Abstract
The Republic of Angola is a priority country for onchocerciasis and lymphatic filariasis (LF) elimination, however, the co-distribution of loiasis, caused by the filarial parasite Loa loa, is a significant impediment. This is due to the increasing risk of severe adverse effects (SAEs) associated with ivermectin treatment(s) when used in mass drug administration (MDA) campaigns in Loa loa endemic areas. In Bengo province, Angola a putative high-risk, but under-surveyed, endemic zone for loiasis exists where alternative intervention(s) may need to be implemented. Within this province, the presence and geographical overlap(s) of the three filarial infections are not well defined.
Furthermore, knowledge gaps in the vector biology of Loa loa exist. To this end, I undertook a twophased epidemiological investigation of the three filarial diseases and I provided an upto-date assessment of the biology of Chrysops, the insect vector of loiasis. In the latter I placed special focus upon opportunities to develop better vector control.
In Phase 1, 2007 individuals from 29 communities from Bengo province were surveyed. Community prevalence estimates were determined by Rapid Assessment Procedure for Loiasis (RAPLOA) and Rapid Epidemiological Mapping of Onchocerciasis (REMO) together with two questions on LF clinical manifestations (presence of lymphoedema and
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). This contrasted to previous results which predicted this area to be a high-risk zone. Onchocerciasis prevalence was 5.3% (49/922) in eight communities, and lymphatic filariasis prevalence was 0.4% for lymphoedema (8/2007) and 2.6% for hydroceles (20/761 males) in seven and twelve communities, respectively. The clinical mapping survey method helped to highlight that all three filarial infections are present in this zone of Bengo province and their fine scale spatial patterns.
In Phase 2, a novel combination of clinical, serological and DNA
diagnostics was applied, where 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 Loa loa, 6.2% (n = 100/1616) 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. Loa loa prevalence in longterm residents (>10 years) and older individuals (>60 years) were significantly higher, 5
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 (Ov16 ELISA), with only three individuals reporting to have ever taken ivermectin. For W. bancrofti, no infection was found using the antigen-based immunochromatographic test (ICT) and real-time PCR analysis; however, 27 individuals presented with 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. Taken as a whole, my results evidence that the utility of the earlier RAPLOA
derived maps, based on surveys undertaken over a decade ago, are in need of revision and updating given the extent of population movement and environmental change, particularly deforestation. In future, further fine scale micro-mapping is required to more precisely delineate most appropriate interventions required for these complex co-endemic
diseases.
| Date of Award | 2020 |
|---|---|
| Original language | English |
| Supervisor | Russell Stothard (Supervisor) & Louise Kelly-Hope (Supervisor) |