Spatial and temporal variations in prevalence, intensity and aggregation of microfilaria in the human host.

The prevalence, intensity and the frequency distribution of microfilaria (mf) of Wuchereria bancrofti in the human blood and their variation in time (pre-vector control, control and post control periods) and space have been examined. The prevalence and intensity showed significant variation between time and different areas of urban Pondicherry. The significant reduction in the prevalence and intensity of microfilaremia in the areas of high endemicity indicated that the effect of vector control was well marked in these areas. The distribution of microfilaria in human population was adequately described by the truncated negative binomial prior to interruption of transmission, and the dispersion parameter 'k' of the negative binomial varied between 0.17 and 0.68. A change in the distribution was observed after the 5 years of vector control, during which the transmission was completely interrupted. The increased 'k' values suggest that the distribution of mf is influenced by the degree of exposure to infection. Therefore, comparison of changes in the parameter 'k' can be considered as an additional tool for evaluating the control operations aimed at interrupting the transmission.