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Med Trop (Mars),
1997]
Before the 1980s, the only available method for control of onchocerciasis was elimination of blackfly vector populations. This strategy was used with considerable success in the Onchocerciasis Control Programme in West Africa (OCP). The discovery of ivermectin, the first effective drug suitable for mass treatment of onchocerciasis, has revived international interest not only in fundamental research but also in development of new strategies to control onchocerciasis in the countries outside the OCP area. This report gives an overview of current parasitological, clinical, epidemiological and diagnostic data about onchocerciasis. Although little is known about the early development of Onchocerca volvulus in the human host, significant insight has been gained into the population dynamics of the parasite. The pathogenesis of cutaneous and ocular manifestations in onchocerciasis is now better understood. Epidemiological studies are under way to evaluate the extent of systemic manifestations. Recently developed diagnostic methods are more sensitive than conventional parasitological techniques. A new method for rapid assessment of endemic level has provided a detailed picture of the distribution of onchocerciasis. Species- and strain-specific DNA probes have been developed for identification of parasites in West Africa. New methods for quantifying disability allow evaluation of the socio-economic impact of the cutaneous and ocular complications of onchocerciasis.
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Rev Latinoam Microbiol
]
Onchocerciasis is one of the major causes of blindness in the World, with about 17.7 million infected, particularly in West Africa. In Mexico, onchocerciasis is also present and has been subjected to control since 1923. The standard diagnosis of onchocerciasis is by the detection of microfilariae by skin biopsy and transmission is evaluated by detection of Onchocerca volvulus larvae in the vector. Classically, this was carried out by manual dissection of Simuliumn ochraceun s.l. However, with the use of ivermectin, a drug that kills microfilariae but not the adult worms, the skin biopsy is becoming no longer useful for detecting microfilariae levels and due to the reduced transmission, fly dissection is no longer viable. The subject of this paper is to present the immunological and molecular techniques developed to supersede the skin biopsy and fly dissection, and their diagnostic ability to assess the impact of multiple bi-annual mass ivermectin treatments on O. volvulus transmission in Mexico.
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Med Trop (Mars),
1998]
Two methods are being used to control onchocerciasis. The first has a delayed effect and consists in reducing or interrupting transmission of Onchocerca volvulus by eradication of the vector at its most vulnerable developmental stage, i.e. the larval stage. The second method has more immediate effects and consists in mass treatment using ivermectin, the only widely available drug, to reduce the density of microfilariae (the pathogenic stage of the parasite) in the population. Both strategies have been implemented within the framework of two international programs: the Onchocerciasis Control Program (OCP) in West Africa, which started in 1974 and will continue until the end of 2002, and the African Program for Onchocerciasis Control (APOC), which was launched in 1995 and will last for 12 years. This article presents an overview of the efficacy of available control tools, as well as the objectives, strategies, organization, and results of the two ongoing control programs. Also dealt with are future perspectives of onchocerciasis control including monitoring techniques to maintain OCP gains, and research to develop new control tools and optimize the program efficacy.
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Clin Microbiol Rev,
1999]
Onchocerciasis is a major cause of blindness. Although the World Health Organization has been successful in reducing onchocerciasis as a public health problem in parts of West Africa, there remain an estimated 17 million people infected with Onchocerca volvulus, the parasite that causes this disease. Ocular pathology can be manifested in any part of the eye, although disease manifestations are frequently characterized as either posterior or anterior eye disease. This review focuses on onchocerca-mediated keratitis that results from an inflammatory response in the anterior portion of the eye and summarizes what is currently known about human disease. This review also describes studies with experimental models that have been established to determine the immunological mechanisms underlying interstitial keratitis. The pathogenesis of keratitis is thought to be due to the host inflammatory response to degenerating parasites in the eye; therefore, the primary clinical symptoms of onchocercal keratitis (corneal opacification and neovascularization) are induced after injection of soluble O. volvulus antigens into the corneal stroma. Experimental approaches have demonstrated an essential role for sensitized T helper cells and shown that cytokines can regulate the severity of keratitis by controlling recruitment of inflammatory cells into the cornea. Chemokines are also important in inflammatory cell recruitment to the cornea, and their role in onchocerciasis is being examined. Further understanding of the molecular basis of the development of onchocercal keratitis may lead to novel approaches to immunologically based intervention.
