HABITAT ANALYSIS OF MALARIA VECTOR SPECIES

Transcription

1 CHAPTER V HABITAT ANALYSIS OF MALARIA VECTOR SPECIES 5.1 Mosquito survey in different habitat types Habitat identification of transmitting malaria is an important part of the analysis for delineating the areas prone to malaria. A habitat determines the proliferation of in an area as different genera of mosquito prefer different types of habitats. From the earlier studies on mosquito breeding habitats (Dev, 1996a; Sharma et al., 28; Rohini et al., 21), it has been established that anopheline mosquito which is the vector responsible for malaria, breeds in slow flowing stream that come out from the high altitude areas. On the other hand, Culex that spread Japanese encephalitis and filariasis breed in stagnant water such as water in paddy fields, drains etc. Aedes transmitting dengue prefer breeding in small pools of stagnant water like in tyres, plastic cups, flower pots, desert-coolers etc. Hence it is obvious that the species composition of the in different regions vary with the availability of suitable breeding habitats. A survey was conducted in several parts of Sonitpur district to find out the abundance and distribution of different mosquito species in specific breeding sites. The study was carried out from 21 different sites, which are of different physical nature (Fig. 5.1). The adult were captured by light traps designed by the U.S. Centres for Disease Control, popularly known as Centre for Disease Control (CDC), which are operated by a 6 volt battery. In this method the 89

2 are attracted by the light and get in a bag with the help of a fan attached to the trap. The selection of the mosquito trapping sites was made on the basis of random selection of houses from the study area considering the different physiographical conditions in the district. A minimum of six trap collections were obtained from each of the study sites. In some cases the traps were more than six. The collections were made from both human dwellings and cattle sheds. The latitudinal and longitudinal co-ordinate positions of the selected sites were marked with Garmin Oregon 55 GPS device to locate exact position of CDC light traps. An approximate distance of around 5 metres was maintained to obtain reliable information on spatial variation of types. Geographical Information System (GIS) was used for better interpretation of the mosquito distribution pattern wherein GPS data and mosquito types in the field were integrated. Figure 5.1: Mosquito survey sites 9

3 A buffer of 2 kilometres from the point of mosquito trap sites was created using GIS software, considering the flight range of mosquito. It has been assumed that the collected in each trap travelled up to a flight range of 2 kilometres before getting captured in the CDC light trap. The same buffer of 2 kilometres from each site was used to mask the land use land cover (LULC) map that was generated from the LISS III satellite image (Fig. 5.2). The purpose is to find the correlation between different categories of land use features within the flight range of in a site and the mosquito species collected in the same site. Figure 5.2: Buffer of 2 km around survey sites and superimposition over LULC types Mosquitoes belonging to the genera Anopheles, Culex, Mansonia, Armigeres and Aedes were recorded from the survey sites of the district. The density of belonging to each of these genera was estimated in each site. Anopheles is sub categorised into three groups primary malaria vector, secondary 91

4 malaria vector and non-vectors of which primary and secondary mosquito vectors are mainly responsible for malaria. 5.2 Geo-environmental setting of mosquito habitats During the field survey different mosquito species under different genera of mosquito were captured inside the CDC traps in 21 sites under surveillance. The highest collection of per trap night (per trap night density) was recorded from Kalabari followed by Thelamara, Dhobikata, Tetunbari, Sialmari and Rangapara survey sites (Table 5.1 and Fig. 5.3). The collected were identified based on standard keys taking help from a team of medical entomologists of the Defence Research Laboratory, Tezpur under Defence Research and Development Organisation (DRDO). The that were identified by experts belong to genera of Anopheles, Culex, Mansonia, Adeas etc. It is a fact that only a few among the many mosquito species spread diseases like malaria, Japanese encephalitis, filariasis, dengue, chikungunya, west nile etc. These species are known as disease vectors. Some species of Anopheles are malaria vectors, whereas there are other species which are non vectors. The Anopheles vectors of malaria are classified into primary and secondary vectors. The primary vectors always prefer human blood for laying and nurturing eggs and thereby transmit the parasite from one person to another. On the other hand the secondary vectors prefer birds or animals, but in the absence of them choose human blood and transmit the parasite. The primary vectors are mainly responsible for maintaining the disease transmission cycle in an area, whereas the secondary 92

