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Feasibility of onchocerciasis elimination with ivermectin treatment in endemic foci in Africa: first evidence from studies in Mali and Senegal.

Diawara L, Traoré MO, Badji A, Bissan Y, Doumbia K, Goita SF, Konaté L, Mounkoro K, Sarr MD, Seck AF, Toé L, Tourée S, Remme JH - PLoS Negl Trop Dis (2009)

Bottom Line: This study has provided the first empirical evidence that elimination of onchocerciasis with ivermectin treatment is feasible in some endemic foci in Africa.Although further studies are needed to determine to what extent these findings can be extrapolated to other endemic areas in Africa, the principle of elimination has been established.The African Programme for Onchocerciasis Control has adopted an additional objective to assess progress towards elimination endpoints in all onchocerciasis control projects and to guide countries on cessation of treatment where feasible.

View Article: PubMed Central - PubMed

Affiliation: Ministère de Santé et de Prévention Médicale, Dakar, Senegal.

ABSTRACT

Background: Mass treatment with ivermectin is a proven strategy for controlling onchocerciasis as a public health problem, but it is not known if it can also interrupt transmission and eliminate the parasite in endemic foci in Africa where vectors are highly efficient. A longitudinal study was undertaken in three hyperendemic foci in Mali and Senegal with 15 to 17 years of annual or six-monthly ivermectin treatment in order to assess residual levels of infection and transmission and test whether ivermectin treatment could be safely stopped in the study areas.

Methodology/principal findings: Skin snip surveys were undertaken in 126 villages, and 17,801 people were examined. The prevalence of microfilaridermia was <1% in all three foci. A total of 157,500 blackflies were collected and analyzed for the presence of Onchocerca volvulus larvae using a specific DNA probe, and vector infectivity rates were all below 0.5 infective flies per 1,000 flies. Except for a subsection of one focus, all infection and transmission indicators were below postulated thresholds for elimination. Treatment was therefore stopped in test areas of 5 to 8 villages in each focus. Evaluations 16 to 22 months after the last treatment in the test areas involved examination of 2,283 people using the skin snip method and a DEC patch test, and analysis of 123,000 black flies. No infected persons and no infected blackflies were detected in the test areas, and vector infectivity rates in other catching points were <0.2 infective flies per 1,000.

Conclusion/significance: This study has provided the first empirical evidence that elimination of onchocerciasis with ivermectin treatment is feasible in some endemic foci in Africa. Although further studies are needed to determine to what extent these findings can be extrapolated to other endemic areas in Africa, the principle of elimination has been established. The African Programme for Onchocerciasis Control has adopted an additional objective to assess progress towards elimination endpoints in all onchocerciasis control projects and to guide countries on cessation of treatment where feasible.

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Related in: MedlinePlus

Location of the three study areas in Mali and Senegal.
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pntd-0000497-g001: Location of the three study areas in Mali and Senegal.

Mentions: The three study areas are located along the River Bakoye in Mali, the River Gambia in Senegal, and the River Faleme on the border of the two countries (figure 1). The study areas were selected on the basis of the following criteria: (i) they were part of the Western Extension area of the OCP where onchocerciasis control has been exclusively based on ivermectin treatment; (ii) ivermectin treatment started in 1988–1989 and the area was part of the first large-scale ivermectin treatment programs launched after registration of the drug in 1987; (iii) there existed good epidemiological baseline data for at least 10 villages where pre-control skin snip surveys had been undertaken by the OCP using standard onchocerciasis survey methods; (iv) the area contained hyperendemic villages, i.e. villages with a prevalence of microfilaridermia ≥60% or a Community Microfilarial Load (CMFL, the geometric mean number of microfilariae per skin snip among adults aged 20 years and above) >10 microfilariae per skin snip (mf/s) [22]–[24]; (v) the area was located along a river with known breeding sites of Simulium damnosum s.l., and has a length of at least 100 kilometers along the river and a width of at least 15 km at each side of the river. All three selected study areas met these criteria. An additional reason for including the River Gambia area was that it was the only area in Africa where six-monthly treatment with ivermectin had been given for more than 10 years. Demographically, the three study areas were similar with a rural population in 2006 of 20,000 to 30,000 people living in 75 to 94 villages per site (table 1). In the R. Gambia focus there is also one town with a population of about 18,000 but there are no urban settlements in the other two study areas.


