D. R. Bhattacharyya

Role of the prevalent Anopheles species in the transmission of Plasmodium falciparum and P. vivax in Assam state, north-eastern India.

Abstract In north–eastern India, Anopheles minimus, An. dirus and An. fluviatilis are considered the three major vectors of the parasites causing human malaria. The role in transmission of the other Anopheles species present in this region is not, however, very clear. To examine the vectorial role of the more common anopheline mosquitoes, the heads and thoraces of 4126 female Anopheles belonging to 16 species (collected using miniature light traps set in human dwellings in a foothill village in the Jorhat district of Assam state) were tested, in ELISA, for the circumsporozoite proteins (CSP) of Plasmodium falciparum or the VK-210 and VK-247 polymorphs of P. vivax. Sixty-five pools of head–thorax homogenates, representing 10 different species of Anopheles , were found reactive, giving an overall minimum prevalence of infection (MPI) of 1.58%, with a 95% confidence interval (CI) of 1.21%–2.0%. Among the CSP-reactive pools of mosquitoes, 31% were positive only for P. falciparum, 45% only for P. vivax VK 247, 6% only for P. vivax VK 210, and 18% for both P. falciparum and P. vivax VK 247. The results indicate that not only the proven vector, An. minimus s.l. (MPI = 0.71%), but also several species of Anopheles previously considered unimportant in the epidemiology of malaria, especially An. aconitus (MPI = 3.95%), An. annularis (MPI = 5.8%), the An. hyrcanus group (MPI = 0.48%), An. kochi (MPI = 1.28%), the An. philippinensis-nivipes complex (MPI = 0.94%), and An. vagus (MPI = 3.87%), are important vectors in the foothills of Assam.

Estimation of Vectorial Capacity of Anopheles dirus (Diptera: Culicidae) in a Forest-Fringed Village of Assam (India)

To estimate the vectorial capacity of Anopheles dirus, the main vector of forest malaria in the northeastern region of India, in order to gain an understanding of entomological factors related to malaria transmission in forest-fringe areas of Assam, India, an isolated village in the tropical rain forest-fringed area in the district of Dibrugarh, Assam, under the influence of An. dirus alone was studied. Data on various entomological variables required for computation of the vectorial capacity were generated in each month from June 1999 to May 2000 in the field using standard techniques. Malaria prevalence was also studied during the same period in the study village and correlated with the estimated vectorial capacity of An. dirus. Vectorial capacity of An. dirus was highest, 0.779 for Plasmodium vivax (Pv) and 0.649 for Plasmodium falciparum (Pf), during the hot-monsoon season (June-September) and decreased to 0.08 (Pv) and 0.07(Pf) in the temperate postmonsoon season (October-November) before attaining zero values in the cool-dry season (December-February). With increasing temperature in the temperate premonsoon season (March-May), vectorial capacity recorded was 0.119 and 0.82 for Pv and Pf, respectively. Significant positive correlation was seen between the estimated vectorial capacity of An. dirus and the number of new Pf (r = 0.86, p < 0.001) and Pv (r = 0.69, p < 0.02) cases in the study village in different months. Thus, this study highlights the pattern of malaria transmission by An. dirus in a forest-fringe area of Assam that begins in March, peaks in July/August, subsides by November, and remains interrupted between December and February. Measures for controlling malaria in forest-fringe areas should be scheduled accordingly.

Malaria transmission risk by the mosquito Anopheles baimaii (formerly known as An. dirus species D) at different hours of the night in North-east India.

Abstract.  The risk of acquiring malaria transmitted by Anopheles baimaii Sallum & Peyton, 2005, formerly known as An. dirus species D ( Sallum et al., 2005 ) (Diptera: Culicidae), at different hours of the night in a forest‐fringed village of Assam, North‐east India was assessed through all‐night mosquito landing catches during 1995–2000. An estimated overall mean biting rate of 36.1 bites/person/night (95% CI = 26.2–45.8), a sporozoite rate of 1.9% (95% CI = 1.1–2.9%) and a parous rate of 58.7% (95% CI = 55.3–62.0%) were recorded. Parous and sporozoite‐positive females tended to be caught mainly before midnight. The effective entomological inoculation rate was the highest (0.249 positive bites/person/night) from 21.00 to 24.00 hours, suggesting that the second quartile of the night is the most risky period for malaria transmission by An. baimaii. Considering that ∼21% of mean inoculations take place before 21.00 hours, it appears that there is a need for appropriate protective measures during the pre‐bed time period to supplement the impact of insecticide‐treated nets against An. baimaii in north‐east India.

Spatial distribution and r-DNA second internal transcribed spacer characterization of Anopheles dirus (Diptera: Culicidae) complex species in north-east India.

The identity and distribution of the prevalent member species of the Anopheles dirus complex mosquitoes in the north-eastern region of India was investigated in a cross-sectional study. We altogether collected 267 individuals of An. dirus s.l. from 27 forested/forest fringed locations spread across the seven north-eastern states, identified the species using a ribosomal DNA (r-DNA) second internal transcribed spacer (ITS2) based allele specific polymerase chain reaction (ASPCR) method and sequenced the ITS2 locus in a sub set of mosquitoes. An. baimaii was identified as the main, almost exclusive (266/267), species of the Dirus complex throughout the north-east India with no intraspecific variation in the 479 base pair long ITS2 sequences in 59 of the 60 individuals sequenced. Ribosomal DNA of one individual from Assam state did not amplify in the ASPCR, possessed 786 base pair long ITS2 sequence and showed 99.7% similarity with the sequence of An. dirus species D (An. baimaii) from Yunnan province of China, later referred to as species X of the Dirus complex. These observations suggest the presence of another, possibly the new, species of the Dirus complex, sympatric with An. baimaii, in Assam warranting investigations on its distribution, biology and role in human malaria transmission in north-east India.

