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Stapley JN, Hamley JID, Walker M, Dixon MA, Colebunders R, Basáñez MG. Modelling onchocerciasis-associated epilepsy and the impact of ivermectin treatment on its prevalence and incidence. Nat Commun 2024; 15:6275. [PMID: 39054334 PMCID: PMC11272922 DOI: 10.1038/s41467-024-50582-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Accepted: 07/15/2024] [Indexed: 07/27/2024] Open
Abstract
Retrospective cohort studies in Cameroon found an association between Onchocerca volvulus microfilarial load in childhood (measured in 1991-1993) and risk of developing epilepsy later in life (measured in 2017). We parameterised and integrated this relationship (across children aged 3-15 years) into the previously published, stochastic transmission model, EPIONCHO-IBM, for Simulium damnosum sensu lato-transmitted onchocerciasis. We simulated 19 years (1998-2017) of annual ivermectin mass drug administration (MDA) reflecting coverage in the study area, and modelled epilepsy prevalence and incidence. Scenario-based simulations of 25 years of (annual and biannual) MDA in hyper- and holoendemic settings, with 65% and 80% therapeutic coverage, were also conducted. EPIONCHO-IBM predicted 7.6% epilepsy prevalence (compared to 8.2% in the Cameroon study) and incidence of 317 cases/100,000 person-years (compared to 350). In hyperendemic areas, 25 years of biannual MDA (80% coverage) eliminated onchocerciasis-associated epilepsy (OAE) and protected untreated under-fives from its development. Strengthening onchocerciasis programmes, implementing alternative strategies, and evaluating treatment for under-fives and school-age children are crucial to prevent OAE in highly-endemic settings.
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Affiliation(s)
- Jacob N Stapley
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK.
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK.
| | - Jonathan I D Hamley
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK
- Department of Visceral Surgery and Medicine, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland
- Multidisciplinary Center for Infectious Diseases, University of Bern, Bern, Switzerland
| | - Martin Walker
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK
- Department of Pathobiology and Population Sciences, Royal Veterinary College, Hatfield, UK
| | - Matthew A Dixon
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK
| | | | - Maria-Gloria Basáñez
- MRC Centre for Global Infectious Disease Analysis, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK.
- London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, London, UK.
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Siewe Fodjo JN, Ekome SRE, Njamnshi JNT, Njamnshi WY, Njamnshi KG, Ngarka L, Njamnshi AK. Community Perceptions of Blackfly Nuisance and Acceptability of the "Slash and Clear" Vector Control Approach in the Ntui Health District of Cameroon: A Qualitative Study. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2024; 21:658. [PMID: 38928904 PMCID: PMC11204025 DOI: 10.3390/ijerph21060658] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2024] [Revised: 05/15/2024] [Accepted: 05/19/2024] [Indexed: 06/28/2024]
Abstract
Besides being vectors of the onchocerciasis parasite, blackflies are a source of nuisance in onchocerciasis-endemic communities. We investigated the experience of residents in the Ntui Health District (Cameroon) regarding blackfly nuisance and assessed their perceptions of a novel "Slash and Clear" (S&C) intervention for blackfly control. Focus group discussions were conducted before and after S&C implementation (respectively, in February 2022 and December 2023). Blackflies were known to emerge from the river areas and cause disease. To prevent blackfly bites, the population often covered their body with protective clothing and applied various substances (kerosene, oil, or lemon) to their skin. Post-intervention data showed reduced blackfly nuisance, and the willingness to sustain blackfly control in the long-term was unanimous among community leaders and members, including the village volunteers who implemented the S&C intervention. In conclusion, blackfly nuisance is evident in the Ntui onchocerciasis focus of Cameroon and led to a panoply of coping practices, some of which could be detrimental to their health. Implementing S&C for blackfly control is well accepted and could sustainably alleviate the nuisance caused by blackflies while simultaneously breaking the onchocerciasis transmission cycle.
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Affiliation(s)
- Joseph Nelson Siewe Fodjo
- Brain Research Africa Initiative (BRAIN), Yaoundé P.O. Box 25625, Cameroon; (S.R.E.E.); (J.N.T.N.); (W.Y.N.); (K.G.N.); (L.N.)
