Experimental studies on the transmission of Guatemalan and West African strains of Onchocerca volvulus by Simulium ochraceum, S. metallicum and S. callidum

Leon, Jorge; Duke, B. O. L.

doi:10.1016/0035-9203(66)90223-9

Cited by 61 publications

(42 citation statements)

References 9 publications

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“…The early work on Onchocerca-Simulium complexes in Africa was later extended to the Americas by way of investigations first in Guatemala (De Leon & Duke, 1966) and later in Venezuela (Duke, 1970).…”

Section: B the Situation In The Americasmentioning

confidence: 99%

Final report of the Conference on the eradicability of Onchocerciasis

2003

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Sixty-four experts from a variety of disciplines attended a Conference on the Eradicability of Onchocerciasis at The Carter Center, in Atlanta GA, held January 22-24, 2002. The Conference, which was organized by The Carter Center and the World Health Organization, with funding from the Bill & Melinda Gates Foundation, addressed the question: "Is onchocerciasis (River Blindness) eradicable with current knowledge and tools?" Former US President Jimmy Carter attended part of the final plenary proceedings on January 24.The Conference consisted of a series of presentations by invited expert speakers (Appendix C) and further deliberations in four workgroups (Appendix D) followed by plenary discussion of major conclusions. The presentations underlined epidemiological and entomological differences between onchocerciasis in Africa and the Americas. Whilst onchocerciasis in Africa covers extensive areas and is associated with striking human and fly population migrations and remarkably efficient black fly vectors, in the Americas onchocerciasis is found in limited foci. Human and fly population migration are not major problems in the Americas, where most black fly species are inefficient, though some efficient black flies are also found there. Vector control has been effectively applied in the Onchocerciasis Control Program in West Africa (OCP) with remarkable results, interrupting transmission in most parts of the original Program area. The use of ivermectin has given variable results: while ivermectin treatment has been effective in all endemic areas in controlling onchocerciasis as a public health problem, its potential for interrupting transmission is more promising in hypo-and mesoendemic areas. The African Program for Onchocerciasis Control (APOC), which supports onchocerciasis control in endemic African countries outside the OCP, applies ivermectin, its principal control tool, to communities in high-risk areas as determined by rapid epidemiological mapping of onchocerciasis (REMO) and Geographic Information Systems (GIS). In the Americas, through support of the Onchocerciasis Elimination Program in the Americas (OEPA), a strategy of bi-annual ivermectin treatment of at least 85% of the eligible populations in all endemic communities is showing very good results and promises to be effective in eliminating onchocerciasis in the region.The Conference concluded that onchocerciasis is not eradicable using current tools due to the major barriers to eradication in Africa. However, the Conference also concluded that in most if not all the Americas, and possibly Yemen and some sites in Africa, transmission of onchocerciasis can be eliminated using current tools. The Conference recommended that where interruption of transmission is feasible and cost effective, programs should aim for that goal using all appropriate and available interventions so that the Onchocerca volvulus can eventually be eliminated and interventions halted. Although interruption of transmission of onchocerciasis cannot currently be achieved in mos...

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Section: B the Situation In The Americasmentioning

confidence: 99%

Final report of the Conference on the eradicability of Onchocerciasis

2003

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“…These differences will be further explored in the light of parasite-induced vector mortalities elsewhere. Elevated fly mortalities, following the ingestion of large numbers of parasites, have been reported to affect the species without the ' protection' afforded by the cibarial teeth (Lewis, 1953;Duke, 1962Duke, a, 1966Omar & Garms, 1977;Takaoka et al 19846), in contrast to the lower death rates recorded for species with toothed fore-guts (De Leon & Duke, 1966;Collins et al 1977;Takaoka et al 1984a;Shelley et al 1987). However, the amount of parasite-related vector loss which really takes place in endemic areas will depend on how frequent is the acquisition of high parasite intakes in the field.…”

Section: ( • ) S Damnosum Sl; ( • ) S Guianense (C)mentioning

confidence: 99%

“…This function may result in decreasing (negative feedback) or increasing (positive feed-back) rates of population growth as density rises. Although only negative feed-back processes are instrumental in Omar & Garms (1975) Collins et al (1977 De Leon & Duke (1966) Bain (1971) Philippon & Bain (1972) Philippon (1977 OCP ( constraining population growth, positive feed-back may also play a role in population dynamics by enhancing the chances of otherwise inefficient transmission mechanisms (Hairston & De Meillon, 1968). In the part of the life-cycle taking place in the vector host, density dependence may act on the elements of vector competence (Spielman & Rossignol, 1985;Dye 1992a).…”

