Abstract
The Republic of Angola is a priority country for onchocerciasis and lymphatic filariasis (LF) elimination, however, the co-distribution of the filarial parasite Loa loa (loiasis) is a significant impediment, due to the risk of severe adverse events (SAEs) associated with ivermectin used in mass drug administration (MDA) campaigns. Angola has a high risk loiasis zone identified in Bengo Province where alternative interventions may need to be implemented; however, the presence and geographical overlap of the three filarial infections/diseases are not well defined. Therefore, this study conducted a rapid integrated filarial mapping survey based on readily identifiable clinical conditions of each disease in this risk zone to help determine prevalence and co-distribution patterns in a timely manner with limited resources. In total, 2007 individuals from 29 communities in five provincial municipalities were surveyed. Community prevalence estimates were determined by the rapid assessment procedure for loiasis (RAPLOA) and rapid epidemiological mapping of onchocerciasis (REMO) together with two questions on LF clinical manifestations (presence of lymphoedema, hydrocoele). Overall low levels of endemicity, with different overlapping distributions were found. Loiasis was found in 18 communities with a prevalence of 2.0% (31/1571), which contrasted to previous results defining the area as a high risk zone. Onchocerciasis prevalence was 5.3% (49/922) in eight communities, and LF prevalence was 0.4% for lymphoedema (8/2007) and 2.6% for hydrocoeles (20/761 males) in seven and 12 communities respectively. The clinical mapping survey method helped to highlight that all three filarial infections are present in this zone of Bengo Province. However, the significant difference in loiasis prevalence found between the past and this current survey suggests that further studies including serological and parasitological confirmation are required. This will help determine levels of infection and risk, understand the associations between clinical, serological and parasitological prevalence patterns, and better determine the most appropriate treatment strategies to reach onchocerciasis and LF elimination targets in the loiasis co-endemic areas. Our results also suggest that the utility of the earlier RAPLOA derived maps, based on surveys undertaken over a decade ago, are likely to be invalid given the extent of population movement and environmental change, particularly deforestation, and that fine scale micro-mapping is required to more precisely delineate the interventions required defined by these complex co-endemicities.
Highlights
The Republic of Angola is a priority country for onchocerciasis and lymphatic filariasis (LF) elimination in sub-Saharan Africa (World Health Organization, 2015a, 2015b; World Health Organization, 2016a, 2016b)
The problem of severe adverse events (SAEs) associated with ivermectin was initially reported during mass drug administration (MDA) in onchocerciasis control programmes in Cameroon and later in the Democratic Republic of Congo (DRC), as a result of which, the African Programme for Onchocerciasis Control (APOC) (Cupp et al, 2011; Dadzie, 1997) developed the rapid assessment survey method for loiasis (RAPLOA) based on eye worm history (Addiss et al, 2003; Takougang et al, 2002; Wanji et al, 2005, 2012)
The study was conducted in rural and semi-rural villages across six municipalities in the north-western province of Bengo, Angola where the loiasis endemicity was considered to be high as determined by a previous RAPLOA study, the onchocerciasis endemicity was moderate to low as determined by rapid epidemiological mapping of onchocerciasis (REMO), and the LF endemicity low as determined by recent published modelled maps, including historical records, which were imported into ArcGIS 10 (ESRI, Redlands CA) and digitized to created new maps with comparative prevalence/endemicity levels for the purpose of this study (Fig. 1A–D) (Cano et al, 2014; Zouré et al, 2011, 2014)
Summary
The Republic of Angola is a priority country for onchocerciasis and lymphatic filariasis (LF) elimination in sub-Saharan Africa (World Health Organization, 2015a, 2015b; World Health Organization, 2016a, 2016b) These two human filarial infections are key neglected tropical diseases (NTDs) listed by the World Health Organization (WHO), and considered to be major public health problems, causing widespread disability and consequent poverty (World Health Organization, 2012a; World Health Organization, 2013a, 2013b, 2016c). The problem of SAEs associated with ivermectin was initially reported during MDA in onchocerciasis control programmes in Cameroon and later in the Democratic Republic of Congo (DRC), as a result of which, the African Programme for Onchocerciasis Control (APOC) (Cupp et al, 2011; Dadzie, 1997) developed the rapid assessment survey method for loiasis (RAPLOA) based on eye worm history (Addiss et al, 2003; Takougang et al, 2002; Wanji et al, 2005, 2012). Advice to national onchocerciasis elimination programmes about how the risk of SAEs should be mitigated, and if they occur, be managed is based on the Guidelines established by the Mectizan Donation Programme Expert Committee (the Mectizan Expert Committee, MEC) (Addiss et al, 2003; Alleman et al, 2006; Colatrella, 2008; Ogoussan and Hopkins, 2011), with technical expertise from the new Expanded Special Project for Elimination of Neglected Tropical Diseases (ESPEN) (Hopkins, 2016; World Health Organization, 2015a, 2015b)
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