Spatial distribution and molecular characterization of Anopheles nivipes and Anopheles philippinensis (Diptera: Culicidae) in north-east India.

Anopheles philippinensis-nivipes species of mosquitoes are considered secondary malaria vectors in the north-east India. However, difficulty in separating An. philippinensis and An. nivipes accurately on the basis of morphological identification, due to the overlapping female wing characters, has led to the paucity of information on their spatial distribution and vectorial importance, essential for understanding malaria disease epidemiology in areas under their influence. In view of this a study was undertaken to generate authentic information on distribution of An. philippinensis and An. nivipes in the north-east India using molecular tools. Between the two, An. nivipes was recorded as the dominant species in Assam, and Nagaland states whereas An. philippinensis was found predominant in the state of Mizoram and Arunachal Pradesh. Species differentiation based on female wing characters proved wrong in about 74% specimens of An. philippinensis but found accurate in case of An. nivipes. No intra-specific variation in second internal transcribed spacer (ITS2) region of ribosomal DNA(r-DNA) in either An. nivipes or An. philippinensis from different geographical areas of north-east India was noted.

Anopheles (Cellia) maculatus group: Its spatial distribution and molecular characterization of member species in north-east India

Anopheles (Cellia) maculatus is considered a group of at least nine formally named species. Faced with the difficulty of correct morphological identification due to overlapping characters, several member species of the An. maculatus group are known to play important role in malaria transmission in the Oriental region. Current assemblage, distribution and vectorial importance of the member species within the Maculatus group is far from clear in the north-eastern region of India. Our study encompassing 410 individuals, collected from 67 geo-referenced spots across the eight north-east Indian states, identified the presence of 6 member species of the Maculatus group using the molecular tools. Anopheles dravidicus and Anopheles rampae were documented for the first time in this part of India with latter forming the new country record. While Anopheles pseudowillmori (59.5%) and An. maculatus (32%) were widely available species in most of the north-eastern states, restricted distribution of Anopheles willmori to Nagaland and that of Anopheles sawadwongporni and An. rampae to Mizoram state was noted. None of the species was found positive for human malaria parasite. While no intraspecific differences existed in the sequences of second internal transcribed spacer (ITS2) region of ribosomal DNA (r-DNA) of the member species of the Maculatus group within north-east India, few differences were detected in the sequences of An. dravidicus, An. maculatus and An. pseudowillmori from north-east India with species from the neighbouring countries.

Acceptability and Practices of Mosquito Bed Net Use Among Hilly Tribes of North-east India

Abstract Twenty six villages, having 1904 households, in five Primary Health Centres of four districts covering seven tribal communities of Arunachal Pradesh and Nagaland states of North-east India were surveyed and information on demography, sleeping habits, pattern and practices related to mosquito bed net use were elicited. Use of bed nets and washing frequency was more pronounced in ethnic tribes of Nagaland. Notes of Arunachal Pradesh were the lowest (65.6 % households) and Angamis of Nagaland were the highest (100 % households) users of bed nets amongst the surveyed communities. Women and children below 15 years of age were more regular users of bed nets in all the communities. Majority, ranging from 93.4 to 96.3%, in Nagaland perceived insecticide treated bed nets better than indoor residual spray. Since mosquito bed nets are, by and large, culturally acceptable in the northeastern region of India and one of the regional malaria mosquito vectors, Anopheles dirus is exophilic, the introduction of ITBNs in tribal areas of North-east India may prove as an useful strategy for malaria control.

Armigeres (Armigeres) Mahantai, A New Mosquito Species from India

Abstract Female and male adults of Armigeres (Armigeres) mahantai, a new mosquito species, are described from Meghalaya state of northeastern India.

ADDITION OF THREE SPECIES OF TOPOMYIA (DIPTERA: CULICIDAE) TO THE MOSQUITO FAUNA OF NORTHEASTERN INDIA

ABSTRACT Topomyia (Topomyia) hirtusa, Topomyia (Topomyia) bifurcata, and Topomyia (Suaymyia) cristata are recorded for the first time in India from the northeastern state of Arunachal Pradesh.

Microwave assisted synthesis, antimalarial screening and structure–activity-relationship exploration of some phenylthiazolyl-triazine derivatives against dihydrofolate reductase

In this study, a microwave-assisted methodology was first attempted to facilitate the synthesis of hybrid phenylthiazolyl-triazine derivatives. These two nuclei were clubbed together based on the structural requirement of existing antimalarial antifolates. A comparative analysis revealed that compounds synthesized using microwave-assisted procedure gave better yield and minimized the reaction time with respect to the conventional procedure. Hybrid compounds were screened for their in vitro antimalarial activity against chloroquine-sensitive (3D-7) strain of Plasmodium falciparum at 5 µg/mL and 50 µg/mL dose level. An insight into the structure–activity-relationship of the synthesized compounds was gained by docking them in the crystal structure of wild type Plasmodium falciparum dihydrofolate reductase-thymidylate synthase.