- Global Health Institute, University of Antwerp, Doornstraat 331, 2610 Antwerp, Belgium
| | - Serge Raoul Ekukole Ekome
- Brain Research Africa Initiative (BRAIN), Yaoundé P.O. Box 25625, Cameroon; (S.R.E.E.); (J.N.T.N.); (W.Y.N.); (K.G.N.); (L.N.)
| | - Julius Ndi Taryunyu Njamnshi
- Brain Research Africa Initiative (BRAIN), Yaoundé P.O. Box 25625, Cameroon; (S.R.E.E.); (J.N.T.N.); (W.Y.N.); (K.G.N.); (L.N.)
| | - Wepnyu Yembe Njamnshi
- Brain Research Africa Initiative (BRAIN), Yaoundé P.O. Box 25625, Cameroon; (S.R.E.E.); (J.N.T.N.); (W.Y.N.); (K.G.N.); (L.N.)
- Division of Operational Research in Health, Ministry of Public Health, N°8 Rue 3038 quartier du Lac (Yaoundé III), Yaoundé P.O. Box 3595, Cameroon
| | - Kongnyu G. Njamnshi
- Brain Research Africa Initiative (BRAIN), Yaoundé P.O. Box 25625, Cameroon; (S.R.E.E.); (J.N.T.N.); (W.Y.N.); (K.G.N.); (L.N.)
| | - Leonard Ngarka
- Brain Research Africa Initiative (BRAIN), Yaoundé P.O. Box 25625, Cameroon; (S.R.E.E.); (J.N.T.N.); (W.Y.N.); (K.G.N.); (L.N.)
- Neuroscience Lab, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé 1, Yaoundé P.O. Box 1364, Cameroon
- Neurology & Clinical Neuroscience Department, Yaoundé Central Hospital, Yaoundé P.O. Box 87, Cameroon
| | - Alfred K. Njamnshi
- Brain Research Africa Initiative (BRAIN), Yaoundé P.O. Box 25625, Cameroon; (S.R.E.E.); (J.N.T.N.); (W.Y.N.); (K.G.N.); (L.N.)
- Neuroscience Lab, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé 1, Yaoundé P.O. Box 1364, Cameroon
- Neurology & Clinical Neuroscience Department, Yaoundé Central Hospital, Yaoundé P.O. Box 87, Cameroon
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Doherty M, Grant JR, Pilotte N, Bennuru S, Fischer K, Fischer PU, Lustigman S, Nutman TB, Pfarr K, Hoerauf A, Unnasch TR, Hassan HK, Wanji S, Lammie PJ, Ottesen E, Mackenzie C, Williams SA. Optimized strategy for real-time qPCR detection of Onchocerca volvulus DNA in pooled Simulium sp. blackfly vectors. PLoS Negl Trop Dis 2023; 17:e0011815. [PMID: 38096317 PMCID: PMC10754622 DOI: 10.1371/journal.pntd.0011815] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2023] [Revised: 12/28/2023] [Accepted: 11/22/2023] [Indexed: 12/30/2023] Open
Abstract
BACKGROUND Onchocerca volvulus is a filarial parasite that is a major cause of dermatitis and blindness in endemic regions primarily in sub-Saharan Africa. Widespread efforts to control the disease caused by O. volvulus infection (onchocerciasis) began in 1974 and in recent years, following successful elimination of transmission in much of the Americas, the focus of efforts in Africa has moved from control to the more challenging goal of elimination of transmission in all endemic countries. Mass drug administration (MDA) with ivermectin has reached more than 150 million people and elimination of transmission has been confirmed in four South American countries, with at least two African countries having now stopped MDA as they approach verification of elimination. It is essential that accurate data for active transmission are used to assist in making the critical decision to stop MDA, since missing low levels of transmission and infection can lead to continued spread or recrudescence of the disease. METHODOLOGY/PRINCIPAL FINDINGS Current World Health Organization guidelines for MDA stopping decisions and post-treatment surveillance include screening pools of the Simulium blackfly vector for the presence of O. volvulus larvae using a PCR-ELISA-based molecular technique. In this study, we address the potential of an updated, practical, standardized molecular diagnostic tool with increased sensitivity and species-specificity by comparing several candidate qPCR assays. When paired with heat-stable reagents, a qPCR assay with a mitochondrial DNA target (OvND5) was found to be more sensitive and species-specific than an O150 qPCR, which targets a non-protein coding repetitive DNA sequence. The OvND5 assay detected 19/20 pools of 100 blackfly heads spiked with a single L3, compared to 16/20 for the O150 qPCR assay. CONCLUSIONS/SIGNIFICANCE Given the improved sensitivity, species-specificity and resistance to PCR inhibitors, we identified OvND5 as the optimal target for field sample detection. All reagents for this assay can be shipped at room temperature with no loss of activity. The qPCR protocol we propose is also simpler, faster, and more cost-effective than the current end-point molecular assays.
