Dynamics of Malaria Transmission in Forested and Deforested Regions of Mandla District, Central India (Madhya Pradesh)
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Journal of the American Mosquito Control Association, 12(2):225-234' 1996 Copyright @ 1996 by the American Mosquito Control Association, Inc. DYNAMICS OF MALARIA TRANSMISSION IN FORESTED AND DEFORESTED REGIONS OF MANDLA DISTRICT, CENTRAL INDIA (MADHYA PRADESH) NEERU SINGH,' O. P SINGH' nNo V. P. SHARMA' ABSTRACT. A longitudinal malaria study was undertaken in 1990-91 in 2 adjacent ecological zones in central India: villages in forest and villages away from the forest. The prevalence of Anopheles species varied widely between the 2 ecological settings. In the villages in forest, Anopheles culicifacies and An. was predom- fluviatitis were mainly exophilic, whereas in the viltages away from forest, An. culicifacies inantly endophilic and An. fluviatilis was equally prevalent both indoors and outdoors. The seasonal patterns of malaria transmission were also different between the 2 zones. Plasmodium falciparum was ihe dominant parasite species in the villages in forest, whereas malaria infection was mainly due to Plasmodium vivax in the villages away from forest. The annual parasite incidence was high in the villages in forest. The failure to control malaria in forested areas is rooted in the terrain and a variety of poorly understood sociological factors. INTRODUCTION in forested areas. Therefore, we initiated an ep- idemiologic study in villages in the forested ar- with an area Madhya Pradesh in central India, eas compared to villages in deforested areas to in India. The of 442,841 km2, is the largest state investigate the factors responsible for the differ- state has a total population of 52.2 million, out ences in malaria prevalence. of which 12 million are classed as tribal people (the highest number of tribals in the country). Forest covers 330,828 km2 (757o) and is a res- MATERIALS AND METHODS perennial ervoir of intense malaria transmission. Mandla (23'N, 80'10'E) is a tribal district. in 1987, mil- According to an estimate made 54 The villages are broadly classified into 2 types: lion tribals of various ethnic origins residing in interior reserve forest villages (> 600 m eleva- forested areas and accounting forTVo ofthe total tion) and roadside, revenue villages, 15 km population of India contributed 3OVoof the total away from forest (( 500 m elevation). Six vil- malaria cases, 6OVo each of total Plasmodium lages were selected (Fig. l), 4 from the forests falciparum cases and total malaria deaths in the (site l) and 2 from the roadsides (site 2). All 6 (Narasimham resis- country 1991). Chloroquine villages were sprayed with 2 rounds of DDT in tance in P. is a common feature falciparum May and July by the National Malaria Eradica- (Ghosh et al. 1989, Singh et al. 1989b). Two tion Programme (NMEP). There are 3 seasons: species occur in area, Anopheles cul- vector the hot (March-June), rainy (July-October), and icifacies Giles and An. James (Kalra fluviarilis cold (November-February). Climatic data are prevalent 1978, Kulkarni 1987), which are presented in Table l. throughout the year (Singh et al. 1989a). Recent Site l: This group of 4 villages (807o Gond in Mandla have shown that studies the district tribals) is located in dense forest. The villages An. culicifocies is a complex of 4 sibling species are sparsely populated (lOO-300 inhabitants per designated A, B, C, and D, with species C com- village). They are 15-25 km from the main road prising 8O-9OVo of the individuals collected and inaccessible for at least 4 months per year (Subbarao et al. 1992). The subspecies status of during rainy periods. Several seasonal and pe- An. is not known. fluviatilis rennial streams crisscross the villages. The entire The Mandla district in the center of Madhya area is infested by snakes, scorpions, and spiders Pradesh is a region of broad valleys, hills, and during the rains. The tropical moist, deciduous rocky undulating terrain with thick dense forests forest of the area consists mostly of Tectona at altitudes of 450-950 m. Although the large grandis (teak), Shorea robusta (sal), Madhuca forests are preserved, virtually all the villages indica (mahta), and Bambusa nutanus (bam- state highway have long along the been cleared boo). There are no schools or health centers in of forest. During routine epidemiologic surveys these villages and people are mostly illiterate, more malaria cases were recorded from villaees scantily clothed, and work mainly in forest nurs- eries. Their houses, which