Transmission indices and microfilariae prevalence in human population prior to mass drug administration with ivermectin and albendazole in the Gomoa District of Ghana
Date
2015-10
Journal Title
Journal ISSN
Volume Title
Publisher
Parasites & Vectors
Abstract
Lymphatic filariasis (LF) is a disease that can lead to elephantiasis and hydrocoele as the main clinical manifestations. About 120 million people in 83 countries in the tropical and subtropical regions of the world are infected, with an estimated 1.34 billion people at risk [1] (WHO 2010–2020). The disease is caused by three species of filarial worms namely Wuchereria bancrofti, Brugia timori and B. malayi. Among them, W. bancrofti causes over 90 % of all LF cases [2] (WHO internet May 2015). Lymphatic filariasis has been identified as the second leading causes of permanent and long-term disability in the world [3] (WHO 1995). The disease is rarely fatal, but clinical manifestations carry grave personal and sociocultural consequences for those affected and their immediate family members. The disease can result in sexual dysfunction, divorce and victims are often not suitable for marriage [4, 5, 6, 7, 8, 9, 10] (Gyapong et al., 1996; Gyapong et al., 1996; Gyapong et al., 2000; Dreyer et al., 1997; Ramaiah et al., 1997; 3–9 Coreil et al., 1998; Ahorlu et al., 1999). The disease also negatively impacts on the work output of affected individuals and victims are often subjects of public ridicule [11] (Dunyo et al., 1996).
The disease has been targeted for elimination by the World Health Organization (WHO) through yearly mass drug administration (MDA) of ivermectin and albendazole or diethylcarbamazine to inhabitants of endemic communities [12] (Turner). The drugs are usually given in single doses continuously for 4-6 years, until adult worms have reached the end of their reproductive lifespan. In situations where coverage is low, MDA must be extended in order to interrupt transmission [13] (WHO 2011, Geneva). The elimination strategy is based on the postulation that should microfilarial reservoir in the human host be reduced below a certain threshold, transmission of Wuchereria bancrofti by anopheline vectors could be interrupted, a phenomenon known as facilitation [14, 15, 16] (Weber 1991; Southgate & Bryan 1992; Bockarie et al., 1998). For example, findings from Papua New Guinea (PNG) showed that transmission by Anopheles punctulatus was virtually stopped after a year of treatment, although the frequency of microfilariae (mf) carriers in the human population ranged from 10.5–52.7 % [16] (Bockarie et al., 1998). However, it may not be practicable to generalise this PNG observation worldwide. In the West African sub region, several species of Anopheles, which are vectors of bancroftian LF occur in sympatry, contrary to the situation in PNG where the disease was transmitted by only one vector species [17] deSouza et alThe threshold of mf frequency needed for elimination of anopheline-transmitted W. bancrofti LF may differ from one vector species to another and from one community to another. Additionally, the co-existence of W. bancrofti and Plasmodium falciparum in most LF endemic communities has led to an interesting relationships being developed between these two parasites. One parasite tends to dominate in prevalence/importance over the other and vice versa at certain points in time during the year, despite sharing similar Anopheles vectors and environmental factors that support their survival and multiplication in West Africa [18] (Kelly-Hope et al. 2006). Variations in both human infection burden and the associated environmental and entomological factors influencing the transmission of both diseases may account for the prevalence patterns exhibited, which could in turn affect local LF control efforts.
Many well-meaning and carefully planned control programmes have failed to achieve their desired targets because these programmes have often overlooked the role of community members in those endemic areas [19] (Wynd et al., 2007). It has been observed that views and behaviour of people towards an illness either enhance or interfere with the effectiveness of control measures [20] (Bentum). In addition, participation in control efforts may not be optimum if the communities perceive lymphatic filariasis as a less important health problem [10] (Ahorlu et al.). Since the mainstay for the control programme is not morbidity control but transmission blockage through chemotherapy, the success of such a strategy depends largely on the level of coverage of the drug administration to the target population. Hence understanding community perceptions about the disease is vital to encouraging maximum participation [19] (Wynd et al., 2007).
In view of this, there is the need to monitor and evaluate the trends in transmission of W. bancrofti by Anopheles species and the human microfilaria densities in the sub-region before, during and after MDA with ivermectin and albendazole to ensure successful LF elimination. The Ministry of Health of the Republic of Ghana initiated its elimination programme in line with WHO recommendation in the year 2000. To complement their efforts towards the elimination of LF, the Noguchi Memorial Institute for Medical Research (Ghana) established sentinel sites in one of the endemic districts in southern Ghana to monitor the national control programme through parasitological and entomological surveys. The resulting data from this monitoring activity were fed into the programme as a means of enhancing its implementation at community level. The study herein reported was conducted to assess the views and perceptions of persons, as well as document vector transmission indices and mf prevalence in the human population in eight endemic communities in the Gomoa district of Ghana.
Description
Keywords
Perceptions, Baseline indices, Human microfilariae, Anopheles species, Transmission, Ghana