5 Table 5.1: Per trap night collected from different survey sites in Sonitpur district Mosquito genera-wise density per trap night (Percentage ) Survey site Anopheles primary vector Anopheles secondary vector Anopheles non-vector Culex Mansonia Armigeres Aedes Coquilletidia Total AAMLAIGURI.3 (.11) 32.2 (1.81) 1 (33.61) (47.96) 5.7 (1.9) 15.8 (5.32).8 (.28) (.) BISWANATH CHARALI.3 (.7) 1.7 (3.51) 5.5 (11.58) 22.8 (48.7) 2.8 (5.96) 14.3 (3.18) (.) (.) 47.5 CHAPAI RAUMARI 15 (5.69) 31.7 (12.1) 48.2 (18.27) 162 (61.44) 1.2 (.44) 4.7 (1.77) 1 (.38) (.) DHOBIKATA (.) 49 (8.77) 126 (22.54) (57.9) 3.3 (.6) 49 (8.77) 8 (1.43) (.) 559. GANGMOUTHAN (.) 5.2 (2.56) 23.8 (11.81) 15.7 (74.65) 4.7 (2.31) 16 (7.93) (.) 1.5 (.74) 21.8 JAISIDDHI 2.7 (.88) 11.7 (3.87) 62.8 (2.82) 27.2 (68.64) 5.5 (1.82) 12 (3.98) (.) (.) 31.8 JAMUGURI (.) 1 (1.22) 11 (13.44) 42 (51.32) 1.5 (1.83) 24 (29.33) 1.7 (2.4).7 (.81) 81.8 KALABARI.8 (.5) 3.2 (1.72) (14.54) (18.74) (62.4) 4.5 (2.31) (.) 4.5 (.26) KHANAMUKH.3 (.4) 1.2 (1.42) 11.2 (13.56) 52.7 (62.75) 4.3 (5.26) 12 (14.57) 1.7 (2.2) (.)

6 MAINANGSHREE MISAMARI PAVOI RANGAPARA RIHAJULI SEIJOSA SIALMARI SINGRI SOLMARA TETUNBARI THANDAPANI THELAMARA 1 (2.43) 1.6 (2.38) 4.5 (6.57) 4 (1.11) 5.1 (6.3) 11.3 (1.63) 3.7 (.74) 3.2 (1.9) 1.3 (.54) (.) 1 (.38) 6.2 (.54) 2 (4.86) 8.7 (16.67) 4.7 (6.81) 8 (2.21) 18.5 (22.94) 11 (1.31) 35.2 (7.12) 3.2 (1.9) 1.4 (.57) 18.7 (3.57) 15.5 (5.83) 1.8 (.94) (62.35) 4.7 (9.1) 9.8 (14.36) 42.1 (11.66) 34.3 (42.4) 11.2 (1.47) (3.25) 56.8 (19.32) 1.6 (4.29) (27.28) 56.7 (21.32) 329 (28.65) Source: The Density per trap night are calculated by the research student based on data collected from Defence Research Laboratory, Tezpur (DRDO). The research student was actively involved in field works relating to mosquito trapping. Note: In bracket is the percentage collected (22.67) 26.4 (5.77) 33.7 (49.15) (64.55) 21.3 (26.32) 44.2 (41.41) (59.73) 159 (54.8) 17.6 (68.88) (54.75) (69.15) (3.85) (.) 1.7 (3.21) 5.5 (8.3) 2.5 (5.67) (.) 3.7 (3.44) 9.3 (1.89) 53.8 (18.3) 48.1 (19.41) 36.3 (6.95) 4.7 (1.76) 37.7 (32.27) 3.17 (7.69) (.) 9.7 (14.11) 53.4 (14.77) 1.7 (2.14) 25.3 (23.75) (.) 18 (6.12) 14.8 (5.99) 35 (6.69) 4.2 (1.57) 69.8 (6.8) (.) (.).7 (.97) (.) (.) (.) (.) (.) (.) 2.5 (.48) (.) 1.5 (.13) (.) (.) (.) (.) (.) (.) 1.3 (.27) (.).8 (.32) 1.5 (.29) (.) 6.2 (.54)

7 vectors play a supporting role. Although the non vectors also feed on human blood but they are not capable of carrying the parasite. Source: Defence Research Laboratory, Tezpur (DRDO) Figure 5.3: Mosquito density and diversity in different survey sites The collected from different trap sites of the study area reveal the diversity and variations in the density of mosquito genera (Fig. 5.4). The Anopheles are abundantly found in the northern belt of the district, which is mostly densely vegetated. The sites/places where Anopheles recorded more than 4% are Mainangshree (69.64%), Rihajuli (71.64%), Misamari (46.15%) and Aamlaiguri (44.54%) (Table 5.1). The primary vectors of 95

