Produção Nacional
Revisado por pares
The onchocerciasis chronicle: from the beginning to the end?
2012; Elsevier BV; Volume: 28; Issue: 7 Linguagem: Inglês
10.1016/j.pt.2012.04.005
ISSN1471-5007
AutoresAndy Crump, Carlos Morel, Satoshi Ōmura,
Tópico(s)Parasites and Host Interactions
ResumoThe year 2012 marks the 25th anniversary of the donation of ivermectin to fight onchocerciasis and the projected date for elimination of transmission of the disease in the Americas. This review looks at the history of onchocerciasis, from its discovery through to 2025, by which time it is projected that the disease will have been eliminated as a public health problem, except in a handful of sub-Saharan countries, where it should be well on the way towards elimination. The year 2012 marks the 25th anniversary of the donation of ivermectin to fight onchocerciasis and the projected date for elimination of transmission of the disease in the Americas. This review looks at the history of onchocerciasis, from its discovery through to 2025, by which time it is projected that the disease will have been eliminated as a public health problem, except in a handful of sub-Saharan countries, where it should be well on the way towards elimination. In 1945, the renowned ophthalmologist Sir Harold Ridley wrote, "…it is inconceivable that, in the end, science will be defeated by a filaria". The words appeared at the end of a seminal article he published on onchocerciasis (river blindness), a parasitic disease prevalent throughout tropical Africa for centuries [1Ridley N.H.L. Ocular onchocerciasis: including an investigation in the Gold Coast.Br. J. Ophthalmol. 1945; 29: 1-58PubMed Google Scholar]. He may soon be proved correct, for the fight to control onchocerciasis, which has been progressing since 1946 and became truly international and gathered momentum since 1974, has been pioneering, innovative and highly successful, a model for others to follow. The long-term efforts at onchocerciasis control, together with sustained political commitment of national governments, bilateral donors, and non-governmental development organisations (NGDOs) and affected communities themselves, is a major, yet relatively unheralded public health and development success story. Investments in onchocerciasis control also provide one of the highest economic rates of return of all international development initiatives, some 15–20% [2Hodgkin C. et al.The future of onchocerciasis control in Africa.PLoS Negl. Trop. Dis. 2007; 1: e74Crossref PubMed Scopus (25) Google Scholar]. The year 2012 marks the 25th anniversary of the global donation of a curative drug, ivermectin, for as long as it is needed, as well as being the target date for eliminating onchocerciasis from the Americas, and evidence has recently emerged that it may well be possible to eliminate the disease from its origins in Africa using mass administration of ivermectin. Unsurprisingly, onchocerciasis control has been labelled 'one of the most triumphant public health campaigns ever waged in the developing world' [3Gaillard, J. et al. (2005) Africa. In UNESCO, World Science Report, pp. 177–202, UNESCOGoogle Scholar]. Onchocerciasis is prevalent throughout many major river basins in Africa, the traditional homes of the rural, subsistence farming population of the continent. It is also called river blindness because the blood-feeding flies that transmit the ultimately blinding disease inhabit lush, fertile land alongside the rivers in which they breed. Onchocerciasis was first scientifically observed almost 140 years ago, despite it having been around for centuries. Subsequently, scientists recognised that humans develop the disease after being bitten by vector blackflies of the genus Simulium (Box 1) that were carrying infective larvae of a filarial threadworm parasite, Onchocerca volvulus (Box 2). Some 13 million km2 of the earth became covered by the disease, with infection rates varying considerably depending on altitude, rainfall levels, latitude and environmental factors affecting the breeding of the insect vector. More than 99% of people infected with O. volvulus live in sub-Saharan Africa. Following the independence of South Sudan, the disease (Box 3) affects 31 African nations, with Nigeria accounting for 25% of the total global infection. It