The 0150 Repeat Family As A Tool To Study Relationships Among O Volvulus Populations

Since the 20th century, it had been known that onchocerciasis exhibited two distinct clinical presentations in West Africa. In the rainforest bioclime, a nonblinding form of the disease existed where onchocercal blindness was rare, even in hyperendemic areas. In the savanna bioclime, a blinding form of the disease was endemic, where onchocercal blindness was common. Epidemiological, entomological, pathological, biochemical, and immunological studies all supported the hypothesis that this difference was linked to the fact that two distinct strains of the parasite were endemic to the rainforest and savanna bioclimes of West Africa. Before the development of the 0-150 PCR, a DNA probe derived from the 0-150 repeat sequence family (pFS-1) was identified that hybridized only to parasite isolates collected from the forested regions.[5] Following the development of the 0-150 PCR, this probe was used to classify PCR products from villages from West Africa that exhibited blinding or nonblinding epidemiological disease patterns. The results demonstrated an almost perfect correspondence of the probe classification and disease pattern.[20] This suggested that the differences in disease pattern were due to genetic differences in the parasite populations and that the 0-150 PCR, when used in conjunction with strain-specific probes, was capable of distinguishing the two strains.

The discovery that the 0-150 repeat family was variable enough to differentiate the forest and savanna strains of O. volvulus in West Africa suggested that it might also be used as a tool to study the relationships among other populations of O. volvulus. For example, strain-specific probes developed to classify West African parasites have been used in studies of O. volvulus from Uganda,[21] which suggested that Ugandan parasites might form a population that was distinct from those found in West Africa. Similarly, extensive analyses were carried out on the 0-150 families from West African parasites and those from Sudan and the Americas.[22,23] The results demonstrated that, as expected, parasites from the savanna and forest bioclimes of West Africa were statistically different from one another. Parasites from Southern Sudan were statistically indistinguishable from those in the West African savanna in keeping with the fact that onchocerciasis is endemic throughout the wide savanna zone spanning the entire continent of Africa from east to west. In contrast, parasites from the Abu Hamad focus of onchocerciasis in Northern Sudan were distinct from both West African strains.[23] The Abu Hamad focus is isolated from all other foci of O. volvulus by the desert, and the vector there is a distinct species of Simulium damnosum s.l. Parasites from Guatemala and Brazil were found to be distinguishable from the forest strain of West African O. volvulus but were indistinguishable from savanna strain parasites.[22] This finding supported the hypothesis that O. volvulus was introduced into the Americas as a result of the trade in African slaves, as the majority of the slaves imported into both Guatemala and Brazil originated from the savanna areas of West Africa.

Getting Started With Dumbbells

Getting Started With Dumbbells

The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.

Get My Free Ebook


Post a comment