Onchocerciasis, or river blindness, is a neglected tropical disease (NTD) that can cause visual impairment and debilitating and disfiguring skin disease. It is the world’s second leading cause of blindness due to infection and the world’s fourth leading cause of preventable blindness. It is a parasitic disease, caused by a filarial worm, and is transmitted by repeated bites from infected blackflies. It is called river blindness because the infected blackflies breed in rapidly flowing streams; villages situated along these streams are generally the most affected. There are an estimated 25 million individuals who are infected with onchocerciasis and another 123 million people who are at risk for the disease. There are an estimated 300,000 cases
…show more content…
Water is a necessary component of the blackflies environment because their larvae have an obligatory aquatic stage. The larvae attach to submerged rocks or vegetation where they develop into the adult form of the fly in approximately 8-10 days. The Sumulium fly lives for 4 weeks and can travel several hundred kilometers during its life course (Service et al., 2001). Flight distances of up to 79km over a period of 24 hours have been recorded by the female S. damnosum fly (Thompson, 1976). This allows onchocerciasis to be spread among many different villages. The Simulium adult female bites humans during the day, from dawn to dusk. If the bitten person is infected with onchocerciasis, O. volvulus microfilariae are ingested with the blood and then mature into the infected larvae state in one to three weeks. The infective larvae are then passed on to other people and mature into adult worms when the fly takes another blood meal (CDC, 2013). Thus, the Simulium blackfly acts an intermediate host for the parasite’s life …show more content…
Adult worms can live up to fifteen years in the human body. Male and female worms reside in groups coiled up in nodules in the subcutaneous tissue of the skin. The formation of the nodule emerges as a response of the host to foreign proteins. This causes an accumulation of excess leukocytes, fibroblasts, histiocytes and tissue cells around the blood cells which induces the formation of a granuloma. This granuloma, or mass of granulation tissue, is made up of macrophages which mature into epithelioid cells and fuse to create multinucleate foreign body giant cells, or nodules. The infiltrate that surrounds the nodules consists of macrophages, eosinophilic, mast cells, T and B lymphocytes, natural killer cells, and neutrophilic granulocytes (Brattig, 2004). Thus, the nodules, where the adult worms reside, act as a form of protection or barrier from the host’s immune
Water is a necessary component of the blackflies environment because their larvae have an obligatory aquatic stage. The larvae attach to submerged rocks or vegetation where they develop into the adult form of the fly in approximately 8-10 days. The Sumulium fly lives for 4 weeks and can travel several hundred kilometers during its life course (Service et al., 2001). Flight distances of up to 79km over a period of 24 hours have been recorded by the female S. damnosum fly (Thompson, 1976). This allows onchocerciasis to be spread among many different villages. The Simulium adult female bites humans during the day, from dawn to dusk. If the bitten person is infected with onchocerciasis, O. volvulus microfilariae are ingested with the blood and then mature into the infected larvae state in one to three weeks. The infective larvae are then passed on to other people and mature into adult worms when the fly takes another blood meal (CDC, 2013). Thus, the Simulium blackfly acts an intermediate host for the parasite’s life …show more content…
Adult worms can live up to fifteen years in the human body. Male and female worms reside in groups coiled up in nodules in the subcutaneous tissue of the skin. The formation of the nodule emerges as a response of the host to foreign proteins. This causes an accumulation of excess leukocytes, fibroblasts, histiocytes and tissue cells around the blood cells which induces the formation of a granuloma. This granuloma, or mass of granulation tissue, is made up of macrophages which mature into epithelioid cells and fuse to create multinucleate foreign body giant cells, or nodules. The infiltrate that surrounds the nodules consists of macrophages, eosinophilic, mast cells, T and B lymphocytes, natural killer cells, and neutrophilic granulocytes (Brattig, 2004). Thus, the nodules, where the adult worms reside, act as a form of protection or barrier from the host’s immune