Submitted to: Scanning
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 2001
Publication Date: N/A
Interpretive Summary: River blindness, also know as onchocerciasis, is a tropical disease that is prevalent in humans in many areas of Africa and South America. The disease is caused by a small microscopic worm called Onchocerca volvulus. This worm is spread by black flies, which transmit the parasite by biting humans, who become the hosts for the developing worms. Eventually, infection with the parasite causes blindness in humans. Scientists are attempting to develop a vaccine for this disease but must have additional information about how the worms develop and how they are transmitted. This study used a powerful microscope, called a scanning electron microscope, to view the development of the worm in the black fly and to see how the fly might transmit the worm. These results, which show the different stages of development and when they occur, will be used by research groups that are attempting to develop a vaccine to prevent the disease.
Development and morphology of Onchocerca volvulus larvae in the Simulium yahense were examined by Nomarski interference light microscopy and by scanning electron microscopy (SEM). The black flies (S. yahense) were fed on volunteers infected with O. volvulus microfilariae and reared in an insectary. The infected flies were sampled, dissected and recovered under the light microscope. Other samples were cryo-preserved, shipped to the U. S. and revived by thawing from the deep freezed cryoprotectant. The larval development was photographed by Nomarski interference light microscopy and by SEM. From the examined material, the developmental times and the changes in larval morphology from microfilaria to infective larvae were determined. Observations of the larval morphology and organogenesis were concentrated primarily on the cephalic and caudal regions of the developing larvae. The detrimental effect of O. volvulus larvae on their hosts was evident from the low survival of infected flies and from damage observed in the external and internal regions by SEM.