Descriptions of members of theSimulium damnosumcomplex (Diptera: Simuliidae) from southern Africa, Ethiopia and Tanzania

Cytotaxonomic characterization and estimation of migration patterns of onchocerciasis vectors (Simulium damnosum sensu lato) in northwestern Ethiopia based on RADSeq data

BACKGROUND

While much progress has been made in the control and elimination of onchocerciasis across Africa, the extent to which vector migration might confound progress towards elimination or result in re-establishment of endemism in areas where transmission has been eliminated remains unclear. In Northern Ethiopia, Metema and Metekel-two foci located near the Sudan border-exhibit continuing transmission. While progress towards elimination has been faster in Metema, there remains a problematic hotspot of transmission. Whether migration from Metekel contributes to this is currently unknown.

METHODOLOGY/PRINCIPLE FINDINGS

To assess the role of vector migration from Metekel into Metema, we present a population genomics study of 151 adult female vectors using 47,638 RADseq markers and mtDNA CoI sequencing. From additional cytotaxonomy data we identified a new cytoform in Metema, closely related to S. damnosum s.str, here called the Gondar form. RADseq data strongly indicate the existence of two distinctly differentiated clusters within S. damnosum s.l.: one genotypic cluster found only in Metema, and the second found predominantly in Metekel. Because blackflies from both clusters were found in sympatry (in all four collection sites in Metema), but hybrid genotypes were not detected, there may be reproductive barriers preventing interbreeding. The dominant genotype in Metema was not found in Metekel while the dominant genotype in Metekel was found in Metema, indicating that (at the time of sampling) migration is primarily unidirectional, with flies moving from Metekel to Metema. There was strong differentiation between clusters but little genetic differentiation within clusters, suggesting migration and gene flow of flies within the same genetic cluster are sufficient to prevent genetic divergence between sites.

CONCLUSIONS/SIGNIFICANCE

Our results confirm that Metekel and Metema represent different transmission foci, but also indicate a northward movement of vectors between foci that may have epidemiological importance, although its significance requires further study.

Esperanza Window Traps for the collection of anthropophilic blackflies (Diptera: Simuliidae) in Uganda and Tanzania

There is an increasing need to evaluate the impact of chemotherapeutic and vector-based interventions as onchocerciasis affected countries work towards eliminating the disease. The Esperanza Window Trap (EWT) provides a possible alternative to human landing collections (HLCs) for the collection of anthropophilic blackflies, yet it is not known whether current designs will prove effective for onchocerciasis vectors throughout sub-Saharan Africa. EWTs were deployed for 41 days in northern Uganda and south eastern Tanzania where different Simulium damnosum sibling species are responsible for disease transmission. The relative efficacy of EWTs and HLCs was compared, and responses of host-seeking blackflies to odour baits, colours, and yeast-produced CO2 were investigated. Blue EWTs baited with CO2 and worn socks collected 42.3% (2,393) of the total S. damnosum s.l. catch in northern Uganda. Numbers were comparable with those collected by HLCs (32.1%, 1,817), and higher than those collected on traps baited with CO2 and BG-Lure (25.6%, 1,446), a synthetic human attractant. Traps performed less well for the collection of S. damnosum s.l. in Tanzania where HLCs (72.5%, 2,432) consistently outperformed both blue (16.8%, 563) and black (10.7%, 360) traps baited with CO2 and worn socks. HLCs (72.3%, 361) also outperformed sock-baited (6.4%, 32) and BG-Lure-baited (21.2%, 106) traps for the collection of anthropophilic Simulium bovis in northern Uganda. Contrasting blackfly distributions were observed on traps in Uganda and Tanzania, indicating differences in behaviour in each area. The success of EWT collections of S. damnosum s.l. in northern Uganda was not replicated in Tanzania, or for the collection of anthropophilic S. bovis. Further research to improve the understanding of behavioural responses of vector sibling species to traps and their attractants should be encouraged.

Cytotaxonomic description ofSimulium kaffaense, a new member of theS. damnosumcomplex (Diptera: Simuliidae) from south–western Ethiopia

Although Ethiopia is one of the countries worst affected by human onchocerciasis, the exact taxonomic identity of the blackflies acting as the main vectors in the endemic areas has never been determined. A cytotaxonomic analysis of Simulium damnosum s.l. collected from three endemic sites in south-western Ethiopia has now revealed the existence of the 'Kisiwani' form (a non-anthropophilic cytoform that is common in East Africa) and a newly recognized species, Simulium kaffaense. Simulium kaffaense sp. nov. is differentiated from other members of the S. damnosum complex by six fixed inversions and dozens of 'new' floating inversions. The rearing of egg batches from some of the biting adult females, to larvae or adults, indicated that the human-biting blackflies were all S. kaffaense. As S. kaffaense is not only highly anthropophilic but also, apparently, the only anthropophilic member of the S. damnosum complex present, it is likely to be the main (if not the only) vector of Onchocerca volvulus in the study area. The presence of inversion 1S-1 and a complex inversion possibly involving 1L-3 indicates that S. kaffaense either belongs or is close to the 'Nile' phylogenetic group of S. damnosum s. l. The karyotype frequencies of the inversions in the collections from the three study sites indicate that at least two forms of S. kaffaense, here designated 'Bebeka' and 'Jimma', were caught. The taxonomy and medical importance of S. kaffaense are discussed.

