Isolation by distance and a chromosomal cline in the Cayapa cytospecies of Simulium exiguum, the vector of human onchocerciasis in Ecuador.

The population genetic structure of the Cayapa cytospecies of Simulium exiguum, the vector of onchocerciasis, was analysed using allozyme frequency and chromosomal inversion polymorphism data from 6 and 15 populations respectively, collected in Ecuador. Eight allozyme loci were scored. No unique allozyme markers were found enabling us to identify biting adults of the vector from the non-vector Bucay cytotype.

The potential for dispersal of onchocerciasis in Ecuador in relation to the distribution of the vector Simulium exiguum (Diptera:Simuliidae).

The future dispersal of onchocerciasis in Ecuador is dependent on the distribution of cytotypes of the vector species complex Simulium exiguum. Over the last 14 years, collections of larvae have been made from over 25 rivers, between 80-1600 m altitude, from various sites on both sides of the Andes. Analysis of larval polytene chromosomes was used to determine the distributions of each cytotype.

Cytological and isoenzyme analysis of the Bucay and Quevedo cytotypes of the Onchocerciasis vector Simulium exiguum (Diptera: Simuliidae) in Ecuador.

Four cytotypes of Simulium exiguum occur in Ecuador, where this morphospecies is the primary vector of onchocerciasis. In this paper, we give the first full description of the banding pattern of the larval polytene chromosomes of the Quevedo cytotype and assess its degree of genetic separation from the Bucay cytotype. Both cytotypes differ from the chromosomal standard sequence (of the Cayapa cytotype) by the fixed inversions IIL-5 and IIL-6.

Seasonal variation in onchocerciasis transmission in the Santiago focus of Ecuador.

Man-biting rates and natural infection rates with filariae were determined for anthropophilic black flies in a preliminary survey during the wet and dry seasons at three localities, either hypoendemic or hyperendemic for onchocerciasis, in the Santiago onchocerciasis focus of Ecuador. Simulium exiguum was an efficient vector associated with hyperendemicity whereas S. quadrivittatum was thought only to sporadically transmit the parasite.