Trend of Wuchereria bancrofti infection in Pondicherry urban agglomeration after the withdrawal of a five year vector control programme.

A study was undertaken to investigate the changes in the prevalence of bancroftian filariasis after six years of withdrawal of a five year (1981-85) vector control programme in Pondicherry and the results are presented in this paper. Though there was a drastic increase in the intensity of transmission of filariasis after the withdrawal of vector control operations in 1986, the prevalence of microfilaria (mf rate) of the population declined from 6.35% in 1986 to 4.80% in 1992 (P < 0.05). However, there was an appreciable increase in the mf rate and intensity in the children (0.5 year) born after the withdrawal of the control operations. The overall loss rate of infection was much higher than the gain rate. Many people found to be microfilaraemic six years before, became amicrofilaraemic now. The overall reduction in mf rate, higher loss rate of infection and microfilaraemic people turning amicrofilaraemic indicate that chemotherapy, which has been intensified during the last five years under the National Filaria Control Programme (NFCP), was playing a major role in reducing the infection. However, implementation of mass chemotherapy with annual single dose of DEC (6 mg/kg), combined with vector control may yield better results in further reducing the mf rate as the current approach of detection for treatment may become increasingly difficult with gradual fall in endemicity level. Mass chemotherapy will provide an opportunity to further reduce the mf rate and eliminate filariasis within a few years from Pondicherry urban agglomeration. The increase in the incidence of infection in children, born after the withdrawal of the vector control programme clearly indicates that transmission is continuing and if immediate action is not undertaken it would be difficult to sustain the gains.