Onchocerca volvulus: limited heterogeneity in the nuclear and mitochondrial genomes.

West African populations of Onchocerca volvulus endemic to the rain forest and savanna bioclimes of West Africa differ in their ability to induce ocular disease in infected individuals. In recent years, both clinical- and animal-model-based studies have implicated particular parasite antigens in the development of ocular onchocerciasis. To test the hypothesis that the difference in pathogenic potential of blinding and nonblinding parasites might be reflected in qualitative differences in antigens that have been implicated in the development of ocular onchocerciasis, we compared the sequences of two parasite antigens implicated in the development of ocular disease in blinding- and nonblinding-strain parasites. The results demonstrated a high level of homogeneity between the parasite strains in these genes. The study was extended to include additional nuclear genes encoding antigens that are commonly recognized by individuals infected with O. volvulus and to the mitochondrial genome of the parasite. The results demonstrate a high degree of homogeneity in both the nuclear and the mitochondrial genomes among O. volvulus isolates collected from several different sites in Africa and in the Americas. This high degree of genetic homogeneity may reflect the passage of the parasite through a recent genetic bottleneck.