was also inadvertently introduced into other parts of the world through human activity, the locations being Yemen and six Latin American nations, Brazil, Colombia, Ecuador, Guatemala, Mexico and Venezuela [4World Health Organization First WHO Report on Neglected Tropical Diseases: Working to Overcome the Global Impact of Neglected Tropical Diseases. WHO, 2010Google Scholar]. Other forms of onchocerciasis affect various animals, including wild game, livestock, draught animals and dogs.Box 1The vectorIn tropical Africa, Onchocerca parasites are transmitted primarily by Dipteran blackflies of the Simulium damnosum complex, members of the Simulium neavei group also being vectors. Some game animals, notably elands and buffalo, are possible reservoir hosts, which, if true, will make disease eradication in places where these animals exist impractical [1Ridley N.H.L. Ocular onchocerciasis: including an investigation in the Gold Coast.Br. J. Ophthalmol. 1945; 29: 1-58PubMed Google Scholar]. In the Western hemisphere, varieties of Simulium species bite humans and may transmit parasites.Female blackflies require a bloodmeal to develop their eggs. When the fly bites, microfilarial parasites move towards the bite site, are ingested, and undergo development in the insect vector. During a bloodfeed, the mandibles of the fly cut into the skin with rapid scissor-like movements causing blood to pool, the blood being sucked by cibarial and pharyngeal pumps, with blood-feeding usually taking 4–5 min (http://www.blackfly.org.uk/simbiol2.html). The bites can be an entry point for any pathogens that the flies carry or which exist in the environment [67Ubachukwu P.O. Human onchocerciasis: epidemiological status of Uzo-Uwari local government area of Enugu State Nigeria.Nig. J. Parasitol. 2004; 25: 93-99Google Scholar, 68Usip L.P.E. et al.Longitudinal evaluation of repellent activity of Ocimium gratissimum (Labiatae) volatile oil against Simulium damnosum.Mem. Inst. Oswaldo Cruz. 2006; 101: 201-205Crossref PubMed Scopus (22) Google Scholar]. Infected female flies deposit infective Onchocerca larvae, which enter the human body.Female blackflies lay their eggs (in batches of 200–300) on vegetation in rapid flowing, turbulent, well-oxygenated streams and rivers up to 1400 m in elevation. In 2–3 weeks the eggs develop into aquatic larvae, attaching themselves to plant stems or rocks just below the water surface, before developing into the adult form, the process occurring in as little as 6 weeks.Adult blackflies usually remain close to the watercourse where they emerge, although they can travel vast distances borne on prevailing winds, with studies showing that S. damnosum can invade land up to 400 km from their origin. Prone to desiccation, the flies are photophobic, sheltering in grass and locating a human host when they walk past; flies usually feed during cooler hours of early morning or late afternoon (coinciding with active farming periods). Their riverine ecological and behavioural peculiarities mean they infest the most fertile land available.Repeated infective bites, sometimes over many months, cause infection – in hyperendemic areas, one person may suffer several thousand bites a day. The consequence is an overall lowering of productivity, ill health, disfigurement and often abandonment of infested areas, devastating socioeconomic wellbeing in affected communities. Recent reports indicate that the cost to individual families in Africa can be catastrophic with poor subsistence farmers in Nigeria spending half of their annual income to treat ailments associated with blackfly bites [69Adeleke M.A. et al.Socioeconomic implications of Simulium damnosum complex infestation in some rural communities in Odeda local government area of Ogun State,Nigeria.J. Public Health Epidemiol. 2010; 2: 109-112Google Scholar]. Blackfly bites have also accounted for reduced tourism and deaths in wild animals and livestock [70Currie D.C. Adler P.H. Global diversity of blackflies (Diptera, Simuliidae) in fresh water.Hydrobiologia. 