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Affiliation(s)
- Mary Doherty
- Department of Biological Sciences, Smith College, Northampton, Massachusetts, United States of America
| | - Jessica R. Grant
- Department of Biological Sciences, Smith College, Northampton, Massachusetts, United States of America
| | - Nils Pilotte
- Department of Biological Sciences, Quinnipiac University, Hamden, Connecticut, United States of America
| | - Sasisekhar Bennuru
- Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland, United States of America
| | - Kerstin Fischer
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Peter U. Fischer
- Department of Medicine, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Sara Lustigman
- Laboratory of Molecular Parasitology, Lindsley F. Kimball Research Institute, New York Blood Center, New York, New York, United States of America
| | - Thomas B. Nutman
- Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland, United States of America
| | - Kenneth Pfarr
- Institute of Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany
- German Center for Infection Research (DZIF), Partner-Site Bonn-Cologne, Bonn, Germany
| | - Achim Hoerauf
- Institute of Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany
- German Center for Infection Research (DZIF), Partner-Site Bonn-Cologne, Bonn, Germany
| | - Thomas R. Unnasch
- Center for Global Health Infectious Disease Research, University of South Florida, Tampa, Florida, United States of America
| | - Hassan K. Hassan
- Center for Global Health Infectious Disease Research, University of South Florida, Tampa, Florida, United States of America
| | - Samuel Wanji
- Parasite and Vectors Research Unit, Department of Microbiology and Parasitology, University of Buea, Buea, Cameroon
- Research Foundation in Tropical Diseases and the Environment, Buea, Cameroon
| | - Patrick J. Lammie
- NTD-SC, Task Force for Global Health, Atlanta, Georgia, United States of America
| | - Eric Ottesen
- NTD-SC, Task Force for Global Health, Atlanta, Georgia, United States of America
| | - Charles Mackenzie
- NTD-SC, Task Force for Global Health, Atlanta, Georgia, United States of America
- RLMF, The END Fund, New York, New York, United States of America
| | - Steven A. Williams
- Department of Biological Sciences, Smith College, Northampton, Massachusetts, United States of America
- Molecular and Cellular Biology Program, University of Massachusetts, Amherst, Massachusetts, United States of America
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Ngarka L, Siewe Fodjo JN, Ambomatei C, Njamnshi WY, Taryunyu Njamnshi JN, Nfor LN, Mengnjo MK, Njamnshi AK. Epidemiology of epilepsy and relationship with onchocerciasis prevalence in villages of the Ntui Health District of Cameroon. Epilepsy Behav 2023; 142:109184. [PMID: 36972641 PMCID: PMC7614422 DOI: 10.1016/j.yebeh.2023.109184] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Revised: 03/13/2023] [Accepted: 03/14/2023] [Indexed: 03/29/2023]
Abstract
BACKGROUND A strong association between epilepsy and onchocerciasis endemicity has been reported. We sought to document the epidemiology of epilepsy in onchocerciasis-endemic villages of the Ntui Health District in Cameroon and investigate how this relates to the prevalence of onchocerciasis. METHODS In March 2022, door-to-door epilepsy surveys were conducted in four villages (Essougli, Nachtigal, Ndjame, and Ndowe). Ivermectin intake during the 2021 session of community-directed treatment with ivermectin (CDTI) was investigated in all participating village residents. Persons with epilepsy (PWE) were identified through a two-step approach: administration of a 5-item epilepsy screening questionnaire followed by clinical confirmation by a neurologist. Epilepsy findings were analyzed together with onchocerciasis epidemiological data previously obtained in the study villages. RESULTS We surveyed 1663 persons in the four study villages. The 2021 CDTI coverage for all study sites was 50.9%. Overall, 67 PWE were identified (prevalence of 4.0% (IQR: 3.2-5.1) with one new-onset case during the past 12 months (annual incidence of 60.1 per 100,000 persons). The median age of PWE was 32 years (IQR: 25-40), with 41 (61.2%) being females. The majority (78.3%) of PWE met the previously published criteria for onchocerciasis-associated epilepsy (OAE). Persons with a history of nodding seizures were found in all villages and represented 19.4% of the 67 PWE. Epilepsy prevalence was positively correlated with onchocerciasis prevalence (Spearman Rho = 0.949, p = 0.051). Meanwhile, an inverse relationship was observed between distance from the Sanaga river (blackfly breeding site) and the prevalence of both epilepsy and onchocerciasis. CONCLUSION The high epilepsy prevalence in Ntui appears to be driven by onchocerciasis. It is likely that decades of CDTI have likely contributed to a gradual decrease in epilepsy incidence, as only one new case occurred in the past year. Therefore, more effective elimination measures are urgently needed in such endemic areas to curb the OAE burden.
