RESUMO
Background & objectives: Dengue is an arboviral disease of public health importance in many parts of India and recently many cases have been reported from northeastern India. Aedes mosquitoes, which are the vectors of dengue, are widely prevalent in the region. A study was initiated in Sonitpur district of Assam to understand the spatiotemporal distribution and seasonal prevalence of dengue vectors and to identify the high risk zones. Methods: Ovitrap surveys were conducted in three randomly selected villages under each of the eight public health centres (PHC) in district Sonitpur of Assam, northeastern India during March 2011 - February 2012. Three risk zones (high, medium and low) were identified on the basis of per trap density of Aedes mosquitoes. Meteorological data were collected to study the temporal distribution of dengue vectors. Results: Aedes albopictus (99.3%) was the predominant dengue vector followed by Ae. aegypti (0.7%) recorded in the ovitraps. The highest vector density was observed during the post-monsoon (60.1 ± 18 per trap) while the lowest during the winter (7.6 ± 4.9 per trap) and the season-wise differences in the vector density were significant (p=0.005). Maximum temperature (correlation coefficient, r = 0.45) and minimum temperature (r = 0.408) showed the highest positive correlation with the vector density, whereas the number of rainy days showed high positive correlation (r = 0.185) than the total rainfall (r = 0.117). The high risk zone (Dekhiajuli, Behali, Bihaguri and Gohpur PHC) as indicated by the high larval densities of dengue vectors, 45.3 ± 18, 42.1 ± 22.3, 36.9 ± 29.1, 35.3 ± 22.6 per trap, respectively, was validated by dengue epidemiological data collected during 2012. Interpretation & conclusions: Yearlong monitoring of dengue vectors was done for the first time in this region. Monthly maximum temperature and the number of rainy days could be used for the prediction of larval density of Aedes mosquitoes. The identification high dengue risk zones would help in adopting targeted interventions for disease management in future.
RESUMO
Background & objective: Japanese encephalitis (JE) outbreaks are common in Assam, northeastern State of India. Information on resistance in known JE vectors in the affected area is important for effective control measures. This study was undertaken to determine the species abundance of JE vectors endemic to Sibsagar district of Assam, and their susceptibility against DDT and deltamethrin. Methods: Adult mosquitoes were collected using CDC light trap and aspirators from human dwellings from 13 endemic villages falling under three Primary Health Centres. Collected mosquitoes were identified and unfed female mosquitoes were used for DDT and deltamethrin sensitivity bioassay. The bioassay was performed following WHO protocol using standard susceptibility test kit. Knockdown time (KDT) was monitored at every 10 minutes intervals, whereas mortalities were recorded 24 h post-exposure. Vector density and resistance status were mapped using geographic information system (GIS) technique. Results: A total of 7655 mosquitoes were sampled under three genera, i.e. Anopheles, Culex and Mansonia, and nine species, the JE vector Cx. vishnui group (31.78%) was the most predominant species, followed by Ma. uniformis (16.81%) and Ma. indiana (16.45%). All vector species were suspected to be resistant to DDT and sensitive to deltamethrin, except Ma. indiana, which was suspected to deltamethrin resistant. The KDT50 and KDT95 values of vector mosquitoes for DDT were significantly higher as compared to deltamethrin. The probit model used to estimate KDT50 and KDT95 values did not display normal distribution of percentage knockdown with time for all the vectors tested for DDT and deltamethrin, except for Ma. indiana for deltamethrin assay and Cx. gelidus for the DDT assay. Interpretation & conclusion: Differences in insecticide resistance status were observed between insecticides and vector species. The results of this study provided baseline data on insecticide resistance in known JE vectors of Sibsagar, Assam. The maps generated may allow better communication in control operations and comparison of changes in susceptibility status of these vectors over time.
RESUMO
Three sulphur containing compounds, carbon disulphide, dimethyl disulphide and dimethyl sulphide were bioassayed for preference after admixing them in cereal base as ready bait block for use against commensal rat, R. rattus (wild type) in four way choice chamber system. Rat preference for different baits was also studied with automatic recording animal activity meter. Rats exhibited attractancy to the baits at 0.005% concentration of all the three compounds while at 0.01% concentration they have showed repellency. Dimethyl sulphide at 0.005% concentration showed better attractancy towards both sexes of rat.