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Background: Antibody (Ab) to the Wuchereria bancrofti (Wb) infective larval (L3) antigen Wb123, using a Luciferase Immunoprecipitation System (LIPS) assay, has been shown to be a species-specific, early marker of infection developed for potential use as a surveillance tool following transmission interruption post mass drug administration. To examine its usefulness in a single filarial-endemic island assessed at two time points with markedly different levels of transmission, Ab to Wb123 was measured in sera collected from subjects from Mauke, Cook Islands in 1975 (no previous treatment) and 1992 (5 years after a one time island-wide treatment with diethylcarbamazine [DEC])., Findings: Between 1975 and 1992, Wb transmission decreased dramatically as evidenced by reduced prevalences of microfilariae (31% vs. 5%) and circulating Ag (CAg, 49% vs. 16%). Age specific prevalence analysis showed a dramatic reduction in Wb123 Ab positivity from 54% (25/46) in 1975 to 8% (3/38) in 1992 in children 1-5 years (p<0.0001), reflecting the effects of single-dose treatment five years earlier. By 1992, Wb123 Ab prevalence in children 6-10 years had fallen from 75% (42/56) in 1975 to 42% (33/79) consistent with a lower cumulative transmission potential. In the whole population, Wb123 seropositivity decreased from 86% to 60% between 1975 and 1992. In CAg+ subjects the levels of Wb123 Ab were indistinguishable between the 2 time points but differed in those who were CAg- (p<0.0001). In paired sample analysis, individuals who were CAg+ in 1975 but became CAg- in 1992 had significantly lower Ab levels in 1992 (p<0.0001), with 9/40 (23%) becoming seronegative for Wb123., Conclusions: The relationship between reduction in Wb123 Ab prevalence and the reduction of transmission, seen most clearly in young children, strongly advocates for the continuing assessment and rapid development of Wb123 as a surveillance tool to detect potential transmission of bancroftian filariasis in treated endemic areas.

Circulating filarial antigen (CFA), determined with Og4C3 ELISA, is a marker of Wuchereria bancrofti adult worm infection. The reduction of CFA over 2 years was determined in 185 microfilaremic and 111 amicrofilaremic but CFA+ adults given an annual dose of either diethylcarbamazine (DEC) or ivermectin or the two combined. Reduction of CFA level was good with DEC but weak with ivermectin and followed the same pattern in amicrofilaremic and microfilaremic groups. Combinations and DEC alone had a similar impact on CFA level. CFA clearance was observed in amicrofilaremic but not in microfilaremic persons in all DEC-containing treatments. However, the highest clearance rate was observed in persons treated with DEC at 6 mg/kg combined with ivermectin. Continuous reduction of CFA level after repeated treatments shows that elimination of W. bancrofti infection, monitored by CFA clearance, might be achieved within a few years with annual treatments of DEC combined with ivermectin.

The authors assess of three decades of struggle against Bancroftian filariasis in French Polynesia. Wuchereria bancrofti var. pacifica, aperiodic filaria, and Aedes polynesiensis, mosquito with high parasitologic output, set up a cycle very well adapted to the Polynesian environment; after numerous tests, the chemoprophylaxis with diethylcarbamazine (3 mg/kg/half-year) of all the exposed population has been decided, in association with methods of vector-control (use of predatory crustaceans). However, the achievement of this strategy is impeded by economical contingencies and the endemic comes up again particularly in areas close to eradication. Entomological clues show a high transmission over the greater part of French Polynesia.

District filariasis surveys in Tahiti in the years after the Second World War yielded the highest microfilaria rates in the South Pacific area, ranging from 25% to 44%; the mean elephantiasis rate was 5% and microfilaria densities (MfD(50)) ranged from 18 to 31. A co-operative filariasis research programme was begun and a control programme was inaugurated in 1953, using diethylcarbamazine therapy supported by mosquito larvae control measures. By 1959 fifteen districts had received mass treatment. Re-examination after 12 months showed that the mean microfilaria rate had dropped from 31% to 3% and the MfD(50) from 23 to 4. Subsequently, only positives were re-treated and by 1964 the microfilaria rate had risen to 6.8%. The increase caused concern and the significance of this reservoir of infection was investigated.Administration of diethylcarbamazine in periodic mass treatments only in American Samoa began in 1963 and was accompanied by a drop in the microfilaria rate to less than 1%, leading to interruption of transmission in some areas.

Filariasis surveys made during 1962-63 in 5 villages in American Samoa among persons over 5 years of age gave an elephantiasis rate of 3.4%, a microfilarial rate of 26% and a median microfilarial rate (MfD(50)) of 29. These rates were somewhat higher than those found in surveys made in the same villages among villagers of the same ages some 20 years previously. A mass treatment programme with diethylcarbamazine was then decided on.Preliminary treatment with a single total regimen of 72 mg of the drug per kg of body weight, given in 12 doses of 6 mg/kg, was administered in several villages over a period of 6 months. Among villagers of all ages at the end of 3 years, the microfilarial rate was 7.3% and the MfD(50) value was 2. These results appeared to be inadequate for a successful control programme and a periodic mass treatment project of 2 or more regimens of 72 mg/kg to be administered every 2 years was instituted on the Island of Tutuila, to be continued until considered no longer necessary.Surveys made 2 years after the second mass treatment in the villages of Amouli, Amanave, Onenoa, Tula, Alao, Utumea and Alofau, in which 1407 persons were examined, showed that 3 villages were negative for microfilariae, that the average microfilarial rate in all 7 villages was 0.4% and that the MfD(50) was 1. These villages were also negative in intensive mosquito surveys for infective-stage larvae of Wuchereria bancrofti. It is suggested that interruption of transmission has been observed in the 3 villages negative for both microfilariae and infective-stage larvae and that, if favourable surveys continue, eradication programmes should be established.