Journal of Vector Borne Diseases

: 2021  |  Volume : 58  |  Issue : 2  |  Page : 154--158

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

P Philip Samuel1, R Govindarajan1, R Krishnamoorthi2, S Victor Jerald Leo1, V Rajamannar1, J Nagaraj3,  
1 ICMR-Vector Control Research Centre Field Station, Madurai, Tamil Nadu, India
2 ICMR-Vector Control Research Centre, Puducherry, India
3 ICMR-National Institute of Epidemiology, Chennai, Tamil Nadu, India

Correspondence Address:
Dr. P Philip Samuel
Scientist C, ICMR-Vector Control Research Centre Field Station, Department of Health Research, 4, Sarojini Street, Chinnachokkikulam, Madurai-625002, Tamil Nadu


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.

How to cite this article:
Samuel P P, Govindarajan R, Krishnamoorthi R, Leo S V, Rajamannar V, Nagaraj J. Dengue infection among tribal population in the Nilgiris district, Tamil Nadu, India.J Vector Borne Dis 2021;58:154-158

How to cite this URL:
Samuel P P, Govindarajan R, Krishnamoorthi R, Leo S V, Rajamannar V, Nagaraj J. Dengue infection among tribal population in the Nilgiris district, Tamil Nadu, India. J Vector Borne Dis [serial online] 2021 [cited 2022 May 21 ];58:154-158
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Full Text


Dengue is currently regarded globally as one of the most important mosquito-borne viral disease. Every year dengue outbreaks continue to occur in many places and the disease is expanding its territory to new geographical areas[1]. There is a 30-fold increase in the global incidence of dengue observed over the past 50 years[2]. Nowadays dengue is reported as a major global public health threat and world’s two-fifths population is at risk of acquiring dengue infection[3],[4],[5]. Transmission of dengue occurs in almost all World Health Organization (WHO) regions of the world, and more than 125 countries are known to be dengue endemic[6]. In India, in spite of many efforts, the number of dengue cases in several areas, its severity and geographical spread are extending alarmingly and thus posing dengue as a deadly disease. Dengue has emerged as an important public health problem in Tamil Nadu since 2000[7],[8]. Initially, there were sporadic cases in few districts of Tamil Nadu which later established as an endemic disease in almost all the districts of Tamil Nadu, except Nilgiris district, with major outbreaks occurred from the year 2005 onwards. Recently in Tamil Nadu, a shift in dengue outbreak occurrence was reported during the winter season (January–February) in Theni district[9].

In India, tribals constitute 8.6% of the country’s total population (Census 2011). Dengue seroprevalence studies conducted during 2011 among Irular; a semi-nomadic tribal population from the forest fringe villages of Nilgiris district showed IgM positives for dengue. There is no indepth study undertaken so far to determine the dengue epidemiological situation in the Nilgiris district of Tamil Nadu, situated in the Western Ghats. Hence this study was carried out to understand the dengue epidemiology in Nilgris district.

 Material & Methods

According to the census of India, 4.1% of tribes are living in the Nilgiris district of Tamil Nadu (Source: Nadu - Forest Department). Block wise location and elevation details are furnished below. Kotagiri is located at11.43°N 76.88°E and has an average elevation of 1847 meters (6060 ft). Gudalur is located at 11.50°N 76.50°E and has an average elevation of 1100 m (3500 ft) above sea level. Udagamandalam is located at 11.41°N 76.70°E and has an average elevation of 2240 m (7350 ft). Coonoor is located at11.35°N 76.82°E and has an average elevation of 1850 meters (6070 ft) above sea level. Based on the elevation topography and vegetation of the Nilgiris district, blocks were classified into two categories; mountainous block and hilly with forest block. The Kotagiri, Coonoor and Udagamandalam blocks are categorized as a mountainous block, rich in mountains, waterfalls, plantations, and simultaneously Gudalur block is categorized as hilly with dense forest block, rich in evergreen and deciduous forests like Mudumalai sanctuary.

The clinicians at the Nilgiris Adiwasi Welfare Association hospitals-situated in Kotagiri, Kozhikarai and Primary Health Centers (PHCs); 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. A total of 267 samples with the background information of the patients were screened for NS1 (antigen), IgM and IgG antibodies (NS1- Panbio Dengue early ELISA; IgM - Panbio Dengue IgM capture ELISA; IgG - Panbio Dengue IgG capture ELISA; Manufactured by Standard Diagnostics Inc, Republic of Korea), as per manufacturer’s protocol, at ICMR-VCRC Field Station (erstwhile ICMR-CRME), Madurai.

Ethical statement

This study was approved by the Centre’s human ethics committee.