2008; 595: 469-475Crossref Scopus (64) Google Scholar].Box 2The parasiteO. volvulus has not been transmitted experimentally to humans by infected flies, but epidemiological evidence suggests that the prepatent period between inoculum and appearance of microfilariae is between 3 and 18 months, being most commonly around 15 months [71Duke B.O.L. Experimental transmission of Onchocerca volvulus to chimpanzees.Trans. R. Soc. Trop. Med. Hyg. 1962; 56: 271Google Scholar]. Once in the human body, infective larvae, which mature in around 12 months but can exist for 14 years, develop into adult worms which then mate. Adult male and female worms, usually paired, are predominantly found in fibrous subcutaneous nodules or cysts. The nodules, which feel like rubber, do not cause pain or tenderness. They are commonly found over a bony area, usually over the ribs and iliac crests in Africa and on the forehead in the Americas. Nodule size varies (generally being smaller in the Americas), as do the numbers on any individual, the highest recorded being 126. The nearer the nodule is to the eye, the greater the chance of ocular involvement. The nodules usually contain more than one pair of worms, commonly intertwined, as well as several single males, which are considerably smaller than the females (which can be up to 300 mm in length). Reproduction is ovoviviparous, with females producing embryonic microfilariae, often in excess of 1000 daily. The reproductive lifespan of a female is 14–15 years. Adult worms may live for 15 years and can produce microfilariae for up to 10 years [72Roberts J.M. et al.Onchocerciasis in Kenya 9, 11 and 18 years after elimination of the vector.Bull. WHO. 1967; 37: 195-212PubMed Google Scholar], whereas microfilariae live for 6 months to 3 years [73Duke B.O.L. The intake and transmissibility of Onchocerca volvulus microfilariae by Simulium damnosum fed on patients treated with Diethylcarbamazine, Suramin or Mel W.Bull. WHO. 1968; 39: 169-178PubMed Google Scholar]. Microfilariae of the African and American worms are indistinguishable. They migrate primarily to the skin, mammary glands, eye and lymph glands but are not usually found in the blood. Thousands of microfilariae eventually die, stimulating the immune system of the host and provoking the inflammatory tissue reactions responsible for symptoms of the disease.Box 3The diseaseIn humans, infection can lead to severe visual impairment, including permanent blindness. Immature Onchocerca worms (microfilariae) enter virtually every part of the eye, except the lens, and cause inflammation, bleeding and other complications. The result is impaired vision and, eventually, blindness from corneal opacities, complicated cataract, choridoretinal degeneration and optic atrophy, with a tendency for bilateral symmetry leading to both eyes being damaged. Of perhaps greater significance, infection also results in the formation of skin nodules and onchocercal skin disease, which is manifest in skin lesions that cause severe itching, dermatitis and depigmentation, which can culminate in gross and stigmatising skin disfigurement. Skin lesions are widespread, numerous and readily visible, being named 'leopard skin' and 'elephant skin'. The skin becomes dry and wrinkled, losing its elasticity, causing those affected to look much older than their age. It is believed that skin lesions and ocular complications are caused by the immune response of the host to the dead parasites, live microfilariae inducing no such response. However, living adult worms do stimulate a reticuloendothelial response which helps form the fibrous nodules in which they dwell [1Ridley N.H.L. Ocular onchocerciasis: including an investigation in the Gold Coast.Br. J. Ophthalmol. 1945; 29: 1-58PubMed Google Scholar]. Unrelenting itching alone is estimated to account for 60% of the disease burden, and onchocerciasis has also been shown to curtail life expectancy by up to 15 years [4World Health Organization First WHO Report on Neglected Tropical Diseases: Working to Overcome the Global Impact of Neglected Tropical Diseases. WHO, 2010Google Scholar]. The socioeconomic costs of the disease to a nation are known to be in the tens of millions annually.Recently, there has been an increasing and, as yet unexplained, association between onchocerciasis and some mental conditions, especially in children. In Uganda, since the 1960s, onchocerciasis infection has been linked with Nakalanga syndrome, a hyposexual dwarfism usually associated with dental caries and mental disturbances. Elsewhere in parts of Africa