Transmission Dynamics of Diurnally Subperiodic Lymphatic Filariasis in the Andaman and Nicobar Islands

Abstract

Diurnally subperiodic filariasis (DspWb) is confined to the Nicobar district of Andaman and Nicobar archipelago, India. Point studies have suggested that this type of lymphatic filariasis (LF) is prevalent in the Nancowry group of an archipelago with Downsiomyia nivea as the vector. In-depth studies were undertaken to quantify the transmission dynamics of LF in Nicobar district keeping in perspective its control and assessment of interventions, hitherto not known. Parameters that reflect the dynamics and intensity of transmission, i.e., the annual biting rate (ABR), annual infective biting rate (AIBR), annual transmission index (ATI), risk of infection index (RII), and annual transmission potential (ATP), were estimated. These estimates indicated that a person received 21,851 bites (ABR) of which 107 had harbored infective stage (L3) larvae (AIBR). Each person stood at threat of getting a probable number of 22 L3 larvae per year. Host efficiency index of Do. nivea showed that >40% of the microfilariae ingested developed into L3 stages. ATP indicated perennial transmission. The sequential monthly transmission potential indicated that the force of transmission was high during summer. Persistent transmission of DspWb in the characteristic sylvatic ecology was noticeable with a high risk for transmission during summer. Although personal protection measures are the method of choice for risk reduction, in view of the adult behavior of the vector mosquito and larval ecology, conventional larvicidal measures are not applicable. Alternate methods of reducing the parasite load in the community are discussed in this chapter.