Showing papers by "P. K. Das published in 2002"
TL;DR: It is concluded that geostatistic methods can provide a powerful framework for carrying out the empirical investigation and analysis of parasite spatial population structure and that their successful application will crucially depend on gaining a more thorough understanding of the appropriate geographic scales at which spatial studies should be carried out.
Abstract: Gaining a better understanding of the spatial population structure of infectious agents is increasingly recognized as being key to their more effective mapping and to improving knowledge of their overall population dynamics and control. Here, we investigate the spatial structure of bancroftian filariasis distribution using geostatistical methods in an endemic region in Southern India. Analysis of a parasite antigenemia prevalence dataset assembled by sampling 79 villages selected using a World Health Organization (WHO) proposed 25 x 25 km grid sampling procedure in a 225 x 225 km area within this region was compared with that of a corresponding microfilaraemia prevalence dataset assembled by sampling 119 randomly selected villages from a smaller subregion located within the main study area. A major finding from the analysis was that once large-scale spatial trends were removed, the antigenemia data did not show evidence for the existence of any small-scale dependency at the study sampling interval of 25 km. By contrast, analysis of the randomly sampled microfilaraemia data indicated strong spatial contagion in prevalence up to a distance of approximately 6.6 kms, suggesting the likely existence of small spatial patches or foci of transmission in the study area occurring below the sampling scale used for sampling the antigenemia data. While this could indicate differences in parasite spatial population dynamics based on antigenemia versus microfilaraemia data, the result may also suggest that the WHO recommended 25 x 25 km sampling grid for rapid filariasis mapping could have been too coarse a scale to capture and describe the likely local variation in filariasis infection in this endemic location and highlights the need for caution when applying uniform sampling schemes in diverse endemic regions for investigating the spatial pattern of this parasitic infection. The present results, on the other hand, imply that both small-scale spatial processes and large-scale factors may characterize the observed distribution of filariasis in the study region. Our preliminary analysis of a mountain range associated large-scale trend in the antigenemia data suggested that a nonlinear relationship of infection prevalence with elevation might be a factor behind such observed global spatial patterns. We conclude that geostatistic methods can provide a powerful framework for carrying out the empirical investigation and analysis of parasite spatial population structure. This study shows that their successful application, however, will crucially depend on our gaining a more thorough understanding of the appropriate geographic scales at which spatial studies should be carried out.
67 citations
TL;DR: Results from this and other recent operational studies proved that single‐dose treatment with antifilarials is very effective at community level, feasible, logistically easier and cheap and hence a highly appropriate strategy to control or eliminate LF.
Abstract: Annual mass treatment with single-dose diethylcarbamazine (DEC) or ivermectin (IVM) in combination with albendazole (ALB) for 4-6 years is the principal tool of lymphatic filariasis (LF) elimination strategy. This placebo-controlled study examined the potential of six rounds of mass treatment with DEC or IVM to eliminate Wuchereria bancrofti infection in humans in rural areas in South India. A percentage of 54-75 of the eligible population (>or= 15 kg body weight) received treatment during different rounds of treatment--27.4% in the DEC arm and 30.7% in the IVM arm received all six treatments 4.8% and 5.6% received none and the remainder received 1-5 treatments. After six cycles of treatment the microfilaria (Mf) prevalence in treated communities dropped by 86% in the DEC arm (P 50Mf/60 cu. mm of blood) carriers was reduced by 94% (P < 0.01) in the DEC arm and by 90% (P < 0.01) in the IVM arm. Among those who received all six treatments 1.4% in the DEC arm and 2.4% in the IVM arm remained positive for Mf. Two of five villages in the DEC arm and one of five in the IVM arm showed zero Mf prevalence but continued to have low levels of transmission of infection. The results also indicate that DEC is as effective as or slightly better than IVM against microfilaremia. Results from this and other recent operational studies proved that single-dose treatment with antifilarials is very effective at community level feasible logistically easier and cheap and hence a highly appropriate strategy to control of eliminate LF. Higher treatment coverage than that observed in this study and a few more than six cycles of treatment and more effective treatment tools/strategies may be necessary to reduce microfilaremia to zero level in all communities which may lead to elimination of LF. (authors)
45 citations