/or pupae collected in the field reared to adulthood in the laboratory yielded PCR amenable genomic DNA. The results also revealed that the ITS2 marker could very well differentiate Aedes aegypti and Aedes albopictus by producing amplicons of ~330 bp and ~520 bp, respectively. The genomic DNA from these alternate sources also supported the species-specific PCR to distinguish the Culex vishnui subgroup mosquitoes.