Feasibility of onchocerciasis elimination with ivermectin treatment in endemic foci in Africa: first evidence from studies in Mali and Senegal.

Diawara L, Traoré MO, Badji A, Bissan Y, Doumbia K, Goita SF, Konaté L, Mounkoro K, Sarr MD, Seck AF, Toé L, Tourée S, Remme JH - PLoS Negl Trop Dis (2009)

Location of the three study areas in Mali and Senegal.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2710500&req=5

pntd-0000497-g001: Location of the three study areas in Mali and Senegal.
Mentions: The three study areas are located along the River Bakoye in Mali, the River Gambia in Senegal, and the River Faleme on the border of the two countries (figure 1). The study areas were selected on the basis of the following criteria: (i) they were part of the Western Extension area of the OCP where onchocerciasis control has been exclusively based on ivermectin treatment; (ii) ivermectin treatment started in 1988–1989 and the area was part of the first large-scale ivermectin treatment programs launched after registration of the drug in 1987; (iii) there existed good epidemiological baseline data for at least 10 villages where pre-control skin snip surveys had been undertaken by the OCP using standard onchocerciasis survey methods; (iv) the area contained hyperendemic villages, i.e. villages with a prevalence of microfilaridermia ≥60% or a Community Microfilarial Load (CMFL, the geometric mean number of microfilariae per skin snip among adults aged 20 years and above) >10 microfilariae per skin snip (mf/s) [22]–[24]; (v) the area was located along a river with known breeding sites of Simulium damnosum s.l., and has a length of at least 100 kilometers along the river and a width of at least 15 km at each side of the river. All three selected study areas met these criteria. An additional reason for including the River Gambia area was that it was the only area in Africa where six-monthly treatment with ivermectin had been given for more than 10 years. Demographically, the three study areas were similar with a rural population in 2006 of 20,000 to 30,000 people living in 75 to 94 villages per site (table 1). In the R. Gambia focus there is also one town with a population of about 18,000 but there are no urban settlements in the other two study areas.

Bottom Line: This study has provided the first empirical evidence that elimination of onchocerciasis with ivermectin treatment is feasible in some endemic foci in Africa.Although further studies are needed to determine to what extent these findings can be extrapolated to other endemic areas in Africa, the principle of elimination has been established.The African Programme for Onchocerciasis Control has adopted an additional objective to assess progress towards elimination endpoints in all onchocerciasis control projects and to guide countries on cessation of treatment where feasible.

View Article: PubMed Central - PubMed

Affiliation: Ministère de Santé et de Prévention Médicale, Dakar, Senegal.

ABSTRACT

Background: Mass treatment with ivermectin is a proven strategy for controlling onchocerciasis as a public health problem, but it is not known if it can also interrupt transmission and eliminate the parasite in endemic foci in Africa where vectors are highly efficient. A longitudinal study was undertaken in three hyperendemic foci in Mali and Senegal with 15 to 17 years of annual or six-monthly ivermectin treatment in order to assess residual levels of infection and transmission and test whether ivermectin treatment could be safely stopped in the study areas.

Methodology/principal findings: Skin snip surveys were undertaken in 126 villages, and 17,801 people were examined. The prevalence of microfilaridermia was <1% in all three foci. A total of 157,500 blackflies were collected and analyzed for the presence of Onchocerca volvulus larvae using a specific DNA probe, and vector infectivity rates were all below 0.5 infective flies per 1,000 flies. Except for a subsection of one focus, all infection and transmission indicators were below postulated thresholds for elimination. Treatment was therefore stopped in test areas of 5 to 8 villages in each focus. Evaluations 16 to 22 months after the last treatment in the test areas involved examination of 2,283 people using the skin snip method and a DEC patch test, and analysis of 123,000 black flies. No infected persons and no infected blackflies were detected in the test areas, and vector infectivity rates in other catching points were <0.2 infective flies per 1,000.

Conclusion/significance: This study has provided the first empirical evidence that elimination of onchocerciasis with ivermectin treatment is feasible in some endemic foci in Africa. Although further studies are needed to determine to what extent these findings can be extrapolated to other endemic areas in Africa, the principle of elimination has been established. The African Programme for Onchocerciasis Control has adopted an additional objective to assess progress towards elimination endpoints in all onchocerciasis control projects and to guide countries on cessation of treatment where feasible.

Show MeSH
Related in: MedlinePlus