are scattered in agri- ' Malaria Research Centre, Field Station, Medical cultural fields and forest. are made of mud. College, Jabalpuq M.P., India. thatch, and bamboo. The houses are small with 'Malaria Research Centre, 22-Sham Nath Marg, low doors and windows. Fewer than 2O7o have Delhi, India. electricity (only one point connection per dwell- 225 Jotmar- oF THE AMERTcANMoseurro Coxrnol AssocrarroN Vol. 12, No. 2 h$ A INOEX 9 VILLAGEsAWAY FROHFOREST O VILLAGESIN FOREST E PRIMARYHEALTH CENTRE 59 KM ffi Fig. l. A. Map of India showing the location of Madhya Pradesh and the Mandla district. B. Bizadandi Primary Health Centre, showing study villages. ing). Very often cattle are also sheltered in the Mosquito sampling: Indoor resting mosqui- houses. Drinking water is brought from wells or toes (per man-hour) were collected twice per seepages. month for 4 consecutive days from 4 villages (2 Si/e 2.' These 2 villages are densely populated from each site) for I year (1990-91). Anophe- (6OVo Gond tribals) and relatively prosperous. lines resting inside 4 fixed (the same structures Residents seldom work away from the villages. were sampled each time) houses located in dif- Two medical officers stay at the Primary Health ferent parts of the villages (2 human dwellings Centre (PHC), about 0.5 km from Bizadandi vil- and 2 cattle sheds) were sampled during the ear- lage. The other village, Dhanwahi, is about 5 km ly morning (0600 h) for 15 min at each place. away from the PHC. Houses are better ventilat- A team of 2 insect collectors was assigned to ed, have electricity, and are made of brick and each village. The same collectors caught mos- mud with tiled roofs. There are numerous fresh quitoes with flashlights and mouth aspirators at water springs, seepages, and pools along the each study village (24 collections). After indoor shallow streams during rains. resting collections were made, anophelines rest- Table 1. Rainfall in villaees of the Mandla district.' Year 1990 r991 Total Total Temperature Humidity Temperature Humidity rain- Rainy rain- Rainy fall days Max. Min. Max. Minl fall days Max. Min. Max. Min. Villages (mm) (No.) ('C) (Vo) (mm) (No.) cc) (vo) Away from 1,766.5 74 42.3 7.7 90 25 t,302.2 53 44.4 3.9 88 20 forest In forest 2,077.3 82 4r.5 3.5 98 45 r,452.5 72 44.6 0.5 95 40 I Measurements re from the Meteorological Depiltment, Nagpur Jws 1996 Meunre T[ANsMIssIoN rN Csvrner INore 227 Thble 2. Mean indoor resting density (per man-hour) of anophelines in villages of Bizadandi, rn the Mandla district. Villages in forest Villages away from forest All An. An. All An. An. Month Anopheles culicifacies fluviatilis Anopheles culicifacies fluviatilis Jan. 18.0 9.5 1.4 32.8 26.5 0.5 Feb. 7.O 2.O 1.0 27.3 22.5 0.0 March 7.O 2.O 0.8 15.0 12.o 0.0 April 1.0 1.0 0.0 13.5 9.3 0.0 Mayt 0.0 0.0 0.0 5.0 4.O 0.0 June l.o l.o 0.0 7.5 5.5 0.0 July' 40.5 36.0 0.8 44.5 31.5 0.0 Aug. 80.0 70.5 0.5 51.5 34.3 0.0 Sept. 53.0 42.5 0.5 62.5 31.5 1.5 Oct. ) /.) 36.5 3.5 68.0 28.8 2.O Nov. 30.0 21.5 2.5 61.0 26.5 2.O Dec. 16.5 15.0 1.0 32.O 15.5 2.O Total 311.5 237.5 t2.o 420.6 247.9 8.0 'DDT sprayed, fist romd in May and seond round in July ing outdoors were collected by the same team Mosquitoes were identified in the laboratory of 2 collectors for 2 h from stone quarries, bush- using standard keys (Christophers 1933, Puri es, small plants near streams, on fences, and 1955, Wattal and Kalra 1961). Only An. culici- from tree holes. etc. facies and An. fluviatilis were dissected for the Although human biting catches were planned presence of sporozoites in salivary glands, as the once each month in these 4 villages, human bait remaining species were only abundant during catches were terminated due to many operational limited periods of the year. Further, because both difficulties.3 An altemative sampling method, An. culicifacies and An. fluviatilis comprise sib- CDC light trapping, was used once a month for ling species, and separation of these sibling spe- 4 consecutive nights for I year. The traps were cies require cytogenetic studies, we decided to run for a period of 48 nights (12 nights at each lump these species rather than risk errors in sort- village) from 1800 to O6O0 h. Traps were always ing under primitive field conditions. placed at a constant height of 5.5 ft., at fixed Malaria surveillance: Blood smears were locations, outdoors near occupied human dwell- prepared twice a month from all fever cases and ings and indoors in human dwellings (12 outside people with fever during the preceding 14 days and 12 inside in each village). Each trap was (active case detection).