8 Anopheles that are responsible for malaria dominate in areas of Misamari (2.38%), Seijosa (1.63%), Pavoi (6.57%), Rihajuli (6.3%) and Chapai Raumari (5.69%). The areas where secondary vector dominates by more than 1% are Rihajuli (22.94%), Misamari (16.67%), Chapai Raumari (12.1%), Aamlaiguri (1.81%) and Seijosa (1.31%). The availability of Anopheles vector in these sites indicates the risk for malaria in the human population. Source: Defence Research Laboratory, Tezpur (DRDO) Figure 5.4: Mosquito genera in different survey sites of Sonitpur district Similarly the areas where Culex dominated are located in the central part of the district. Gangmouthan, Thandapani, Solmara, Jaisiddhi, Rangapara, Khanamukh and Chapai Raumari are some of the areas where Culex 96

9 were recorded more than 6%. Kalabari and Thelamara are the areas where Mansonia mosquito genus dominated (more than 3%). These areas are located in the flood plain of Brahmaputra along the southern part of the district. Armegeres subalbatus mosquito is predominant mainly in the central part of the district. So, it is clear that the density of mosquito species varies from place to place depending upon topography and vegetation cover. While investigating the distribution pattern of Anopheles mosquito, the malaria disease carrying mosquito, variation in primary, secondary and non vectors are observed to vary from place to place (Fig. 5.5). Primary vectors of Anopheles were observed in dense forest areas. While the secondary vectors were prevalent in all the areas except the flood plains of Brahmaputra river. The Anopheles non vectors were recorded in all areas of the district. When an attempt has been made to superimpose the layers of malaria endemic areas or the hot spots, the areas signifying hotspots are found to exactly match with the areas dominated by the primary Anopheles vectors. Thus it can be stated that the habitation of the malaria vector species in some particular areas could well be correlated with the transmission of the malaria parasite. As mentioned earlier about the three elements essential for malaria transmission - mosquito, parasite and human, the presence of new settlers in the forest areas completes the cycle of malaria transmission. The new settlers are non-immune to parasite, which in turn risk their life to malaria attack, whereas the early settlers have adopted to the 97

10 parasite. The children are more prone to malaria because of their non immunity to the parasite. Source: Defence Research Laboratory, Tezpur (DRDO) Figure 5.5: Distribution of Anopheline mosquito in Sonitpur district Interpolation with the help of raster kriging techniques using spatial analyst tool of ArcGIS 9.2 software was used for better visual representation for describing mosquito species distribution in unknown locations. Interpolation overcomes the areal bias problem and the resulting isopleth maps are easier to read than choropleth maps. In a similar study in USA (Allen and Shellito, 28), which dealt with the abundance and patterns of 24 species of mosquito vectors of West Nile virus using light trap collection data, useful spatial interpolation and geostatistical mapping were done. 98

11 In this study, the interpolation technique for Anopheles primary vector was carried out and it revealed the abundance of vectors in the north-eastern part of the district (Fig. 5.6). The generated raster map shows that the most important primary vector of malaria dominates in the northern part of Dhekiajuli, Rangapara, Balipara and North Jamuguri PHCs of the district. As per record of the district health authority this northern part of the district is a malaria endemic area. The presence of primary vectors of malaria and the parasite produce ample scope for transmission of malaria in the concerned area. Superimposing the malaria epidemiological map, a close relationship and association of vector and parasite has been observed in this part of the study area, thereby suggesting high endemicity of malaria. Figure 5.6: Dominance of Anopheles primary vectors in Sonitpur district 99

12 The interpolation of Anopheles secondary vectors revealed the dominance of secondary vectors in the eastern part of the district (Fig. 5.7). The raster image generated after interpolation shows the dominance of secondary vector in Gohpur and Behali PHCs of the district. Though the risk is high for malaria because of secondary vectors, the absence/lower transmission of malaria parasite in this part of the region shows low risk of malaria. The situation cannot be over ruled as fresh input of parasite in the population may results in emergence of malaria cases in succeeding years in this part of the region. Figure 5.7: Dominance of Anopheles secondary vectors in Sonitpur district 5.3 Distribution of breeding grounds and colonization of vectors The favourable mosquito breeding areas vary from genus to genus and species to species. The Anopheles mosquito generally prefers to breed in slow 1