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J Am Optom Assoc,
1993]
Onchocerciasis is commonly known as River Blindness and affects about 18 million people around the world. It is transmitted by black flies that breed in river and stream rapids and transmit the parasitic microfilariae, Onchocerca volvulus, to people who live and work near such rivers. Infection with the microfilariae results in blindness or visual impairment for 1 or 2 million people. The microfilariae migrate to superficial tissues and may invade any part of the eye and ocular structure. Living worms cause little damage, however, their death triggers a localized inflammation which can lead to blindness. Sclerosing keratitis, a severe corneal involvement, is the major cause of blindness from the disease. The World Health Organization (WHO) Expert Committee on Onchocerciasis has estimated that 9% of the disease is found in Africa, the rest occur in Yemen and Latin America. Treatment with ivermectin is contraindicated for pregnant and lactating women, children under 5 years of age, asthmatics, and people with other diseases. The WHO Onchocerciasis Control Program in 11 countries of West Africa has eliminated the risk of onchocerciasis by aerial spraying of black fly breeding sites only from 1 country. A single annual oral dose (150 mg/kg) of ivermectin can reverse early lesions in the cornea. Ivermectin must be taken annually to sustain protection against blindness, thus its incorporation into primary health care along with malaria, AIDS, trachoma, xerophthalmia, and cataract is most cost effective. Nigeria and Tanzania have optometry schools, and optometrists can play a significant role in onchocerciasis control and blindness prevention programs by training local health care workers to distribute invermectin in vision screening programs.
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Parasite,
2002]
Initially planned for a 20 year life time, the Onchocerciasis Control Programme in West Africa (OCP) will have finally continued its activities for nearly three decades (vector control alone from 1975 to 1989, then vector control and/or therapeutic treatment until 2002). Although onchocerciasis is no longer a problem of public health importance nor an obstacle to socio-economic development in the OCP area, the control of this filariasis is not over because OCP never aimed at eradication, neither of the parasite (Onchocerca volvulus), nor of its vector (Simulium damnosum s.l.). In 2003, the eleven Participating countries of OCP will take over the responsibility of carrying out the residual activities of monitoring and the control of this disease. This mission is of great importance because any recrudescence of the transmission could lead in the long run to the reappearance of the clinical signs of onchocerciasis, if not its most serious manifestations. For epidemiological and operational reasons, and given the disparity in national health policies and infrastructures, the capacities of the countries to take over the residual activities of monitoring and control of onchocerciasis are very unequal. Indeed, the interventions to be carried out are very different from one country to another and the process of integrating the residual activities into the national health systems is not taking place at the same pace. This inequality among the countries vis-a-vis the challenges to be met does not, however, prejudge the epidemiological situation after 2002 whose evolution will also depend on the effectiveness of the provisions made before that date by OCP, then after 2002, by the Regional Office for Africa of the World Health Organization which is currently setting up a sub-regional multidisease surveillance centre.
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Acta Leiden,
1990]
Community trials were started to address questions concerning the safety of ivermectin during large scale treatment, its potential for transmission control, its effect in preventing ocular onchocercal disease, its acceptability and the organization of large scale treatment. A summary is presented of the major, latest results on the short-term epidemiological impact of large scale ivermectin treatment, as observed in eight community trials undertaken in the Onchocerciasis Control Programme in West Africa (OCP). Ivermectin treatment resulted in a 96%-99% reduction in the mean load of microfilariae (mf) in the skin in treated patients. The subsequent mf-repopulation of the skin was faster than in the clinical trials and after 12 months the mean loads had returned to more than 40% of the pre-treatment load. Ocular mf loads were also greatly reduced and a post-treatment regression of early lesions of the anterior segment of the eye was observed. The transmission of Onchocerca volvulus was reduced by some 60% during the first year after treatment in one trial but no additional reduction was observed after the second treatment round. These results, and other recent research findings, have been used to quantify an epidemiological model for the transmission and control of onchocerciasis. Preliminary results of computer simulations of the predicted long-term epidemiological impact of large scale ivermectin treatment indicate that ivermectin treatment may play a very important role in disease control but that it is unlikely to become a practical tool for transmission control in endemic foci. Ivermectin treatment appears to be the most appropriate method for control of recrudescence of infection in an area where the parasite reservoir has been virtually eliminated by vector control, such as in the core area of the OCP.