Impact of two rounds of mass treatment with diethylcarbamazine plus albendazole on Wuchereria bancrofti infection and the sensitivity of immunochromatographic test in Malindi, Kenya

Abstract

Annual single-dose mass treatment of endemic populations with a combination of either diethylcarbamazine (DEC) or ivermectin plus albendazole is recommended as the mainstay of lymphatic filariasis elimination programmes. We evaluated the impact of two rounds of annual mass drug administration (MDA) of DEC and albendazole on bancroftian filariasis in a pilot elimination programme in an endemic area of Kenya. Overall prevalence of microfilaraemia decreased by 65.4%, whereas community microfilarial load decreased by 84% after the two MDAs. The prevalence of parasite antigenaemia determined by immunochromatographic test (ICT) declined significantly by 43.5% after the two MDAs. We also studied the effect of mass treatment on the sensitivity of the ICT. Although the sensitivity of the test before treatment was high (89.9%; κ = 0.909) sensitivity was lower after two MDAs (59.3%; κ = 0.644). The finding raises concern about the reliability of the ICT in long-term monitoring of infection and for establishing programmatic endpoints. The results of the present study indicate a relatively high effectiveness of MDA using a DEC/albendazole combination against Wuchereria bancrofti infection and, therefore, it may be a useful strategy to eliminate lymphatic filariasis in onchocerciasis-free areas. Keywords Lymphatic filariasis Wuchereria bancrofti Mass drug administration Diethylcarbamazine Albendazole Kenya 1 Introduction The development of improved diagnostic tools and treatment strategies for human lymphatic filariasis in the 1990s led to optimism that the disease could be eliminated as a public health problem. In 2000, the WHO launched the Global Programme to Eliminate Lymphatic Filariasis (GPELF). The GPELF has two principal goals: to interrupt transmission of infection by reducing the levels of microfilariae (mf) in endemic communities through annual mass treatment, and to alleviate and prevent both the suffering and the disability caused by the disease ( Ottesen, 2000 ). Significant progress has been made by the GPELF in implementing elimination programmes at global, regional, national and sub-national levels ( Molyneux and Zagaria, 2002 ). Major success has been achieved by increasing treatment coverage from 3 million people in 2000 to 100 million in 2004 using the WHO-recommended combination drug strategy ( WHO, 2005 ). Based on models that estimate the reproductive lifespan of Wuchereria bancrofti to be approximately 5 years, it has been predicted that four to six rounds of annual mass drug administration (MDA) with treatment coverage of >80% might reduce microfilaraemia to levels that could interrupt transmission ( Norman et al., 2000; Plaisier et al., 1998 ). Efficient regular monitoring of W. bancrofti infection is especially important as the prevalence and levels of the infection decline due to the effect of widespread mass treatment with antifilarial drugs under GPELF. In addition, long-term epidemiological monitoring of filariasis elimination programmes is necessary to establish programmatic endpoints, as well as to conduct post-MDA surveillance ( Lammie et al., 2004 ). The GPELF recommends the use of microfilaraemia and circulating filarial antigen (CFA) detection by the immunochromatographic test (ICT) to monitor the impact of MDA on filarial infection ( WHO, 2000 ). Annual single-dose mass treatment of endemic populations with a combination of either diethylcarbamazine (DEC) or ivermectin plus albendazole is recommended as the mainstay of lymphatic filariasis elimination programmes ( Molyneux et al., 2000; Ottesen et al., 1997 ). In many areas of sub-Saharan Africa, where lymphatic filariasis and onchocerciasis are co-endemic, DEC cannot be used because it has previously been shown to cause severe side effects in individuals with Onchocerca volvulus mf ( Greene et al., 1985 ). Based on successful filariasis control efforts in China, and small-scale studies in other countries, DEC-fortified salt has been proposed as an additional option for the elimination of lymphatic filariasis ( Houston, 2000 ). There are reports on the effectiveness of DEC plus albendazole in filariasis elimination programmes linked to GPELF from several regions, including the south Pacific, Indonesia, south India and Egypt ( Fraser et al., 2005; Helmy et al., 2006; Oqueka et al., 2005; Rajendran et al., 2004 ) but none is available from sub-Saharan Africa. Kenya is unique in sub-Saharan Africa because DEC in combination with albendazole is the mass treatment regimen being used for the elimination of lymphatic filariasis, as onchocerciasis is not endemic. Successful interruption of transmission of O. volvulus by Simulium flies in Kenya through vector control with dichloro-diphenyl-trichloroethane (DDT) applications was first demonstrated in 1949 ( Roberts et al., 1967 ). The present study was designed to assess the impact of two rounds of annual mass treatment using co-administration of DEC and albendazole on bancroftian filariasis in a highly endemic area in the northern coast of Kenya. 2 Materials and methods 2.1 Study area In 2001, the W. bancrofti endemic area along River Sabaki in Malindi District, Kenya was selected for a pilot filariasis elimination project using single-dose annual mass treatment with DEC (6 mg/kg) plus albendazole (400 mg) under the GPELF. The present study was carried out in four sentinel communities, namely, Jilore, Marikano, Magongoloni and Mkondoni, selected for detailed long-term epidemiological monitoring of the impact of annual mass treatment ( Njenga et al., 2007 ). The total number of people living in the four sentinel communities in 2002 was 2611. The communities are typically rural and situated between 40 and 60 km west of Malindi town on the shores of the Indian Ocean and had never received mass treatment with antifilarial drugs before. 2.2 Study population The purpose of the present study was explained to the communities in the Kiswahili and Giriama languages...