where onchocerciasis and epilepsy occur together, and where belief in spirits is deep-rooted, there is an anecdotal link between the two [74Kipp W. et al.The Nakalanga syndrome in Kabarole District, Western Uganda.Am. J. Trop. Med. Hyg. 1996; 54: 80-83PubMed Google Scholar, 75Crump A. Outstanding, innovative disease control solution meets a minor hitch (TDR Photofeature 4).App. Tech. 2003; 30: 13-17Google Scholar].Nodding syndrome, a mysterious permanent neurologic condition is increasingly being reported from Sudan, Uganda and Tanzania. Although its aetiology and pathophysiology remain unknown, infected children (mainly 5–15 years old) exhibit epileptic-like seizures, impaired cognition and nod their heads constantly when they are given food. Most afflicted with Nodding syndrome also have antibodies for Onchocerca and live near rivers or fast-moving streams but no association has yet been proven. The disease is also associated with malnourishment and vitamin B6 deficiency [76Donnelly J. CDC planning trial for mysterious Nodding syndrome.Lancet. 2012; 379: 299Abstract Full Text Full Text PDF PubMed Scopus (14) Google Scholar]. In tropical Africa, Onchocerca parasites are transmitted primarily by Dipteran blackflies of the Simulium damnosum complex, members of the Simulium neavei group also being vectors. Some game animals, notably elands and buffalo, are possible reservoir hosts, which, if true, will make disease eradication in places where these animals exist impractical [1Ridley N.H.L. Ocular onchocerciasis: including an investigation in the Gold Coast.Br. J. Ophthalmol. 1945; 29: 1-58PubMed Google Scholar]. In the Western hemisphere, varieties of Simulium species bite humans and may transmit parasites. Female blackflies require a bloodmeal to develop their eggs. When the fly bites, microfilarial parasites move towards the bite site, are ingested, and undergo development in the insect vector. During a bloodfeed, the mandibles of the fly cut into the skin with rapid scissor-like movements causing blood to pool, the blood being sucked by cibarial and pharyngeal pumps, with blood-feeding usually taking 4–5 min (http://www.blackfly.org.uk/simbiol2.html). The bites can be an entry point for any pathogens that the flies carry or which exist in the environment [67Ubachukwu P.O. Human onchocerciasis: epidemiological status of Uzo-Uwari local government area of Enugu State Nigeria.Nig. J. Parasitol. 2004; 25: 93-99Google Scholar, 68Usip L.P.E. et al.Longitudinal evaluation of repellent activity of Ocimium gratissimum (Labiatae) volatile oil against Simulium damnosum.Mem. Inst. Oswaldo Cruz. 2006; 101: 201-205Crossref PubMed Scopus (22) Google Scholar]. Infected female flies deposit infective Onchocerca larvae, which enter the human body. Female blackflies lay their eggs (in batches of 200–300) on vegetation in rapid flowing, turbulent, well-oxygenated streams and rivers up to 1400 m in elevation. In 2–3 weeks the eggs develop into aquatic larvae, attaching themselves to plant stems or rocks just below the water surface, before developing into the adult form, the process occurring in as little as 6 weeks. Adult blackflies usually remain close to the watercourse where they emerge, although they can travel vast distances borne on prevailing winds, with studies showing that S. damnosum can invade land up to 400 km from their origin. Prone to desiccation, the flies are photophobic, sheltering in grass and locating a human host when they walk past; flies usually feed during cooler hours of early morning or late afternoon (coinciding with active farming periods). Their riverine ecological and behavioural peculiarities mean they infest the most fertile land available. Repeated infective bites, sometimes over many months, cause infection – in hyperendemic areas, one person may suffer several thousand bites a day. The consequence is an overall lowering of productivity, ill health, disfigurement and often abandonment of infested areas, devastating socioeconomic wellbeing in affected communities. Recent reports indicate that the cost to individual families in Africa can be catastrophic with poor subsistence farmers in Nigeria spending half of their annual income to treat ailments associated with blackfly bites [69Adeleke M.A. et al.Socioeconomic implications of Simulium damnosum complex infestation in some rural communities in Odeda local government area of Ogun State,Nigeria.J. Public Health Epidemiol. 