title: Vector-parasite transmission complexes for onchocerciasis in West Africa.
abstract: BACKGROUND
  In West Africa, there are two strains of the filarial parasite Onchocerca volvulus, which differ in their ability to induce ocular disease. Transmission studies have suggested that six sibling species of the parasite vector, the black fly Simulium damnosum sensu lato, allow development of the two strains of O volvulus with varying efficiency. We aimed to test the hypothesis of parasite-vector complexes, whereby the two parasite strains, known as forest and savanna, are preferentially transmitted by distinct groups of the species of S damnosum S l.
  
  
  METHODS
  During 1993 and 1994, wild black flies were collected from 11 river basins within the area covered by the Onchocerciasis Control Programme (OCP). The flies were dissected and filarial larvae, ovaries, and malpighian tubules removed. Genomic DNA was extracted from larvae, and PCR amplification was used to classify O volvulus parasites as forest or savanna strains. PCR-amplified DNA from ovaries and malpighian tubules was used to distinguish sibling species of S damnosum s l. S yahense and S squamosum were distinguished by body colour.
  
  
  RESULTS
  214 of 105105 flies dissected were infected with filarial larvae; 84 of these were infected with mature O volvulus parasites. Of the 35 savanna-dwelling infected flies. 17 carried forest-strain parasites and 18 savanna-strain parasites. Of the 45 infected flies identified as the forest dwelling sibling species. 20 carried savanna-strain parasites and 25 forest-strain parasites. No significant differences were found in the numbers of mature larvae of each strain carried by the forest-dwelling species of fly or in the number of forest and savanna larvae in savanna-dwelling vector species.
  
  
  CONCLUSIONS
  Vector-parasite transmission complexes do not currently play a part in the biology of O volvulus transmission in the area of the OCP in West Africa. This finding has important strategic implications for the future of efforts to control onchocerciasis in West Africa.
authors.affiliation: DNA Diagnostics Laboratory, Onchocerciasis Control Programme in West Africa, Bouake, Ivory Coast.
authors.forename: L
authors.initials: L
authors.lastname: Toé
authors.forename: J
authors.initials: J
authors.lastname: Tang
authors.forename: C
authors.initials: C
authors.lastname: Back
authors.forename: C R
authors.initials: CR
authors.lastname: Katholi
authors.forename: T R
authors.initials: TR
authors.lastname: Unnasch
mesh_terms: D000354:Africa, Western; D000818:Animals; D004247:DNA; D005260:Female; D006801:Humans; D007303:Insect Vectors / Q000469:parasitology*; D007814:Larva / Q000235:genetics; D009854:Onchocerca / Q000145:classification / Q000469:parasitology*; D009855:Onchocerciasis / Q000635:transmission*; D016133:Polymerase Chain Reaction; D012843:Simuliidae / Q000145:classification / Q000235:genetics / Q000469:parasitology*; D013045:Species Specificity
chemical_list: D004247:DNA