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Affiliation(s)
- Leonard Ngarka
- Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon; Neurology Department, Central Hospital Yaoundé, Yaoundé, Cameroon; Neuroscience Lab, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé I, Yaoundé, Cameroon.
| | - Joseph Nelson Siewe Fodjo
- Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon; Division of Operational Research in Health, Ministry of Public Health, Yaoundé, Cameroon.
| | | | - Wepnyu Yembe Njamnshi
- Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon; Neuroscience Lab, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé I, Yaoundé, Cameroon; Division of Operational Research in Health, Ministry of Public Health, Yaoundé, Cameroon.
| | | | - Leonard N Nfor
- Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon; Neurology Department, Central Hospital Yaoundé, Yaoundé, Cameroon.
| | - Michel K Mengnjo
- Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon; Neurology Department, Central Hospital Yaoundé, Yaoundé, Cameroon.
| | - Alfred K Njamnshi
- Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon; Neurology Department, Central Hospital Yaoundé, Yaoundé, Cameroon; Neuroscience Lab, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé I, Yaoundé, Cameroon.
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Siewe Fodjo JN, Ngarka L, Njamnshi WY, Enyong PA, Zoung-Kanyi Bissek AC, Njamnshi AK. Onchocerciasis in the Ntui Health District of Cameroon: epidemiological, entomological and parasitological findings in relation to elimination prospects. Parasit Vectors 2022; 15:444. [PMID: 36443885 PMCID: PMC9702945 DOI: 10.1186/s13071-022-05585-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 09/20/2022] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND Despite decades of community-directed treatment with ivermectin (CDTI), onchocerciasis transmission persists in Cameroon and has been associated with increased risk for epilepsy in endemic communities. We investigated the onchocerciasis situation in the Ntui Health District (a known onchocerciasis focus in Cameroon where the Sanaga River constitutes the main source of black fly vectors) using parasitological, entomological and serological parameters. METHODS In July 2021, community-based surveys were conducted in four villages (Essougli, Nachtigal, Ndjame and Ndowe). Onchocerciasis was diagnosed via microscopic examination of skin snips. Using rapid diagnostic tests, we screened children aged 3-6 years for Ov16 antibodies as a proxy for recent onchocerciasis transmission. Monthly black fly biting rates were obtained from the two riverside villages (Nachtigal and Essougli) for 12 consecutive months (July 2021 to June 2022) using the human landing catch technique. Some black flies were dissected each month to check for infection. RESULTS Overall, 460 participants were recruited; mean age was 32.1 (range: 3-85) years with 248 (53.9%) being males. Among skin snipped participants (n = 425), onchocerciasis prevalence was 14.6%. Participants with epilepsy (n = 25) were more often skin snip positive (45.8% vs 12.7%; P < 0.001) and had higher microfilarial loads (9.2 ± 22.0 vs 0.7 ± 3.5 microfilariae/skin snip; P < 0.001) compared to their peers without epilepsy. Eight (6.5%) of the 123 tested children were Ov16 seropositive. The breeding sites we investigated along the Sanaga River during the current study harbored fewer vectors (annual biting rates reaching 530,322 vs 606,370 in the Mbam River) and exhibited lower black fly infection rates (annual transmission potentials reaching 1479 vs 4488 in the Mbam River) when compared to recent entomological reports in Cameroon. CONCLUSION Despite substantial biting rates, black fly infection rates (by microscopy) in the Ntui Health District were rather low resulting in overall low transmission potentials in study villages. Thanks to CDTI, O. volvulus infection in both humans and insects is on the decrease. However, there is evidence that O. volvulus is still endemic in these communities. Reducing the vector population will further accelerate onchocerciasis elimination prospects.