2010; 2: 109-112Google Scholar]. Blackfly bites have also accounted for reduced tourism and deaths in wild animals and livestock [70Currie D.C. Adler P.H. Global diversity of blackflies (Diptera, Simuliidae) in fresh water.Hydrobiologia. 2008; 595: 469-475Crossref Scopus (64) Google Scholar]. O. volvulus has not been transmitted experimentally to humans by infected flies, but epidemiological evidence suggests that the prepatent period between inoculum and appearance of microfilariae is between 3 and 18 months, being most commonly around 15 months [71Duke B.O.L. Experimental transmission of Onchocerca volvulus to chimpanzees.Trans. R. Soc. Trop. Med. Hyg. 1962; 56: 271Google Scholar]. Once in the human body, infective larvae, which mature in around 12 months but can exist for 14 years, develop into adult worms which then mate. Adult male and female worms, usually paired, are predominantly found in fibrous subcutaneous nodules or cysts. The nodules, which feel like rubber, do not cause pain or tenderness. They are commonly found over a bony area, usually over the ribs and iliac crests in Africa and on the forehead in the Americas. Nodule size varies (generally being smaller in the Americas), as do the numbers on any individual, the highest recorded being 126. The nearer the nodule is to the eye, the greater the chance of ocular involvement. The nodules usually contain more than one pair of worms, commonly intertwined, as well as several single males, which are considerably smaller than the females (which can be up to 300 mm in length). Reproduction is ovoviviparous, with females producing embryonic microfilariae, often in excess of 1000 daily. The reproductive lifespan of a female is 14–15 years. Adult worms may live for 15 years and can produce microfilariae for up to 10 years [72Roberts J.M. et al.Onchocerciasis in Kenya 9, 11 and 18 years after elimination of the vector.Bull. WHO. 1967; 37: 195-212PubMed Google Scholar], whereas microfilariae live for 6 months to 3 years [73Duke B.O.L. The intake and transmissibility of Onchocerca volvulus microfilariae by Simulium damnosum fed on patients treated with Diethylcarbamazine, Suramin or Mel W.Bull. WHO. 1968; 39: 169-178PubMed Google Scholar]. Microfilariae of the African and American worms are indistinguishable. They migrate primarily to the skin, mammary glands, eye and lymph glands but are not usually found in the blood. Thousands of microfilariae eventually die, stimulating the immune system of the host and provoking the inflammatory tissue reactions responsible for symptoms of the disease. In humans, infection can lead to severe visual impairment, including permanent blindness. Immature Onchocerca worms (microfilariae) enter virtually every part of the eye, except the lens, and cause inflammation, bleeding and other complications. The result is impaired vision and, eventually, blindness from corneal opacities, complicated cataract, choridoretinal degeneration and optic atrophy, with a tendency for bilateral symmetry leading to both eyes being damaged. Of perhaps greater significance, infection also results in the formation of skin nodules and onchocercal skin disease, which is manifest in skin lesions that cause severe itching, dermatitis and depigmentation, which can culminate in gross and stigmatising skin disfigurement. Skin lesions are widespread, numerous and readily visible, being named 'leopard skin' and 'elephant skin'. The skin becomes dry and wrinkled, losing its elasticity, causing those affected to look much older than their age. It is believed that skin lesions and ocular complications are caused by the immune response of the host to the dead parasites, live microfilariae inducing no such response. However, living adult worms do stimulate a reticuloendothelial response which helps form the fibrous nodules in which they dwell [1Ridley N.H.L. Ocular onchocerciasis: including an investigation in the Gold Coast.Br. J. Ophthalmol. 