13 flowing streams and rivers. The grasses that grow abundantly near the slow flowing streams offer faourable breeding grounds for colonization of Anopheles mosquito. Similarly, paddy fields are suitable sites for vector breeding during monsoon seasons. Mosquitoes like Culex and Mansonia prefer different habitats to breed. To find the relation between land use and habitatas of, an attempt has been made by masking buffer of 2 km around the survey trap sites in the LULC map. Percentages of both LULC under different categories like wetlands, marshy lands, river, normal vegetation, dense forest, agricultural fields, damp and sandy areas and mosquito genus like Anopheles (both primary and secondary), Culex, Mansonia and others have been considered for the analysis (Fig. 5.8 and Table 5.2). Figure 5.8 (a): Land Use Land Cover (LULC) in Chapai Raumari under buffer of 2 km from mosquito trap site Table 5.2 (a): Different mosquito species at Chapai Raumari trap site Mosquito genus Percentage Anopheles (A+B+C) An. Primary (A) 5.69 An. Secondary (B) 12.1 An. Non vector (C) Malaria vector (A+B) 17.7 Culex Mansonia.44 Others

14 Figure 5.8 (b): Land Use Land Cover (LULC) in Misamari under buffer of 2 km from mosquito trap site Table 5.2 (b): Different mosquito species at Misamari trap site Anopheles (A+B+C) An. Primary (A) 2.38 An. Secondary (B) An. Non vector (C) 9.1 Malaria vector (A+B) 37.5 Culex 5.77 Mansonia 3.21 Others The LULC types and mosquito species collected from Chapai Raumari area/site are taken for the analysis (Fig.5.8a and table 5.2a).The area/site is located in the north-western corner of the district under Dhekiajuli PHC. The 2 kilometre buffer created around this mosquito collected site comprises 51.84% of vegetated areas followed by 37.25% of agricultural fields and 9.75% of dense forest areas. The collected from this site comprise 61.44% of Culex and 35.97% of Anopheles species. Among the Anopheles, about 17.7% consist of vectors responsible for malaria of which 5.69% are Anopheles primary vectors and rest 12.1% are Anopheles secondary vectors. 12

15 Misamari located in the north-western part of the district under Dhekiajuli PHC contains 56.74% of dense forest areas followed by 29.25% of vegetated area, 11.49% of agricultural fields and 1.63% of marshy lands under LULC types (Fig.5.8b and table 5.2b). The highest percentage of collected from Misamari area/site comprises 5.77% of Culex species followed by 46.15% of Anopheles species. Among Anopheles 2.38% are primary vectors and 16.67% are secondary vectors. Combining both counts 37.5%, which is the percentage of responsible for malaria. Table 5.2 (c): Different mosquito species at Singri trap site Anopheles (A+B+C) 21.5 An. Primary (A) 1.9 An. Secondary (B) 1.9 An. Non vector (C) Malaria vector (A+B) 2.18 Culex 54.8 Mansonia 18.3 Others 6.12 Figure 5.8 (c): Land Use Land Cover (LULC) in Singri under buffer of 2 km from mosquito trap site Singri under Dhekiajuli PHC is situated near the north bank of Brahmaputra River (Fig.5.8c and table 5.2c). The categories under LULC types of Singri accounts 44.37% of agricultural fields followed by 27.75% of vegetated 13

16 area and 1.84% of sandy area. The collected from the area/site consists 54.8% of Culex species, 21.5% of Anopheles species and 18.3% of Mansonia species. Both Anopheles primary and Anopheles secondary vectors responsible for malaria from this area comprises 2.18% of. Survey carried out in the locality of Thelamara area under Dhekiajuli PHC contains 68.92% of area under agricultural fields and 19.67% of area under vegetation of LULC types (Fig.5.8d and table 5.2d). Mosquitoes collected from the Thelamara area/site consists of almost equal numbers of mosquito species viz. Mansonia species (32.27%), Culex species (3.85%) and Anopheles species (3.13%). Only 1.48% of under Anopheles primary and Anopheles secondary vectors are collected from the different trap sites. Figure 5.8 (d): Land Use Land Cover (LULC) in Thelamara under buffer of 2 km from mosquito trap site Table 5.2 (d): Different mosquito species at Thelamara trap site Anopheles (A+B+C) 3.13 An. Primary (A).54 An. Secondary (B).94 An. Non vector (C) Malaria vector (A+B) 1.48 Culex 3.85 Mansonia Others

