Abstract
The prevalence of Loa loa, Onchocerca volvulus and Wuchereria bancrofti infections in an under-surveyed area of Bengo Province, Angola, was determined by surveying 22 communities with a combination of clinical, serological and DNA diagnostics. Additional information was collected on participants' duration of residency, access to mass drug administration, knowledge of insect vectors and use of bednets. A total of 1616 individuals (38.1% male: 61.9% female), with an average age of 43 years, were examined. For L. loa, 6.2% (n = 100/16616) individuals were found to have eyeworm, based on the rapid assessment procedure for loiasis (RAPLOA) surveys, and 11.5% (n =178/1543) based on nested PCR analyses of venous blood. L. loa prevalences in long-term residents (>10 years) and older individuals (>60 years) were significantly higher, and older men with eyeworm were better informed about Chrysops vectors. For O. volvulus, 4.7% (n = 74/1567) individuals were found to be positive by enzyme-linked immunosorbent assay (Ov 16 ELISA), with only three individuals reporting to have ever taken ivermectin. For W. bancrofti, no infections were found using the antigen-based immunochromatographic test (ICT) and real-time PCR analysis; however, 27 individuals presented with lymphatic filariasis (LF) related clinical conditions (lymphoedema = 11, hydrocoele = 14, both = 2). Just under half (45.5%) of the participants owned a bednet, with the majority (71.1%) sleeping under it the night before. Our approach of using combination diagnostics reveals the age-prevalence of loiasis alongside low endemicity of onchocerciasis and LF. Future research foci should be on identifying opportunities for more cost-effective ways to eliminate onchocerciasis and to develop innovative surveillance modalities for clinical LF for individual disease management and disability prevention.
Highlights
Of the main filarial nematode diseases in sub-Saharan Africa, onchocerciasis caused by Onchocerca volvulus, and lymphatic filariasis (LF) caused by Wuchereria bancrofti account for the greatest public health burden (World Health Organization, 2012a)
Onchocerciasis and LF are both endemic in the Republic of Angola and the national neglected tropical disease (NTD) programme is working to scale-up preventive chemotherapy, by mass drug administration (MDA), to interrupt transmission with the longterm aim of disease elimination (World Health Organization, 2016)
This is of concern in low prevalence onchocerciasis areas, that are co-endemic with a high prevalence of loiasis areas, as ivermectin is not recommended and no safe, scalable alternative interventions are available (Bockarie et al, 2013)
Summary
Of the main filarial nematode diseases in sub-Saharan Africa, onchocerciasis caused by Onchocerca volvulus, and lymphatic filariasis (LF) caused by Wuchereria bancrofti account for the greatest public health burden (World Health Organization, 2012a). In high L. loa prevalence communities, large-scale MDA of ivermectin is not advised as life-threatening serious adverse events (SAEs) can occur in individuals with high levels of L. loa microfilaraemia (Gardon et al, 1997; Zouré et al, 2011) This is of concern in low prevalence onchocerciasis areas (i.e. hypo-endemic), that are co-endemic with a high prevalence of loiasis areas (i.e. hyper-endemic), as ivermectin is not recommended and no safe, scalable alternative interventions are available (Bockarie et al, 2013). In 2014, the main alternative method to serodiagnosis of loiasis was laboratorybased polymerase chain reaction (PCR), for onchocerciasis the enzyme-linked immunosorbent assay (Ov16 ELISA) and for LF the rapid diagnostic immunochromatographic test (ICT) and laboratory-based PCR (Weil and Ramzy, 2007; Kelly-Hope et al, 2018a). As a follow-up of the first filarial clinical mapping survey in Dande Municipality, Bengo Province (Brito et al, 2017), the objective of this current study was to examine the prevalence of filarial infections across the study areas using a combination of serological and molecular methods
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