Impact of season on filarial vector density and infection in Raipur City of Chhattisgarh, India.

Background & objectives: Bionomics and transmission dynamics of vector population are profoundly influenced by local climatic conditions. The study monitored variations in density, infection and infectivity rates of Culex quinquefasciatus with respect to season in randomly selected localities of Raipur City of Chhattisgarh state. Methods: The indoor resting density of Cx. quinquefasciatus, Wuchereria bancrofti infection and infectivity rates were monitored in Raipur City at regular monthly intervals for over a period of 12 months and the impact of meteorological conditions on transmission indices were assessed. The frequency distribution of different stages of filarial larvae in naturally infected vector population, host efficiency and transmission intensity index of the vector population was also worked out. Results: The mean vector density of Cx. quinquefasciatus during the study period was 55.22 while the mean vector infection and infectivity rates recorded in Raipur were 4.05 and 0.25% respectively. A gradual increase in Culex infection rate was recorded from June onwards with a maximum (22.14%) in August and minimum (2.38%) in February. No vector with filarial infection was detected during December when the vector density was high. Analysis of frequency distribution of different stages of larvae revealed dominance of microfilarial stage with a mean larval intensity of 5.37. The highest infectivity rate was observed during June (1.15%) and the lowest was in March (0.41%). Both the infection and infectivity rates were at their low during winter season although the density of Cx. quinquefasciatus was at its maximum. Highest mean host efficiency of 0.44 was recorded in February. The annual transmission intensity index (TII) was 32.72. The highest TII was recorded during January and February months. Interpretation & conclusion: The climate appeared to have profound impact on vector density, infection and infectivity rates. The vector infection and infectivity rates were high in rainy season followed by summer and winter seasons. The highest host efficiency was observed in winter followed by summer and rainy seasons. An apparent negative correlation was observed between vector infection rate and vector density. Lower temperatures (23–25oC) with low rainfall favoured progression of mf to L3 in Cx. quinquefasciatus in the study region.

Interruption of Annual Single Dose DEC Regimen Administration : Impact on Wuchereria Bancrofti Microfilaraemia, Vector Infection and Infectivity Rates.

The effect of single dose diethylcarbamazine regimen (6mg/ kg body wt.) in comparison to standard DEC regimen i.e; 72mg/kg body wt (administered in 12 consecutive days) in clearing Wuchereria bancrofti microfilariae from low density micro filariae carriers (1- 8 mf per 20 μl) and its impact on vector infection rate were studied in an urban region endemic for bancroftian filariasis. The efficacy of DEC regimens were determined by assessing the rate of successful treatment, percentage cure rate and percentage decrease in microfilariae count in treated subjects. The 12 days regimen was found very effective with 100% cure rate even after 4 years of drug therapy. In subjects, who received single dose DEC regimen, the rate of successful treatment, cure rate and percent decrease in micro filariae count was significantly low when assessed 24 hour after therapy. Reexamination of subjects in this group at 6, 12, 24 and 48 months after therapy showed a sharp decline in all therapeutic indices and the microfilariae count reached pretreatment levels by 4th year of drug therapy. The single dose regimen had a marginal impact on vector infection and infectivity rates in Culex quinquefasciatus. A marked increase of vector infection and infectivity rates in parallel to human microfilaraemia rate was recorded from the same households when examined after 4th yr after therapy. Thus the single dose 6mg/kg body wt. DEC regimen (administered only once) failed to clear microfilariae even in a situation of filarial low endemicity and did not influence the transmission potential of C. quinquefasciatus.

Population dynamics of Culex quinquefasciatus filaria vector in Raipur City of Chhattisgarh State.

Indoor resting Culex quinquefasciatus were collected from 17 localities of Raipur City using aspirator tube between 06.00 and 08.00 hrs. at monthly intervals for over a period of 12 months. Mosquitoes were also collected using animal and human baits. A total of 4973 C. quinquefasciatus were collected in 176 man hours from different locations of Raipur City with a mean density of 28.26 pmh. The vector was recorded throughout the year with higher densities during the months of March (44.29 pmh), February (41.29 pmh), August (38.58 pmh) and April (37.17 pmh). The lower densities were recorded during July (17.05 pmh), September (16.82 pmh) and November (16.64 pmh). The Gudhyari and Amanaka localities recorded the highest and lowest densities of C. quinquefasciatus respectively. No significant relationship was observed between the density variation of the vector and variation in temperature and/or humidity in the study region.