1945; 29: 1-58PubMed Google Scholar]. Unrelenting itching alone is estimated to account for 60% of the disease burden, and onchocerciasis has also been shown to curtail life expectancy by up to 15 years [4World Health Organization First WHO Report on Neglected Tropical Diseases: Working to Overcome the Global Impact of Neglected Tropical Diseases. WHO, 2010Google Scholar]. The socioeconomic costs of the disease to a nation are known to be in the tens of millions annually. Recently, there has been an increasing and, as yet unexplained, association between onchocerciasis and some mental conditions, especially in children. In Uganda, since the 1960s, onchocerciasis infection has been linked with Nakalanga syndrome, a hyposexual dwarfism usually associated with dental caries and mental disturbances. Elsewhere in parts of Africa where onchocerciasis and epilepsy occur together, and where belief in spirits is deep-rooted, there is an anecdotal link between the two [74Kipp W. et al.The Nakalanga syndrome in Kabarole District, Western Uganda.Am. J. Trop. Med. Hyg. 1996; 54: 80-83PubMed Google Scholar, 75Crump A. Outstanding, innovative disease control solution meets a minor hitch (TDR Photofeature 4).App. Tech. 2003; 30: 13-17Google Scholar]. Nodding syndrome, a mysterious permanent neurologic condition is increasingly being reported from Sudan, Uganda and Tanzania. Although its aetiology and pathophysiology remain unknown, infected children (mainly 5–15 years old) exhibit epileptic-like seizures, impaired cognition and nod their heads constantly when they are given food. Most afflicted with Nodding syndrome also have antibodies for Onchocerca and live near rivers or fast-moving streams but no association has yet been proven. The disease is also associated with malnourishment and vitamin B6 deficiency [76Donnelly J. CDC planning trial for mysterious Nodding syndrome.Lancet. 2012; 379: 299Abstract Full Text Full Text PDF PubMed Scopus (14) Google Scholar]. Although not proven, it is generally accepted that disease foci outside Africa are the consequence of accidental introduction of the parasite, almost certainly due to infected individuals being transported via the slave trade [5Ruiz Reyes F. Datos historicos sobre el origen de la onchocercosis en America.Rev. Méd. Mex. 1952; 32: 49-56Google Scholar]. A recent United Nations Educational, Scientific and Cultural Organization (UNESCO) analysis concluded that 15–18 million captives were involved in the Trans-Atlantic trade alone (not including those who died en route). More than half toiled in sugarcane plantations in the Caribbean and Brazil [6UNESCO Struggles against Slavery. UNESCO, 2004http://unesdoc.unesco.org/images/0013/001337/133738e.pdfGoogle Scholar]. An estimated 40% of the total went to Brazil, which, in 1888, was the last of the New World territories to abolish slavery. Most of the slaves transported in the Trans-Atlantic trade originated in areas of Africa where onchocerciasis was endemic (Figure 1a–d), with the current distribution of the disease reflecting the destination of slaves. The 2007 bicentennial of the abolition of the slave trade drew attention to the legacy of slavery, especially its inhuman and socially devastating consequences, as well as its detrimental public health impact. Transportation of millions of slaves facilitated introduction of a range of parasitic diseases to the Americas which persist today, including onchocerciasis [7Grove D.I. A History of Human Helminthology. CAB International, 1990Google Scholar, 8Lammie P. et al.Eliminating lymphatic filariasis, onchocerciasis, and schistosomiasis from the Americas: breaking a historical legacy of slavery.PLoS Negl. Trop. Dis. 2007; 1: e71Crossref PubMed Scopus (22) Google Scholar]. The introduction of the causative parasites, coupled with the presence of competent vectors, allowed the imported diseases to be transmitted in the new environments, a view first espoused by parasitologists more than a century ago [9Manson P. Report of a case of Bilharzia from the West Indies.Br. Med. J. 1902; ii: 1894-1895Crossref Scopus (16) Google Scholar]. Compelling evidence supporting this hypothesis has only relatively recently appeared, for example, molecular studies of O. volvulus finding very limited heterogeneity in New World strains, but discovering that they share a strong affinity with West African strains [10Zimmerman P.A. et al.Recent evolutionary history of American Onchocerca volvulus, based on analysis of a tandemly repeated DNA sequence family.Mol. Biol. Evol. 1994; 11: 384-392PubMed Google Scholar]. 