Section: Introductionmentioning

confidence: 99%

Density-dependent processes in the transmission of human onchocerciasis: relationship between the numbers of microfilariae ingested and successful larval development in the simuliid vector

et al. 1995

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SUMMARYA previous paper reported that the intake of Onchocerca volvulus microfilariae (mff) by different species of Simulium is essentially proportional to the parasite load in the skin of infected carriers. This paper examines the fate of the ingested mff in susceptible vectors to assess the relationship between parasite intake and infective larval output in blackfly species with and without well-developed cibarial armatures. Analysis is based on data from 3 onchocerciasis endemic areas: /S. sirbanum) and the Amazonian focus between South Venezuela and Northern Brazil (S. guianense and S. oyapockense s.L).The data, which include published and unedited information collected in the field, record experimental studies of parasite uptake by wild flies maintained in captivity until the completion of the extrinsic incubation period. The relationship between L3 output (measured as the mean number of successful larvae/fly or, as the proportion of flies with infective larvae) and average microfilarial intake, was strongly non-linear. This non-linearity was best represented by a sigmoid function in case of armed simuliids (S. ochraceum s.L, S. oyapockense s.L), or by a hyperbolic expression in that of unarmed flies (S. damnosum s.L, S. guianense). These results are compatible, respectively, with the patterns of 'initial facilitation' and 'limitation' described in culicid vectors of lymphatic filariases. A maximum mean number of 1-3 L3/fly was observed in all 4 vectors. It is concluded that O. volvulus larval development to the infective stage is regulated by density-dependent mechanisms acting at the early phase of microfilarial migration out of the blackfly's bloodmeal. Damage by the bucco-pharyngeal armature may also be density dependent. A hypothesis, based on this density dependence is forwarded to explain initial facilitation, so far only recorded in vectors with well-developed cibarial teeth. Our results provide quantitative support for the conjecture that chemotherapy alone is likely to have a greater impact on reducing onchocerciasis transmission in endemic areas where the main vector has a toothed fore-gut than in foci where the vectors have unarmed cibaria.

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“…On the other hand, microfilarial densities derived from skin biopsies have been recognized as an important indicator of the intensity of infection in endemic areas of the disease. Microfilarial densities, however, differ in various areas of the skin of infected persons (DeLeon and Duke, 1966) and also varies with geographical differences of the disease as demonstrated by the World Health Organization Expert Committee (WHO, 1976). A better understanding of variation in microfilarial densities of O. volvulus in the skin would contribute to our epidemiological knowledge including diurnal or seasonal variations in densities.…”

mentioning

confidence: 99%

Guatemalan Onchocerciasis : Skin Snipping Methods and Microfilarial Densities in a Given Minute Area of the Skin

Zea¹,

Hashiguchi

Kawabata

et al. 1980

Jap. J. Trop. Med. Hyg.

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: To establish a convenient and reliable method for diagnosis and epidemiological surveys on Guatemalan onchocerciasis, three skin biopsy instruments were evaluated in 108 volunteers. The German-made Holth type, the Japan-made Walser type corneoscleral punches and a lancet and disposable scalpels were used for the purposes of taking skin snips. Better results were obtained with the lancet and scalpel, indicating a higher detection rate or a lower false negative rate for the patients. This method, however, showed some disadvantages in the present study. The volunteers had various complaints and/or rejected our examinations because of the painfulness of the scalpel procedure.On the other hand, the Holth punch was better than the Walser punch which indicated a relatively high false negative case and was rather troublesome in handling. From the results obtained, we recommend the Holth punch as the skin snip apparatus in Guatemala.To examine the microfilarial densities in a given minute area of the skin, six skin snips each (12 snips in total), 0.5 cm apart, were taken by the Holth punch from 33 subjects. In this study, there were considerable numbers of negative skin snips, especially in those patients who had a relatively low density of microfilariae. This would be of importance for diagnosis and epidemiological surveys for Guatemalan onchocerciasis. The results seem to indicate that if one skin snip was taken from the patients of a low endemic area in Guatemala, the prevalence of onchocerciasis in the area might be underestimated with false negative skin snips. Moreover, there was a great variation in the microfilarial densities in the 12 skin snips from each subject. The maximum to minimum rate of microfilarial densities in average was 1 : 9.7 in the left scapula and 1: 7.1 in the left iliac crest of the 33 subjects. These facts offer some useful suggestions for us, when we examine the intensity of infection in an endemic area or investigate a diurnal or seasonal variation of microfilarial densities of Onchocerca volvulus in Guatemala.

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Experimental studies on the transmission of Guatemalan and West African strains of Onchocerca volvulus by Simulium ochraceum, S. metallicum and S. callidum

Cited by 61 publications

References 9 publications

Final report of the Conference on the eradicability of Onchocerciasis

Final report of the Conference on the eradicability of Onchocerciasis

Density-dependent processes in the transmission of human onchocerciasis: relationship between the numbers of microfilariae ingested and successful larval development in the simuliid vector

Guatemalan Onchocerciasis : Skin Snipping Methods and Microfilarial Densities in a Given Minute Area of the Skin

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