Search

Weather and anthropogenic factors are important determinants for Japanese encephalitis (JE) transmission. During 2008-2010, an increasing trend of JE was observed in Dibrugarh district of Northeast India. The JE cases were found to be clustered between June to October in each year. Monthly minimum temperature and rainfall were significantly associated with JE transmission at 1 and 2 months lagged. However, the relationship was more prominent at a lag of 1 month than that of two. Regression analysis suggested that rainfall, minimum and maximum temperature, and relative humidity at 6:00 h are significant predictors (P < 0.05) of quarterly occurrence of JE cases. Additional anthropogenic risk factors including the conditions such as pig sty/cattle shed around and lower part of the houses and proximity of rice field to the dwelling houses (P < 0.05) were also found to be predictors for JE occurrence. Meteorological and anthropogenic risk factors can be used to forecast JE outbreaks in Assam which in turn can help the local health authorities to protect communities in JE prone areas.

A study on mosquitoes in parts of Meghalaya revealed the presence of 64 species of mosquitoes under 10 genera. In monsoon (June to October) and post-monsoon (November to May) survey, 42 and 48 species of mosquitoes were detected, respectivily. Higher species diversity was found at lower elevations (up to 1050 m). Anopheles peditaeniatus, An. sinensis, Aedes vexans, Ae. nigrostriatus, Ae. annandalei, Culex. fuscocephala, Cx. pseudovishnui, Cx. murrelli, Cx. brevipalpis, Coquillettidia novochracea, Lutzia halifaxii, Malaya genurostris, Ml. jacobsoni, Tripteroides aranoides, Toxorhynchites minimus, Uranotaenia campestris, Ur. edwardsi and Ur. testaceae which were never reported earlier from Meghalaya state were detected in the present study and the findings were discussed with previously published reports from the state.

A temporal relationship of Japanese encephalitis virus (JEV) transmission in pigs, mosquitoes and humans revealed that sentinel pig seroconversions were significantly associated with human cases 4 weeks before (P = 0·04) their occurrence, highly correlated during the same time and 2 weeks before case occurrence (P < 0·001), and remained significantly correlated up to 2 weeks after human case occurrence (P < 0·01). JEV was detected in the same month in pigs and mosquitoes, and peaks of pig seroconversion were preceded by 1-2 months of peaks of infection in vectors. Kaplan-Meier analysis indicated that detection of JEV-positive mosquitoes was significantly associated with the median time to occurrence of seroconversion in pigs (P < 0·05). This study will not only help in predicting JEV activity but also accelerate timely vector control measures and vaccination programmes for pigs and humans to reduce the Japanese encephalitis risk in endemic areas.

Entomological surveys were conducted for three consecutive years in core and buffer zone of the Dibru-Saikhowa biosphere reserve in pre monsoon, monsoon and post-monsoon seasons. A total of 52 species of mosquitoes under eleven genera have been detected. The genus Anopheles (18 species) was the predominant followed by Culex, Aedes, Mansonia, Armigeres, Mimomyia, Ochlerostatus, Malaya, Toxorhynchites, Ficalbia and Aedeomyia. The buffer zone of the forest reserve where human habitations are there exhibited the presence of maximum number of species (49 species under 10 genera) in comparison to core zone (42 species under 10 genera). In buffer zone, maximum numbers of species (38) were recorded in monsoon season followed by post- monsoon (35 species) and Pre-monsoon season (34 species). Whereas in core zone, maximum number of species were collected in post monsoon season followed by pre monsoon season and monsoon season. In Core and buffer zone, the maximum species were recorded from the ground pool habitat and slow flowing stream respectively. Among the disease vectors, the potential Japanese encephalitis vectors incriminated in India were very much prevalent. This study provides the list of available mosquito species recorded for the first time in the Dibru-Saikhowa biosphere reserve.

A mosquito faunistic survey conducted during 1999-2005 in 7 different states of the northeastern (NE) region of India revealed that the region is very rich in mosquito fauna, particularly of the genus Aedes. From the present survey and earlier published reports, a total of 48 species of Aedes and a related genus Verrallina were recorded. The state of Assam contributed the highest number of species compared to the other 6 states, namely Arunachal Pradesh, Manipur, Meghalaya, Mizoram, Nagaland, and Tripura. Larvae of 46 species were collected from 16 different habitats and for some species the habitats were species specific. The known dengue vectors, Aedes aegypti and Ae. albopictus, were recorded from all 7 states, although Ae. aegypti was not known earlier from Mizoram, Nagaland, and Tripura states. Aedes albotaeniatus was a new addition to the Aedes fauna of the region.

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.