17 Figure 5.8 (e): Land Use Land Cover (LULC) in Mainangshree under buffer of 2 km from mosquito trap site Table 5.2 (e): Different mosquito species at Mainangshree trap site Anopheles (A+B+C) An. Primary (A) 2.43 An. Secondary (B) 4.86 An. Non vector (C) Malaria vector (A+B) 7.29 Culex Mansonia Others 7.69 Figure 5.8 (f): Land Use Land Cover (LULC) in Rihajuli under buffer of 2 km from mosquito trap site Table 5.2 (f): Different mosquito species at Rihajuli trap site Anopheles (A+B+C) An. Primary (A) 6.3 An. Secondary (B) An. Non vector (C) 42.4 Malaria vector (A+B) Culex Mansonia Others

18 Mainangshree located under Balipara PHC consists of an overall of 82.47% area under forest category (43.85% under vegetation and 38.62% under dense forest) under LULC types. Agricultural field comprises 7.9% followed by 4.36% under wetlands and 3.3% under damp area (Fig.5.8e and table 5.2e). Mosquito under categories of Anopheles species and Culex species consist of 69.64% and 26.67% respectively which are collected from the study site. Malaria causing vectors i.e. Anopheles primary and secondary contains 7.29% of. The land use pattern from the study site of Rihajuli consists of 43.85% of land under vegetation followed by 38.62% under dense forest and 7.9% under agricultural fields (Fig.5.8f and table 5.2f). The mosquito collected from Rihajuli area/site contains 71.64% of Anopheles species and 26.32% of Culex species. Vectors responsible for malaria consist of 29.24% (6.3% of primary vectors and 22.94% of secondary vectors). Survey carried out in Rangapara area contains 54.94% of LULC area under vegetation followed by 31.61% under agricultural fields, 8.26% under dense forest and 4.22% under marshy lands (Fig.5.8g and table 5.2g). Mosquitoes collected from the survey area/site in Rangapara comprise 64.55% of Culex mosquito species, 14.98% of Anopheles mosquito species, 14.77% of other species and 5.67% of Mansonia mosquito species. 16

19 Figure 5.8 (g): Land Use Land Cover (LULC) in Rangapara under buffer of 2 km from mosquito trap site Table 5.2 (g): Different mosquito species at Rangapara trap site Anopheles (A+B+C) An. Primary (A) 1.11 An. Secondary (B) 2.21 An. Non vector (C) Malaria vector (A+B) 3.32 Culex Mansonia 5.67 Others Figure 5.8 (h): Land Use Land Cover (LULC) in Khanamukh under buffer of 2 km from mosquito trap site Table 5.2 (h): Different mosquito species at Khanamukh trap site Anopheles (A+B+C) An. Primary (A).4 An. Secondary (B) 1.42 An. Non vector (C) Malaria vector (A+B) 1.82 Culex Mansonia 5.26 Others

20 Khanamukh under Balipara PHC has 68.68% of agricultural fields under land use cover followed by vegetation (23.42%), marshy lands (5.4%) and damp area (1.92%) under different LULC types (Fig.5.8h and table 5.2h). In term of, concentration of Culex mosquito species (62.75%) was found higher followed by Anopheles species (15.38%), others species (16.6%) and Mansonia species (5.26%) collected from the survey area/site of Khanamukh. Figure 5.8 (i): Land Use Land Cover (LULC) in Solmara under buffer of 2 km from mosquito trap site Table 5.2 (i): Different mosquito species at Solmara trap site Anopheles (A+B+C) 5.4 An. Primary (A).54 An. Secondary (B).57 An. Non vector (C) 4.29 Malaria vector (A+B) 1.11 Culex Mansonia Others 6.31 Solmara situated in the central part of the district near to Tezpur town under Balipara PHC has 48.45% of agricultural fields under LULC type (Fig.5.8i and table 5.2i). The second highest area under land cover is vegetation that comprises an area of % followed by marshy land of 9.8%, damp area of 2.27% and 1.17% under dense forest. The collected from different 18

21 trap site in Solmara comprises highest of Culex species (68.88%) followed by Mansonia species (19.41%), other species (6.31%) and Anopheles species (5.4%). Malaria contributing mosquito vectors i.e. Anopheles primary and secondary constitute only 1.11%. Figure 5.8 (j): Land Use Land Cover (LULC) in Jamuguri under buffer of 2 km from mosquito trap site Table 5.2 (j): Different mosquito species at Jamuguri trap site Anopheles (A+B+C) An. Primary (A) An. Secondary (B) 1.22 An. Non vector (C) Malaria vector (A+B) 1.22 Culex Mansonia 1.83 Others The LULC types under Jamuguri area constitute agricultural fields (7.76%), vegetation (2.61%), marshy land (3.37%) and damp area (3.25%) (Fig.5.8j and table 5.2j). The mosquito species accumulated from the area/site include 51.32% of Culex species followed by 32.18% of other mixed species, % of Anopheles species and 1.83% Mansonia species. The mosquito responsible for transmitting malaria constitutes 1.22% of the total mosquito collected. 19

