A Different Perspective on Global Mapping of Lymphatic Filariasis

Abstract

In the article on Global Mapping of Lymphatic Filariasis by E. Michael and D.A.P. Bundy[1xMichael, E. and Bundy, D.A.P. Parasitol. Today. 1997; 13: 472–476Abstract | Full Text PDF | PubMed | Scopus (179)See all References[1], the impression is given that the highest regional prevalence for filariasis occurs in the Pacific Islands, with the three highest prevalence rates in the world apparently occurring in Tonga (48%), Papua New Guinea (39%) and the Cook Islands (39%). The authors point out that these conclusions are based on old data, collected mainly between 1950 and 1960. I provide information below to show a different perspective.The reports of the WHO Expert Committees on Filariasis that met in Geneva in December 1983 and October 1991 mentioned that 10.9 million and 3.9 million persons, respectively, had overt filariasis infection in the West Pacific Region. The prevalence based on the population living in the endemic areas was 2.9% for both reporting periods. This marked reduction in total number of cases is undoubtedly due to the achievements made in China, where (currently) less than one million cases occur; at one time, there were reports of 30 million cases.The Pacific Islands also have participated in successful filariasis control campaigns. Based on reports of the WHO/South Pacific Commission Joint Seminar on Filariasis and Vector Control held in Apia, Samoa in 1974 and the WHO Working Group on Subperiodic Wuchereria bancrofti Filariasis held in Apia in 1978, and various WHO staff assignment and consultant reports, multiple dose mass drug administration (MDA) with diethylcarbamazine (DEC) had reduced the prevalence of filariasis in American Samoa from 21% to 0.27%; Samoa (formerly called Western Samoa) from 19.1% to 0.24%; Tonga from 20.4% to 1.6%; French Polynesia from 30% to 0.3%; Aitukaki Island on Cook Islands from 30% to 0.8%; and Fiji from 15% to 1%.MDAs were also carried out in Niue and Tuvalu, where post-treatment results are not readily available. A 1977 survey on Mitiaro Island (273 persons) on Cook Islands revealed a microfilaria prevalence of 30%, where treatment had not been carried out. Prevalences below 1% will rise unless MDAs are repeated, but it is not practical to do them every year. For example, the prevalence in Samoa once had returned to 5%. However, the traditional clinical symptoms of filariasis are disappearing in Samoa and the other Pacific Island countries and areas.In the Pacific Islands where malaria and filariasis overlap, the natural decline and eradication of Wuchereria bancrofti in the Solomon Islands during the 1970s is well documented. This was entirely due to the large-scale malaria vector control operations using DDT indoor residual sprays, where the microfilaria rates dropped from 20% to zero.The large-scale vector control operations now taking place in Vanuatu for malaria control are likely to help keep filariasis controlled. From a regional perspective, the greatest need is in Papua New Guinea, where high filariasis prevalence undoubtedly occurs in certain areas. Certainly more efforts are needed there, not only for malaria, but also for filariasis control.Governments in the Pacific at this time continue to give importance to filariasis surveillance and control. Activities are limited on the basis of available resources. However, significant public health achievements have been made and several countries were pioneers (French Polynesia, Samoa, Fiji) in successfully introducing the single annual mass (DEC) drug treatments, many years before others. It is now recognized that one single annual treatment is only slightly less effective than the multiple 12-day treatment course, which is more difficult to administer. The region is planning to introduce the new combined drug therapy (DEC and ivermectin) and has formulated criteria for achieving the status of filariasis elimination. In 1996, Samoa was the first country in the world to use the new combined therapy on a country-wide basis, where the filariasis prevalence is now about 1%. A second combined MDA is planned this year. The Pacific Islands will continue to strive to maintain, strengthen and expand their surveillance and control efforts.