1874. John O'Neill, a British naval surgeon based in the Gold Coast (now Ghana) was intrigued by an irritating and intractable skin disease afflicting many locals. Similar to scabies, it was known locally as 'kra kra' or 'craw–craw'. Microscopic examination of specimens taken from papules of patients showed easily visible, minute worms that contorted violently. O'Neill recorded "at the head, or blunted extremity, two small dots are noticed, but their nature could not be determined" [11O'Neil J. On the presence of a filarial in "craw craw".Lancet. 1875; i: 265-266Abstract Scopus (19) Google Scholar]. This proved to be the first observation of the microfilaria of O. volvulus. 1890. An unknown German surgeon in the Gold Coast excised two lumps (nodules), each the size of the egg of a small bird, from the scalp and the chest of two locals. Discovering the nodules contained worms, he sent them to Rudolf Leuckart in Germany for identification. Leuckart found several female and male worms in each nodule, the females being 6–70 mm in length and the males approximately half that size, all coiled together in a compact ball. The worm mass was in a cavity containing fluid laden with embryos. Leuckart did not announce his discovery, but informed the renowned British parasitologist Sir Patrick Manson. Manson subsequently published a brief note, acknowledging Leuckart, labelling the parasite Filaria volvulus (from the Latin 'volvo, volvere' meaning to roll or turn round) [12Davidson A. Hygiene and Diseases of Warm Climates. Young J. Pentland, 1893Google Scholar]. 1899. Labadie-Lagrave and Deguy removed a female worm from a nodule on a French soldier who had returned from West Africa and identified it as F. volvulus [13Labadie-Lagrave F. Deguy F. Un cas de Filaria volvulus.Arch. Parasitol. 1899; 2: 451-460Google Scholar]. 1901. The first detailed descriptions of adult worms (male and female) and microfilariae were published [14Prout W.T. A filarial found in Sierra Leone – Filaria volvulus (Leuckart).Br. Med. J. 1901; i: 209-211Crossref Scopus (5) Google Scholar]. 1910. Raillet and Henry transferred the parasite from the genus Filaria to the genus Onchocerca, which had been erected by Diesing in 1841. The name Onchocerca was derived from a combination of the Greek word 'Onchos' meaning 'hook' and 'Kerkos' or 'Cercos' meaning 'tail' [15Railliet A. Henry A.C. Remarques à l'occasion de la note de M. le Dr. Antoine.Bull. Soc. Pathol. Exot. Filiales. 1910; 3: 91-93Google Scholar]. Humans are the only definitive host for O. volvulus. 1913. Ouzilleau published the first report of patients with onchocercal nodules [16Ouzilleau F. Les filaires dumaines de la Région du M'Bomou (Afrique équatoriale française). Pathogénie de l'éléphantiasis de cette region. Rôle de la Filaria volvulus.Bull. Soc. Pathol. Exot. Filiales. 1913; 7: 80-88Google Scholar]. 1915. Ocular onchocerciasis was first identified by Robles and Pacheco-Luna in Guatemala. Robles encountered a patient with erysipelas of the face accompanied by fever, pruritus and poor vision but could not identify any cause. He subsequently examined a boy with identical symptoms who also had oedema of the eyelids, the forehead, and upper lip and who displayed a cherry-sized nodule on his forehead. Robles excised the nodule and discovered the first adult Onchocerca in the Americas, reporting, "I understood then that the erysipelas lesions surely were due to the presence of this parasite" [17Robles R. Enfermedad nueva en Guatemala.La Juventud Médica. 1917; 17: 97-115Google Scholar]. He later postulated that Simulium flies might be the vector of the parasites and that there was a link between infection and eye disease [18Robles R. Onchocercose humaine au Guatémala produisant la cêcité et "l'érysipéle du littoral" (Erisipela de la costa).Bull. Soc. Pathol. Exot. Filiales. 1919; 12: 442-460Google Scholar]. 1919. The worm in the Americas was designated Onchocerca caecutiens (the blinding filaria) by Brumpt [19Brumpt E. Une nouvelle filaire pathogèn e parasite de l'homme (Onchocerca caecutiens, n. sp.).Bull. Soc. Pathol. Exot. Filiales. 1919; 12: 464-473Google Scholar]. Calderon posited that eye lesions were caused by toxins rele
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