22 Figure 5.8 (k): Land Use Land Cover (LULC) in Dhobikata under buffer of 2 km from mosquito trap site Table 5.2 (k): Different mosquito species at Dhobikata trap site Anopheles (A+B+C) An. Primary (A) An. Secondary (B) 8.77 An. Non vector (C) Malaria vector (A+B) 8.77 Culex 57.9 Mansonia.6 Others 1.2 Dhobikata area located under Jamuguri PHC contains 7.9% of agricultural field, 25.49% of vegetation, 2.59% of marshy land and 1.46% of dense forest area under LULC types within two kilometer buffer area around mosquito trap sites (Fig.5.8k and table 5.2k). The collected from Dhobikata area/site are sorted out into Culex species comprising 57.9% followed by Anopheles species with 31.31% and other species of 1.2%. The vectors causing malaria constitute 8.77% of Anopheles mosquito. Jaisiddhi area under Jamuguri PHC from the study site constitutes 62.1% of areas under agricultural fields followed by vegetation (34.3%) and dense forest (2.69%) under LULC types (Fig.5.8l and table 5.2l). The collected from the area/site of Jaisiddhi comprises 68.64% of Culex species followed by 11

23 25.57% of Anopheles species, 3.98% of other species and 1.82 % of Mansonia species. Mosquito causing malaria counts 4.75% of which Anopheles secondary vectors comprise mostly of 3.87%. Figure 5.8 (l): Land Use Land Cover (LULC) in Jaisiddhi under buffer of 2 km from mosquito trap site Figure 5.8 (m): Land Use Land Cover (LULC) in Seijosa under buffer of 2 km from mosquito trap site Table 5.2 (l): Different mosquito species at Jaisiddhi trap site Anopheles (A+B+C) An. Primary (A).88 An. Secondary (B) 3.87 An. Non vector (C) 2.82 Malaria vector (A+B) 4.75 Culex Mansonia 1.82 Others 3.98 Table 5.2 (m): Different mosquito species at Seijosa trap site Anopheles (A+B+C) An. Primary (A) 1.63 An. Secondary (B) 1.31 An. Non vector (C) 1.47 Malaria vector (A+B) 2.94 Culex Mansonia 3.44 Others

24 Figure 5.8 (n): Land Use Land Cover (LULC) in Pavoi under buffer of 2 km from mosquito trap site Table 5.2 (n): Different mosquito species at Pavoi trap site Anopheles (A+B+C) An. Primary (A) 6.57 An. Secondary (B) 6.81 An. Non vector (C) Malaria vector (A+B) Culex Mansonia 8.3 Others 15.9 Seijosa located north under Jamuguri PHC under land use land cover types contains vegetation (65.73%), agriculture fields (12.38%), dense forest (12.22%), marshy land (6.25%) and damp area (1.7%) (Fig.5.8m and table 5.2m). Mosquitoes species collected from the different area/site consist of 41.41% of Culex species, 31.41% of Anopheles species, 23.75% of other species and 3.44% of Mansonia species. 2.94% of under the category of Anopheles primary and Anopheles secondary vector carrying malaria were collected from this area. Pavoi trap site under Biswanath Charali PHC comprises 64.17% areas of agricultural fields, 3.46% of vegetation, 3.12% of dense forest and 1.58% of 112

25 marshy lands under LULC types (Fig.5.8n and table 5.2n). Mosquitoes collected from the area/site contain 49.15% of Culex species, 27.74% of Anopheles species, 15.9% of others species and 8.3% of Mansonia species. Malaria contributing mosquito was found to be 13.38% mosquito collected. In Biswanath Charali under different LULC types, the higher percentage of land found is agricultural fields (39.42%) followed by vegetation (34.46%), river (8.17%), dense forest (5.32%), damp area (4.86%), marshy land (3.59%) and sandy area (3.58%) (Fig.5.8o and table 5.2o). On the other hand, collected from different area/site contribute 48.7% of Culex species, 3.18% of other species, 15.79% of Anopheles species and 5.96% of Mansonia species. Of the total 4.21% are vector transmitting malaria found in the area Figure 5.8 (o): Land Use Land Cover (LULC) in Biswanath Charali under buffer of 2 km from mosquito trap site Table 5.2 (o): Different mosquito species at Biswanath Charali trap site Mosquito genus Percentage Anopheles (A+B+C) An. Primary (A).7 An. Secondary (B) 3.51 An. Non vector (C) Malaria vector (A+B) 4.21 Culex 48.7 Mansonia 5.96 Others