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Affiliation(s)
- Joseph Nelson Siewe Fodjo
- Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon ,grid.460723.40000 0004 0647 4688Neurology Department, Central Hospital Yaoundé, Yaoundé, Cameroon
| | - Leonard Ngarka
- Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon ,grid.460723.40000 0004 0647 4688Neurology Department, Central Hospital Yaoundé, Yaoundé, Cameroon ,grid.412661.60000 0001 2173 8504Neuroscience Lab, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé I, Yaoundé, Cameroon
| | - Wepnyu Yembe Njamnshi
- Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon ,grid.412661.60000 0001 2173 8504Neuroscience Lab, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé I, Yaoundé, Cameroon ,grid.415857.a0000 0001 0668 6654Ministry of Public Health, Division of Health Operations Research, Yaoundé, Cameroon
| | - Peter Ayuk Enyong
- grid.29273.3d0000 0001 2288 3199Research Foundation in Tropical Diseases and Environment (REFOTDE), Buea, Cameroon
| | - Anne-Cécile Zoung-Kanyi Bissek
- Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon ,grid.412661.60000 0001 2173 8504Neuroscience Lab, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé I, Yaoundé, Cameroon ,grid.415857.a0000 0001 0668 6654Ministry of Public Health, Division of Health Operations Research, Yaoundé, Cameroon
| | - Alfred Kongnyu Njamnshi
- Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon ,grid.460723.40000 0004 0647 4688Neurology Department, Central Hospital Yaoundé, Yaoundé, Cameroon ,grid.412661.60000 0001 2173 8504Neuroscience Lab, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé I, Yaoundé, Cameroon
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Hendy A, Krit M, Pfarr K, Laemmer C, De Witte J, Nwane P, Kamgno J, Nana-Djeunga HC, Boussinesq M, Dujardin JC, Post R, Colebunders R, O'Neill S, Enyong P, Njamnshi AK. Onchocerca volvulus transmission in the Mbam valley of Cameroon following 16 years of annual community-directed treatment with ivermectin, and the description of a new cytotype of Simulium squamosum. Parasit Vectors 2021; 14:563. [PMID: 34727965 PMCID: PMC8561987 DOI: 10.1186/s13071-021-05072-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2021] [Accepted: 10/16/2021] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The onchocerciasis focus surrounding the lower Mbam and Sanaga rivers, where Onchocerca volvulus is transmitted by Simulium damnosum s.l. (Diptera: Simuliidae), was historically the largest in the southern regions of Cameroon. Annual community-directed treatment with ivermectin (CDTI) has been taking place since 2000, but recent studies have shown that new infections are occurring in children. We aimed to investigate blackfly biting and O. volvulus transmission rates along the lower Mbam river 16 years after the formal onset of annual CDTI. METHODS Black flies were collected for three consecutive days each month between July 2016 and June 2017 at two riverside villages and two inland sites situated 4.9 km and 7.9 km from the riverside. Specimens collected at each site were dissected on one of the three collection days each month to estimate parity rates and O. volvulus infection rates, while the remaining samples were preserved for pool screening. RESULTS In total, 93,573 S. damnosum s.l. black flies were recorded biting humans and 9281 were dissected. Annual biting rates of up to 606,370 were estimated at the riverside, decreasing to 20,540 at 7.9 km, while, based on dissections, annual transmission potentials of up to 4488 were estimated at the riverside, decreasing to 102 and 0 at 4.9 km and 7.9 km, respectively. However, pool screening showed evidence of infection in black flies at the furthest distance from the river. Results of both methods demonstrated the percentage of infective flies to be relatively low (0.10-0.36%), but above the WHO threshold for interruption of transmission. In addition, a small number of larvae collected during the dry season revealed the presence of Simulium squamosum E. This is the first time S. squamosum E has been found east of Lake Volta in Ghana, but our material was chromosomally distinctive, and we call it S. squamosum E2. CONCLUSIONS Relatively low O. volvulus infection rates appear to be offset by extremely high densities of biting black flies which are sustaining transmission along the banks of the lower Mbam river.