The present study reports the dengue virus activity in the indigenous community of the Nilgiris district, Tamil Nadu [Figure 1]. Screening results of 2015–16 samples showed dengue positives with 4 NS1, 7 IgM and 1 IgG. Similarly previous year 2014–15 results showed 10 IgM and 3 IgG positives[10]. There is 8.39% dengue positivity during the first year study (2014–15) reported only from 3 blocks maximum cases recorded from Kotagiri block with 9 cases followed by Udagamandalam block with 3 cases and Gudalur with 1 case. No positive dengue case was reported from Coonoor block during the first year study. Results from 2015–16 showed that 10.71% dengue positivity again recorded from the same study area from all the four blocks. Udagamandalam block (6 nos.) reported the maximum number of dengue positives followed by Kotagiri block (3nos.), Coonoor block (2 nos.) and Gudalore block (1 no.). In particular, Udagamandalam block observed significantly (P<0.05) more cases compared to Coonoor and Gudalur blocks [Table 1].{Figure 1}{Table 1}

First year study 2014–2015 showed infection from 5 different tribes like Irular (6 nos.), Toda (1no.), Kota (3nos.), Kurumba (1no.) and Kattunaickan (1no.). During the year 2015-2016, among the different tribes, Irular reported maximum dengue positives 91.5% (11 nos.) followed by Paniya 8.3% (1no.). Among the tribes, the Irular tribe was predominantly infected with this disease (91.7%) [Table 2]. This study observed 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).{Table 2}

Dengue positives were identified from 1 (2.44%) male and 12 (10.53%) women in 2014-15 and 5 men and 7 women identified in 2015–16 [Table 3].{Table 3}


There are several human-induced factors such as changes, the rural ecology associated with the developmental process, climatic and socioeconomic condition, that enable dengue virus to spread to new virgin areas. The rapid growth of building activities, improvement of transport facilities such as railway and roads, increased movement of people from different areas and environmental changes have all favored the spread of dengue[10]. During the study 13 dengue positive cases in 2014–15 and 12 cases in the subsequent year 2015–16 were reported. There is an overlapping zone for the breeding of the two vector species, viz, Aedes aegypti and Ae. albopictus which are the peridomestic areas where these 2 species share common breeding grounds, (i.e.) waste tyres and cemetery vases, as already reported[11].

A person belonging to Irular tribe (M 35 yrs) from Annaikatti (Elevation 1802 M) village which is situated in Udagamandalam block at higher altitude was found positive for dengue IgM during June 2015. He commutes daily from Annaikatti to Coimbatore for occupation and returns back to his native village. The eastern slopes of the Nilgiris hills (200–500m) are bounded by Coimbatore district of Tamil Nadu. Dengue epidemics were reported in Coimbatore from 1998 onwards. The dengue virus is maintained in Coimbatore (urban area) by Ae. aegypti - human - Ae. aegypti with periodic/cyclic epidemics[12]. Dengue fever cases are reported in peripheral and rural areas of Coimbatore district in Tamil Nadu. Thus, dengue virus from urban localities can easily spread to tribal areas when the male members migrate/move daily from one place to other for job opportunities, as already reported in other areas[13],[14]. In the Annaikatti village, besides this person reported earlier, 3 other persons belonging to same Irular tribe from the same area were found with dengue infection - his wife 32 years female was tested positive for NS1 antigen and his two neighbors 50 and 70 yr male residing on either side of his house were tested NS1 positive. Thus, the virus could have been brought from Coimbatore, a dengue endemic urban area. The virus could be disseminated from the community living in lower altitude to those residing at higher altitudes. This study suggested that dengue infection is no more restricted to an urban area, but is an example of reverse arbovirus infection extending its arms to rural areas as reported in tribal villages of Mandla district, Madhya Pradesh,[13] Arunachal Pradesh a hilly state in Northeast India[14] and in other parts of India[15]. Improved road connectivity in these areas promoted agricultural settlements and increased the Aedes albopictus abundance to spread dengue among tribal communities[16]. Similarly, Dengue epidemics in many places were influenced by nearby/neighboring countries as seen in China imported from Southeast Asian countries[17] and in Europe imported from Venezuela[18].

Gender wise dengue positive results in Nilgiris showed that positives were recorded mostly from females exposed to dengue vector bites in the field engaged in harvesting or cultivation in the first year as observed in Penang Island in Malaysia[19], in Kolkata in 2010[20] and also in a hilly state of Arunachal Pradesh in Northeast India[14].

This area with low socioeconomic challenges is considered as a suitable place for the maintenance of vector mosquitoes which may also facilitate the transmission of DENV[21],[22]. This study unearthed the prevailing hidden mosquito-borne dengue disease among these downtrodden and socio-economically weaker section of the indigenous people present in Nilgiris district. Since people acquire the dengue infection from working places and educational institutions, the community should be sensitized about this and suggested to use personal protective measures to interrupt human-vector contact.


There should be an improvement in the preparedness of public health officials by providing prior information about outbreaks by linking environmental variables with disease system which can help reduce fatality rates among these groups. This study created awareness about the dengue prevalence among the tribal community and a need for a permanent dengue surveillance system with improved disease diagnostics, to initiate effective antidengue treatment measures and also to take up appropriate vector control efforts to stop dengue transmission from this hilly region.

Conflict of Interest: None


Authors thank the Secretary, Department of Health Research (DHR), Ministry of Health & Family Welfare and the Director General, ICMR for financial support and Dr. B. K. Tyagi for providing the facilities and for their encouragement, guidance and useful suggestions for the study. Sincere thanks are due to Director, ICMR-VCRC and all the supporting staff of ICMR-VCRC FS, Madurai (erstwhile ICMR-CRME). We gratefully acknowledge DPH&PM, Chennai, Tamil Nadu, Secretary, Nilgiris Adivasi Welfare Association (NAWA) Kotagiri and Director, Tribal Research Centre, Udhagamandalam for their wholehearted support in this endeavor.


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