Taking the strain out of onchocerciasis? A reanalysis of blindness and transmission data does not support the existence of a savannah blinding strain of onchocerciasis in West Africa

Cheke, Robert; Little, Kirsty; Young, Stephen; Walker, Martin; Basáñez, María‐Gloria

doi:10.1016/bs.apar.2021.01.002

Cited by 8 publications

(5 citation statements)

References 115 publications

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“…Various species of the S. damnosum complex present different transmission efficiencies [ 5 ] hence, increased diversity may lead to complex epidemiology of onchocerciasis. For example, S. squamosum and S. mengense (the major onchocerciasis vectors in the Southwest and Northwest regions) have been shown to present bilateral blindness similar to what has previously been established for savanna vectors [ 33 ]. Generally, there were no seasonal changes in species composition in the different regions.…”

Section: Discussionmentioning

confidence: 75%

A cross-sectional study of Simulium damnosum sensu lato breeding sites and species distribution in Sudan savanna, mixed savanna–forest and rainforest regions in Cameroon

Ayisi

Sedou²,

Dieunang

et al. 2022

Parasites Vectors

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Background The presence of breeding sites and distribution of species of Simulium damnosum sensu lato are critical in understanding the epidemiology of onchocerciasis and evaluating the impact of elimination interventions. Reports on breeding sites and species distribution of members of S. damnosum s.l. in Cameroon are scarce and the few ones available date back to more than three decades. The aim of this study is to provide information on S. damnosum breeding sites across the rainy (RS) and dry (DS) seasons and the species composition in three different regions in Cameroon: Southwest (SW), Northwest (NW) and North (N). Methods A cross-sectional two-season study was carried out in three regions with different ecological characteristics (SW—rainforest; NW—mixed forest–Guinea savanna; N—Sudan savanna). Pre-control onchocerciasis endemicity, relief maps and historical entomological information were used to identify potential rivers for purposive sampling. Sampled larvae were fixed in Carnoy’s solution and sorted, and S. damnosum s.l. larvae were stored until identification by cytotaxonomy. Geographical coordinates of potential breeding sites were recorded to produce maps using ArcGIS, while Chi-square tests in SPSS were used to test for any differences between black fly seasonal breeding rates. Results A total of 237 potential breeding sites were sampled (RS = 81; DS = 156) and 72 were found positive for S. damnosum s.l. The SW had the most positive sites [67 (RS = 24; DS = 43)], with a significant difference in the rate of breeding between the seasons (P < 0.05). Among 68 sites visited in both seasons, 16 (23.5%) were positive in one of the two seasons with more sites positive in DS(11) than RS(05), 14 (20.6%) and 38 (55.9%) respectively positive and negative in both seasons. Simulium damnosum sensu stricto and S. sirbanum were the main species in the N, while S. squamosum and S. mengense were the predominant species in the NW and SW. Simulium soubrense and S. yahense were uniquely recorded in the SW. Conclusions A comprehensive mapping of breeding sites requires rainy and dry seasons sampling. This study demonstrates that a breeding site survey of S. damnosum s.l. is achievable in forest as well as savanna zones. Not all potential breeding sites are actual breeding sites. Observation of S. soubrense in the SW indicates changes in species composition over time and could affect onchocerciasis epidemiology in this area. Graphical abstract

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Section: Discussionmentioning

confidence: 75%

A cross-sectional study of Simulium damnosum sensu lato breeding sites and species distribution in Sudan savanna, mixed savanna–forest and rainforest regions in Cameroon

Ayisi

Sedou²,

Dieunang

et al. 2022

Parasites Vectors

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“…It has been suggested that blindness is more prevalent in savannah than in forest onchocerciasis areas. However, a recent meta-analysis did not support the existence of a savannah-blinding strain of onchocerciasis in West Africa [30].…”

