Impact of the 2004 mass drug administration for the control of lymphatic filariasis, in urban and rural areas of the Western province of Sri Lanka

Lymphatic filariasis is targeted to be eliminated globally, at least as a public-health problem, by 2020. The comprehensive strategy for achieving this goal includes the interruption of the transmission of the causative parasites, by drastically reducing the prevalences of microfilaraemia in at-risk communities. In a descriptive, comparative, cross-sectional and community-based study, the impact of the 2004 mass drug administration (MDA) on filarial infection, in selected areas of the Western province of Sri Lanka, has now been assessed 1-2 and 11 months after the administration of the diethylcarbamazine-albendazole combination employed. Using the cluster-sampling method, urban study populations were selected in the Colombo districts and rural ones were selected in the Gampaha district. After obtaining informed written consent, 2 ml venous blood were collected, between 20.00 and 24.00 hours, from each subject. Personal details and drug compliance in the 2004 MDA were recorded. The samples of 'night' blood were checked for microfilariae, using membrane filtration, and for filarial antigenaemia, using commercial (NOWH) immunochromatographic test kits. Eighty-four (4.10%) of the 2034 subjects examined 1-2 months after the 2004 MDA but only four (0.20%) of the 1974 subjects checked 11 months after the MDA were found antigenaemic and/or microfilaraemic (P < 0.001). Between the two follow-ups, the overall prevalences of both antigenaemia (4.03% v. 0.15%; P < 0.001) and microfilaraemia (0.20% v. 0.05%; P=0.38) fell, although only the reduction in antigenaemia was statistically significant. The prevalence of infection ( as indicated by antigenaemia and/or microfilaraemia) fell significantly within each of the two study districts (P < 0.001). Although, when the prevalence of infection was high, drug compliance appeared to be an important determinant of the reduction of antigenaemia (P < 0.04), the 20% difference in compliance between urban and rural areas had no apparent effect on the corresponding prevalences of infection recorded at either follow-up.