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Affiliation(s)
- Adam Hendy
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium. .,Department of Pathology, University of Texas Medical Branch, Galveston, TX, USA.
| | - Meryam Krit
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Kenneth Pfarr
- Institute for Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany.,German Center for Infection Research, Partner Site Bonn-Cologne, Cologne, Germany
| | - Christine Laemmer
- Institute for Medical Microbiology, Immunology and Parasitology, University Hospital Bonn, Bonn, Germany.,German Center for Infection Research, Partner Site Bonn-Cologne, Cologne, Germany
| | - Jacobus De Witte
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Philippe Nwane
- Centre for Research on Filariasis and Other Tropical Diseases (CRFilMT), Yaoundé, Cameroon
| | - Joseph Kamgno
- Centre for Research on Filariasis and Other Tropical Diseases (CRFilMT), Yaoundé, Cameroon.,Department of Public Health, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé I, Yaoundé, Cameroon
| | - Hugues C Nana-Djeunga
- Centre for Research on Filariasis and Other Tropical Diseases (CRFilMT), Yaoundé, Cameroon
| | - Michel Boussinesq
- Institut de Recherche pour le Développement (IRD), Montpellier, France
| | - Jean-Claude Dujardin
- Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Rory Post
- Department of Disease Control, London School of Hygiene and Tropical Medicine, London, UK.,School of Natural Sciences and Psychology, Liverpool John Moores University, Liverpool, UK
| | | | - Sarah O'Neill
- Department of Public Health, Institute of Tropical Medicine, Antwerp, Belgium.,CR 5, Ecole de Santé Publique, Université Libre de Bruxelles, Brussels, Belgium
| | - Peter Enyong
- Research Foundation in Tropical Diseases and Environment, Buea, Cameroon
| | - Alfred K Njamnshi
- Neuroscience Lab, Faculty of Medicine and Biomedical Sciences, The University of Yaoundé I, Yaoundé, Cameroon.,Brain Research Africa Initiative (BRAIN), Yaoundé, Cameroon.,Brain Research Africa Initiative (BRAIN), Geneva, Switzerland.,Neurology Department, Central Hospital Yaoundé, Yaoundé, Cameroon
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7
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Raimon S, Lakwo TL, Sebit WJ, Siewe Fodjo JN, Alinda P, Carter JY, Post RJ, Colebunders R. "Slash and Clear", a Community-Based Vector Control Method to Reduce Onchocerciasis Transmission by Simulium sirbanum in Maridi, South Sudan: A Prospective Study. Pathogens 2021; 10:pathogens10101329. [PMID: 34684277 PMCID: PMC8538802 DOI: 10.3390/pathogens10101329] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2021] [Revised: 10/11/2021] [Accepted: 10/13/2021] [Indexed: 11/25/2022] Open
Abstract
Background: High ongoing Onchocerca volvulus transmission was recently documented in Maridi County, South Sudan. To complement community-directed treatment with ivermectin (CDTI) as the main onchocerciasis control strategy, we initiated a community-based vector control method “slash and clear” at the Maridi dam, a Simulium damnosum s.l. breeding site, to reduce O. volvulus transmission. Methods: Simulium damnosum s.l. biting rates were collected before and during the twenty months following the “slash and clear” intervention using the human landing catches. Black flies were dissected to measure parity rates before and twelve months after the intervention. Larvae and pupae of S. damnosum s.l. were collected from the dam for morphological and chromosomal characterization to identify the cytospecies involved. Results: Biting rates of S. damnosum s.l. close to the Maridi dam spillway decreased by >90% post-“slash and clear” for more than six months. Twelve months after the “slash and clear” intervention, the reduction in biting rates was still at <50% (p = 0.0007). Parity rates reduced from 13% pre-“slash and clear” (November 2019) to 5.6% post-“slash and clear” (November 2020). Larvae collected from the dam were identified as Simulium sirbanum. Conclusion: The “slash and clear” method was found to be an effective and cheap community-based method to reduce black fly biting rates caused by S. sirbanum. When repeated at least annually together with a high CDTI coverage, this intervention has the potential to considerably accelerate onchocerciasis elimination.
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Affiliation(s)
| | - Tom L. Lakwo
- Vector Control Division, Ministry of Health, Kampala P.O. Box 1661, Uganda; (T.L.L.); (P.A.)
| | - Wilson John Sebit
- Public Health Laboratory, Ministry of Health, May Rd, Juba P.O. Box 30125, South Sudan;
| | | | - Peter Alinda
- Vector Control Division, Ministry of Health, Kampala P.O. Box 1661, Uganda; (T.L.L.); (P.A.)
| | - Jane Y. Carter
- Amref Health Africa Headquarters, Nairobi P.O. Box 27691-00506, Kenya;
| | - Rory J. Post
- Disease Control Department, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK;
- School of Biological and Environmental Sciences, Liverpool John Moores University, Liverpool L3 5UG, UK
| | - Robert Colebunders
- Global Health Institute, University of Antwerp, 2610 Antwerp, Belgium;
- Correspondence: ; Tel.: +32-4-8692-0149
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