Section: Discussionmentioning

confidence: 94%

High Prevalence of Glaucoma among Patients in an Onchocerciasis Endemic Area (Mahenge, Tanzania)

et al. 2022

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Onchocerciasis is known to cause skin lesions and blindness, but there is also epidemiological evidence that onchocerciasis is associated with epilepsy, including nodding syndrome. We carried out ocular exams in persons with epilepsy in Mahenge, an onchocerciasis endemic area with a high prevalence of epilepsy in Tanzania. We recruited 278 consecutive persons with epilepsy attending the epilepsy clinic at Mahenge hospital and satellite clinics in rural villages. They underwent a general physical and a detailed ocular examination and were tested for onchocerciasis Ov16 IgG4 antibodies. Glaucoma was defined by a raised intraocular pressure above 21 mmHg with evidence of typical glaucomatous disc changes in one or both eyes. Among the 278 participants, median age 27 (IQR 21–38) years, 55.4% were female; 151/210 (71.9%) (95% CI: 65.3–77.9) were Ov16 positive. The most frequent ophthalmic lesions were glaucoma (33.1%), vitreous opacities (6.5%) and cataracts (2.9%). In multivariate analysis, glaucoma (adjusted IRR = 1.46; 95% CI: 1.24–1.70) and age (adjusted IRR = 1.01; 95% CI: 1.01–1.02) were significantly associated with onchocerciasis. In conclusion, a high prevalence of glaucoma was observed among Ov16 positive persons with epilepsy. Persons with epilepsy with O. volvulus infection should undergo screening for glaucoma to prevent one of the causes of preventable blindness.

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“…Differences between the manifestation of onchocerciasis in forest and savannah regions, in particular between blinding rates, gave rise to a two-strain hypothesis (Duke et al 1966). Analyses of entomological data (Cheke and Garms, 2013) and a reanalysis of pre-control blindness data (Cheke et al, 2020) have led to this hypothesis being questioned. Although some molecular studies of different O. volvulus populations revealed differences between savannah and forest strains, for instance by being distinguishable using the O-150 repeat region sequence (Erttmann et al, 1987;Zimmermann et al, 1992), other studies did not (Morales-Hojas et al, 2007).…”

Section: Phylogeny and Biology Of Onchocercamentioning

confidence: 99%

Onchocerciasis (river blindness) – more than a century of research and control

2021

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This historical review on River Blindness, onchocerciasis, is written in honour of (i) the 120-year anniversary of the Bernhard Nocht Institute for Tropical Medicine (BNITM), founded in 1900 in Hamburg in the sequel of a tremendous cholera outbreak that hit Hamburg in 1892, (ii) the 75-year anniversaries of Acta Tropica and (iii) the Swiss Tropical and Public Health Institute (Swiss TPH), both founded in 1944 in Basel by the renowned scientist of tropical medicine Rudolf Geigy . Geigy was the first director of the former Swiss Tropical Institute (STI) and simultaneously the first editor of Acta Tropica.River Blindness caused by the tissue filaria Onchocerca volvulus was one focus of research in the BNITM over almost 60 years documented in about 300 publications. Consequently, in this historical review article we have cited major articles based on research conducted at the BNITM.In addition to this historical review article on onchocerciasis two historical articles on 75 year of both, Acta Tropica and Swiss TPH, are jointly published in in one issue of Acta Tropica.

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Taking the strain out of onchocerciasis? A reanalysis of blindness and transmission data does not support the existence of a savannah blinding strain of onchocerciasis in West Africa

Cited by 8 publications

References 115 publications

A cross-sectional study of Simulium damnosum sensu lato breeding sites and species distribution in Sudan savanna, mixed savanna–forest and rainforest regions in Cameroon

A cross-sectional study of Simulium damnosum sensu lato breeding sites and species distribution in Sudan savanna, mixed savanna–forest and rainforest regions in Cameroon

High Prevalence of Glaucoma among Patients in an Onchocerciasis Endemic Area (Mahenge, Tanzania)

Onchocerciasis (river blindness) – more than a century of research and control

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