Elimination of lymphatic filariasis as a public health problem from Tonga

Background: Tonga was highly endemic for lymphatic filariasis (LF) caused by diurnally sub-periodic Wuchereria bancrofti transmitted by Aedes vector species. LF prevalence declined very appreciably as a result of chemotherapeutic intervention measures implemented in 1977, but low levels of infection persisted. Along with other Pacific Island countries and in partnership with the Pacific Programme to Eliminate LF (PacELF), Tonga implemented a programme to eliminate LF as a public health problem.
Methods: On the basis of historical data and baseline survey, all the divisions of the country were declared as endemic. Five to six consecutive rounds of effective MDA were implemented in all the divisions during 2001–2006. The impact of MDA was assessed through interim and post-MDA antigen (Ag) detection surveys among adults and transmission assessment surveys among children. The chronic disease burden was assessed by health workers through observation.
Results: The base-line Ag prevalence was 2.70%. The treatment coverage was > 80% in all MDA rounds. The midterm surveys
showed an Ag prevalence of 2.46%. The pre-stop MDA Ag survey revealed an Ag prevalence of 0.34%.The stop MDA survey and transmission assessment surveys among children showed Ag prevalence at < 0.05%,indicating transmission is negligible. Health workers concluded that filarial lymphedema or hydrocele condition in the communities is absent or very rare.
Conclusion: Tonga had successfully met the criteria for elimination of LF as a public health problem. The accomplishment was acknowledged by the WHO in 2017. Tonga looks forward to work with stakeholders to eliminate transmission of LF and achieve zero incidence of infection.