Entomological studies conducted during monsoon and post-monsoon season in Manipur State revealed the presence of fifty-five species of mosquitoes under ten genera. Out of the seventeen Anopheles species recorded, Anopheles aconitus, An. dirus and An. nivipes were recorded for the first time from the state. The present study has confirmed the existence of An. dirus, the major malaria vector in the Northeast from a selected area of the state. Among Culicines, four species viz., Aedes nigrostriatus, Malaya genurostris, Aediomyia catasticta and Toxorhynchites splendens which were not reported earlier from this state have been recorded in the present study. With the addition of these seven species of mosquitoes to the earlier record of mosquitoes so far reported from Manipur, the mosquito fauna swells up to one hundred and eleven including the major vectors of malaria of the Northeast and the potential vectors of Japanese encephalitis and dengue virus transmission in India.

The adult female, adult male, pupa, and larva of Uranotaenia (Pseudoficalbia) dibrugarhensis, new species, are described from the Dibrugarh District of Assam State, India.

Culex (Lophoceraomyia) quadripalpis is recorded for the 1st time in India. Collections of Culex (Lophoceraomyia) mammilifer and Uranotaenia (Pseudoficalbia) novobscura are new records from Assam in northeastern India.

In an entomological study, covering three biotopes like village, panikheti (wet rice cultivated land) and urban agglomeration, a total of 35 species of mosquitoes in eight genera were recorded in Jairampur area of Arunachal Pradesh. Two mosquito species--Orthopodomyia anopheloides and Tripteroides indicus were recorded for the first time in Arunachal Pradesh. Anopheles dirus and An. minimus, the two well-known malaria vectors were encountered in the study along with several potential vector species like An. annularis, An. culicifacies, An. maculatus group and An. philippinensis/nivipes. The diversity of mosquito species as well as the man-vector contact was maximum in the panikheti and minimum in the village biotope.

In an entomological study in South Tripura district of Tripura state during June 1998, a total of 31 species of mosquitoes belonging to eight genera were recorded. Among the known malaria vectors in India, Anopheles annularis, An. jeyporiensis, An. minimus, An. philippinensis/nivipes and An. varuna were collected but none of them could be incriminated. During the survey, Aedes pallidostriatus and Malaya genurostris were recorded for the first time in the north-eastern region and Tripura state respectively. Presence of host seeking An. minimus in light-trap collections indoors and its absence during morning indoor resting collections indicated the probability of some degree of exophilic behaviour of An. minimus population in Tripura.

Ninety-one mosquito species in 15 genera were collected from 22 habitat types of Upper Brahmaputra valley in Assam and bordering areas of Arunachal Pradesh. Nineteen species have been recorded for the first time in Assam including seven first records from the northeast region and three first country records. Jaccard's coefficient was used to quantify the similarity between 13 different geographical localities surveyed on the basis of their mosquito fauna. Group average sorting (UPGMA) cluster analysis was used to find out relationship between Jonai, Dhemaji, Dibrugarh, Tinsukia and north Lakhimpur (study zones) on the basis of their mosquito community. Immatures of three malaria vectors incriminated from the northeast India, viz. Anopheles dirus, An. minimus and An. philippinensis were collected exclusively from forest areas. Fourteen potential vectors of Japanese encephalitis incriminated from elsewhere in India were collected during the study.

Culex (Lophoceraomyia) peytoni Bram and Rattanarithikul is recorded for the first time from mainland India and Heizmannia (Heizmannia) reidi Mattingly for the first time from Assam, in northeast India.

Temporal changes in the abundance of host-seeking, potential Japanese encephalitis (JE) vector mosquitos and the role of some ecological factors that are modulating the abundance of vector mosquitos were studied. Vector surveillance was conducted for one year in 4 JE prone villages of Dibrugarh, Assam. Among potential JE vectors, the most abundant mosquito was Culex vishnui s.s. comprising about 22.32%. Maximum density of the mosquito was found during the month of April and another peak was observed in the month of September. The influence of meteorological factors on the abundance of JE vectors was found to vary from species to species. The final multiple regression equations (after variables were selected using STEPWISE procedure) consisted of a combination of linear, quadratic, cubic and interactive ecological variables and accounted for 25-98% of the variations in the abundance of JE vector mosquitos. Complex interactions among environmental factors, such as minimum and maximum temperature, rainfall and flood level are involved in modulating the seasonal abundance of mosquitos. A time lag is involved before a cause and effect relationship is established between environmental parameters (independent variables) and entomological variables (dependent variables). Inundation caused by flooding is favorable for mansonioid mosquito species whereas it has an adverse effect on non-mansonioid mosquito species.