Taxonomy and inventory of the cytospecies and cytotypes of the Simulium damnosum complex (Diptera: Simuliidae) in relation to onchocerciasis

We provide an inventory of all named cytoforms of the Simulium damnosum complex (including those which are now considered invalid), along with all inversions that have been recorded (including synonyms and homonyms). There are 55 valid and distinct cytoforms known from the S. damnosum complex making it the largest sibling species complex of any vectors, and probably of any insect or other animal. All cytoforms are listed along with their fixed and diagnostic inversions and country distribution. There are 183 inversions known from the complex as a whole, of which 49% are fixed and/or diagnostic between cytoforms, and the fixed/diagnostic inversions seem to occur disproportionately on chromosome arm 2L.

Revision of the Ketaketa subcomplex of blackflies of the Simulium damnosum complex

A revision of the taxonomy of the Ketaketa subcomplex of the Simulium damnosum Theobald complex (Diptera: Simuliidae) is presented including new material from Tanzania, Malawi and South Africa. The cytotaxonomy, morphology and molecular identity of known and new taxa are described. The Ketaketa subcomplex is cytotaxonomically defined by the paracentric inversion 1L-7. We recognize three sibling species, namely Simulium latipollex (Enderlein), Simulium plumbeum Krueger, sp.n. and Simulium kipengere Krueger, sp.n., the latter comprising three cytoforms: 'Typical', 'Linthipe' and 'Mombo'. The cytoforms 'Mwamphanzi', 'Ketaketa' and 'Hammerkopi' are synonymized with S. plumbeum. Identification keys are provided on the basis of chromosomal and morphological characters. In view of their potential role as vectors of human onchocerciasis (river blindness) we also discuss the possible medical importance of the different cytoforms and their geographical distribution.

Guide to blackflies of the Simulium damnosum complex in eastern and southern Africa

At least 26 members of the Simulium damnosum Theobald complex (Diptera: Simuliidae) are known from eastern Africa, most of which are assumed to be non-anthropophilic and some are restricted to small areas of endemicity. Their discovery was based on polytene chromosome inversion polymorphisms and since then they have been cited as cytological entities, but, in many cases, with inadequate descriptions (e.g. without illustrations of the chromosomes). The present distribution, taxonomy and vector identity have been re-evaluated during the last decade in conjunction with ongoing onchocerciasis control programmes. Here, a summary of the relevant data is presented, integrating results of cytotaxonomic, morphotaxonomic and molecular investigations into a guide that provides a comprehensive system of identification for the cytoforms 'Kagera', 'Kasyabone', 'Kibwezi', 'Kisiwani', 'Kisiwani E', 'Kulfo', 'Linthipe', 'Mombo', 'Mutonga', 'Njombe', 'Nkusi', 'Nkusi SA', 'Nkusi SW', 'Nyika', 'Pienaars', 'Sanje', 'Sebwe', 'Turiani', Simulium damnosum sensu stricto, Simulium kaffaense Hadis et al., Simulium kilibanum Gouteux, Simulium kipengere Krueger, Simulium latipollex (Enderlein), Simulium pandanophilum Krüger, Nurmi & Garms, Simulium plumbeum Krueger, Simulium thyolense Vajime et al. and for five newly recognized molecular forms of 'Nkusi' and S. kilibanum. All taxa except S. pandanophilum are assigned to one of five subcomplexes (damnosum, Ketaketa, Kibwezi, Sanje, squamosum) within the S. damnosum complex. The guide encompasses anthropophilic and non-anthropophilic segregates for the whole of eastern and southern Africa, and is not restricted to larval chromosome criteria; in many cases it also allows the typing of adult flies.

Molecular phylogenetics of blackflies of the Simulium damnosum complex and cytophylogenetic implications

The molecular phylogenetics of the Simulium damnosum complex, including vectors of the human parasite Onchocerca volvulus, from various parts of Africa was studied and compared with results of cytogenetic analyses. The sequence data of mitochondrial 16s and nuclear ITS2 rDNA revealed that the complex comprises two main clades, roughly covering the more easterly and westerly African taxa, respectively. However, striking inconsistencies in the tree topologies turned up between the DNA fragments regarding the position of certain subcomplexes and species. The cytophylogenetic relationships are better reflected in the ITS2 tree where Simulium pandanophilum and Simulium mengense constitute a basal, Central African clade of the entire complex and are therefore suggested to be the chromosomal roots too. Further divisions and the corresponding biogeographic interpretations are discussed. Several species and cytoforms are placed within the system for the first time. The phylogenetic relationships within the complex do hardly correlate with host preferences or other behavioral and ecological characteristics.