26 Gangmouthan situated south of Behali PHC near river Brahmaputra with different LULC types consists of 44.33% of agriculture fields followed by 24.11% of vegetation, 13.74% of damp area, 9.98% of sandy area, 2.58% of marshy land and 2.3% of dense forest (Fig.5.8p and table 5.2p). Mosquitoes collected from the area/site comprises Culex species (74.65%), Anopheles species (14.37%), other species (8.67%) and Mansonia species (2.31%). 2.56% of collected from the site are Anopheles vectors responsible for malaria. Figure 5.8 (p): Land Use Land Cover (LULC) in Gangmouthan under buffer of 2 km from mosquito trap site Table 5.2 (p): Different mosquito species at Gangmouthan trap site Anopheles (A+B+C) An. Primary (A) An. Secondary (B) 2.56 An. Non vector (C) Malaria vector (A+B) 2.56 Culex Mansonia 2.31 Others 8.67 Sialmari area located in the north under Behali PHC consists of 53.66% areas of agricultural fields under LULC type followed by 23.18% of vegetation and 21.78% of dense forest type (Fig.5.8q and table 5.2q). The gathered from the different trap sites under Sialmari area comprises 59.73% of 114

27 Culex species, 38.11% of Anopheles species and 1.89% of Mansonia species. The Anopheles primary and secondary vector together comprise 7.86% of from this area. Figure 5.8 (q): Land Use Land Cover (LULC) in Sialmari under buffer of 2 km from mosquito trap site Figure 5.8 (r): Land Use Land Cover (LULC) in Thandapani under buffer of 2 km from mosquito trap site Table 5.2 (q): Different mosquito species at Sialmari trap site Anopheles (A+B+C) An. Primary (A).74 An. Secondary (B) 7.12 An. Non vector (C) 3.25 Malaria vector (A+B) 7.86 Culex Mansonia 1.89 Others.27 Table 5.2 (r): Different mosquito species at Thandapani trap site Anopheles (A+B+C) An. Primary (A).38 An. Secondary (B) 5.83 An. Non vector (C) Malaria vector (A+B) 6.21 Culex Mansonia 1.76 Others

28 Thandapani, another area under Behali PHC under LULC type contains 44.24% of agricultural fields followed by 32.3% of vegetation, 2.6% of dense forest and 2.41% of marshy land (Fig.5.8r and table 5.2r). The collected from the area/site contains 69.15% of Culex species, 27.52% of Anopheles species, 1.76% and 1.57% of Mansonia and other species respectively. 6.21% of collected are found to be under the category of vectors responsible for malaria. Tetunbari under Gohpur PHC comprises an area of agricultural fields (59.73%), vegetation (28.43%), dense forest (7.29%), marsh land (3.2%) and damp area (1.25%) under different land use types (Fig.5.8s and table 5.2s). The mosquito collected from the site contains Culex species of 54.75%, Anopheles species of 3.85%, other species of 7.46% and Mansonia species 6.95% respectively. The vectors of malaria comprises 3.57% of Anopheles mosquito. Aamlaiguri situated north under Gohpur PHC contains 45.56% area of agricultural fields under LULC type followed by 39.81% of area under vegetation, 12.8% under dense forest and 1.71% of area under marshy land (Fig.5.8t and table 5.2t). The mosquito collected from the area/site of Aamlaiguri contains mainly of Culex and Anopheles species (47.96% and 44.54% respectively). The vectors combining both Anopheles primary and secondary that transmit malaria are found to be 1.92% in this area. 116

29 Figure 5.8 (s): Land Use Land Cover (LULC) in Tetunbari under buffer of 2 km from mosquito trap site Table 5.2 (s): Different mosquito species at Tetunbari trap site Anopheles (A+B+C) 3.85 An. Primary (A) An. Secondary (B) 3.57 An. Non vector (C) Malaria vector (A+B) 3.57 Culex Mansonia 6.95 Others 7.46 Figure 5.8 (t): Land Use Land Cover (LULC) in Aamlaiguri under buffer of 2 km from mosquito trap site Table 5.2 (t): Different mosquito species at Aamlaiguri trap site Anopheles (A+B+C) An. Primary (A).11 An. Secondary (B) 1.81 An. Non vector (C) Malaria vector (A+B) 1.92 Culex Mansonia 1.9 Others

