Abstract
BackgroundGhana is renowned for its sibling species diversity of the Simulium damnosum complex, vectors of Onchocerca volvulus. Detailed entomological knowledge becomes a priority as onchocerciasis control policy has shifted from morbidity reduction to elimination of infection. To date, understanding of transmission dynamics of O. volvulus has been mainly based on S. damnosum sensu stricto (s.s.) data. We aim to elucidate bionomic features of vector species of importance for onchocerciasis elimination efforts.MethodsWe collected S. damnosum sensu lato from seven villages in four Ghanaian regions between 2009 and 2011, using standard vector collection, and human- and cattle-baited tents. Taxa were identified using morphological and molecular techniques. Monthly biting rates (MBR), parous rates and monthly parous biting rates (MPBR) are reported by locality, season, trapping method and hour of collection for each species.ResultsS. damnosum s.s./S. sirbanum were collected at Asubende and Agborlekame, both savannah villages. A range of species was caught in the Volta region (forest-savannah mosaic) and Gyankobaa (forest), with S. squamosum or S. sanctipauli being the predominant species, respectively. In Bosomase (southern forest region) only S. sanctipauli was collected in the 2009 wet season, but in the 2010 dry season S. yahense was also caught. MBRs ranged from 714 bites/person/month at Agborlekame (100% S. damnosum s.s./S. sirbanum) to 8,586 bites/person/month at Pillar 83/Djodji (98.5% S. squamosum). MBRs were higher in the wet season. In contrast, parous rates were higher in the dry season (41.8% vs. 18.4%), resulting in higher MPBRs in the dry season. Daily host-seeking activity of S. damnosum s.s./S. sirbanum was bimodal, whilst S. squamosum and S. sanctipauli had unimodal afternoon peaks.ConclusionsThe bionomic differences between sibling species of the S. damnosum complex need to be taken into account when designing entomological monitoring protocols for interventions and parameterising mathematical models for onchocerciasis control and elimination.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-014-0511-9) contains supplementary material, which is available to authorized users.
Highlights
Ghana is renowned for its sibling species diversity of the Simulium damnosum complex, vectors of Onchocerca volvulus
Study area Study sites were selected according to vector species, bioclimatic zone, vector control, ivermectin distribution history, and variability in village size and domestic animal populations, during a preliminary survey conducted between 27th April and 14th May 2009, when blackfly larvae were collected from breeding sites for cytotaxonomic identification [1]
Data analysis This paper focuses on the numbers of each simuliid species, expressed as the monthly biting rates (MBRs), caught in each locality and season, the percentages of parous flies, and the monthly parous biting rates (MBPR) summarising the density of host-seeking flies that constitute the epidemiologically important section of the biting population
Summary
Ghana is renowned for its sibling species diversity of the Simulium damnosum complex, vectors of Onchocerca volvulus. Ghana has a great diversity of sibling species of the Simulium damnosum complex [1], vectors of Onchocerca volvulus, the causative agent of human onchocerciasis or river blindness [2]. Adult populations of the important West African sibling species found in Ghana—S. damnosum sensu stricto (s.s.) Vajime and Dunbar, S. sirbanum Vajime and Dunbar, S. sanctipauli Vajime and Dunbar, S. yahense Vajime and Dunbar, S. soubrense Beffa form [9], and S. squamosum Enderlein (of which both C and E forms occur) —can be distinguished to morphospecies [5,10], and individuals of S. yahense can be identified [11]. Almost all adult blackflies from Ghana can be fully distinguished to species using a combination of morphological [5,12,13,14,15] and molecular techniques, with S. squamosum lacking a 10-base pair indel from the non-transcribed H3-H4 histone intergenic spacer region [16]
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