Estimation of permissible levels of transmission of bancroftian filariasis based on some entomological and parasitological results of a 5-year vector control programme.

The impact of a 5-year vector control programme on transmission of bancroftian filariasis and microfilaraemia levels in the human population was examined in Pondicherry, South India. The programme reduced and maintained the transmission of Wuchereria bancrofti at appreciably low levels in many localities of Pondicherry town, but its impact on overall microfilaraemia prevalence was only limited. However, prevalence of infection was reduced drastically in children born after establishment of the programme and only 18% of the number expected without vector control were found infected. No new infections were found in localities with less transmission intensity. It is proposed that a Transmission Intensity Index of 0.50 and Annual Transmission Potential of less than the 96-105 range are permissible levels of transmission, and below these levels no new infections may occur. The required duration of vector control to eliminate Culex-borne filariasis foci is estimated to be 11-12 years, slightly longer than that required to eradicate anopheline-borne filariasis.