30 Kalabari situated in south-east direction of Gohpur PHC under land use land cover contains agricultural fields (58.7%) followed by vegetation (26.58%), marshy land (7.4%), dense forest (4.38%), wetlands (2.53%), and damp areas (1.34%) (Fig.5.8u and table 5.2u). The mosquito species collected from the different site within the area contain mainly of Mansonia species (62.4%) followed by Culex species (18.74%) and Anopheles species (16.3%). The Anopheles vectors causing malaria in the area contain only 1.77 % mosquito collected. Figure 5.8 (u): Land Use Land Cover (LULC) in Kalabari under buffer of 2 km from mosquito trap site Table 5.2 (u): Different mosquito species at Kalabari trap site Anopheles (A+B+C) 16.3 An. Primary (A).5 An. Secondary (B) 1.72 An. Non vector (C) Malaria vector (A+B) 1.77 Culex Mansonia 62.4 Others 2.56 In all the 21 sites discussed above, different mosquito species are found to colonize. The land use patterns within the buffer of two kilometers from each of the trap sites are also analysed. Then both the mosquito types and land use types 118

31 are correlated to reveal their relationship. From the analysis it has come to notice that the percentage of area under agricultural fields is high in all survey sites and the percentage of Culex mosquito in the agricultural areas is also found high. Similarly, the percentage of Anopheles mosquito is found high in the case of dense forest type of land use. Table 5.3: Pearson s correlation among different types of and land use land cover types Mosquito Anopheles Anopheles Anopheles Anopheles Vectors for Culex Mansonia types primary secondary non vector Malaria LULC types (A) (B) (A+B) Wetlands.466* * *.287 Marshy lands -.58* * * River Vegetation Dense forest.725*.754*.799* * Agri. fields -.52* -.674* -.683* * Damp area Sandy area *. Correlation is significant at the.5 level (2-tailed). In order to examine correlation, if any between LULC types and mosquito species types with a view to establishing relationship and association of mosquito types with habitats, a two tailed Pearson s correlation technique has been calculated using SPSS software. Under different types of the Anopheles, Culex, Mansonia, Anopheles primary vector (A), Anopheles secondary 119

32 12

33 Fig 5.9: Simple linear regression between different land use land cover and mosquito collected from survey sites. 121

34 vector (B) and combination of both the vectors (A+B) are taken into consideration. The LULC types, viz. wetlands, marshy lands, river, vegetation, dense forest, agricultural fields, damp areas and sand areas are also considered and one to one correlation between mosquito types and LULC types has been carried out. Results of this analysis are presented in a 8x7 correlation matrix as shown in table 5.3 and figure 5.9. The result of Pearson s correlation between landuse and mosquito types indicates some interesting facts. The wetlands, where water is locked and stable, show positive correlation with all the mosquito species except Culex. The result is significant at.5 level for Anopheles as a whole and also for Anopheles secondary vectors in particular. The Culex mosquito responsible for Japanese encephalitis and Filariasis shows positive correlation with agricultural fields, damp area and sandy area. As malaria is spread by Anopheles, it is, therefore important to know their preferred habitats. The Anopheles show positive correlation with the landuse types such as wetlands, vegetation and dense forest. The dense forest indicates high positive correlation (r = +.725) with Anopheles mosquito which is significant. The primary and the secondary vectors which are responsible for malaria too show significant positive correlation having r = and r = respectively with dense forest. While considering both the vectors, the correlation shows highly positive being r = with dense forest. 122

35 The vegetations grown in and around the villages are abundantly found in all the survey sites. These vegetations show positive correlation, of course at low value of r when Anopheles, Anopheles primary vectors, secondary vectors and both the malaria vectors are taken into consideration (table 5.3). In the table 5.3, the positive correlation with malaria vectors is found with dense forest, vegetation and the wetlands. These are the areas where the vectors carrying malaria are available. The areas like marshy land, river, agricultural fields, damp area and the sandy areas indicate negative correlation thus these are the areas discouraging malaria vectors. But, these are the breeding grounds for another species like Culex and Mansonia. These species are the vectors for other diseases like JE, filariasis, dengue and chikungunya etc. So, it is established from the analysis that the areas, where malaria vector breeds are wetlands, locally available vegetation and dense forest which are the habitats and sites of colonization of malaria vectors. But, the transmission of malaria is primarily dependent upon the presence or existence of parasite within these areas. 123