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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

Prevalence of onchocerciasis infection in the R. Gambia focus.
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pntd-0000497-g002: Prevalence of onchocerciasis infection in the R. Gambia focus.

Mentions: De Sole et al. [25],[26] have mapped the pre-control distribution and severity of onchocerciasis in the Western Extension of the OCP, including all of Senegal and western Mali. According to their results, the selected study areas along the River Gambia and the River Bakoye were the two areas with the highest level of onchocerciasis endemicity in Senegal and western Mali where there was a high risk of onchocercal blindness. Along the River Faleme there was also an appreciable risk of onchocercal blindness along the southern part of the river where the study site is located. All three study sites were mapped in detail by the OCP and figures 2a, 3a and 4a show for each of the sites the spatial distribution of the prevalence of infection before the start of control. Onchocerciasis was endemic throughout the study areas, and in each area there were several hyperendemic villages. In the River Gambia focus, 8 out of 22 surveyed villages had a CMFL>10 mf/s (range 12.0 to 48.1 mf/s) [26]. In the River Bakoye focus 5 out of 11 surveyed villages had a CMFL>10 mf/s (range 10.2 to 21.6 mf/s) and in the River Faleme focus this was the case for 3 out of 27 surveyed villages, which had CMFL's of 13.3, 16.0 and 21.0 mf/s respectively.


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)

Prevalence of onchocerciasis infection in the R. Gambia focus.
© Copyright Policy
Related In: Results  -  Collection

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

pntd-0000497-g002: Prevalence of onchocerciasis infection in the R. Gambia focus.
Mentions: De Sole et al. [25],[26] have mapped the pre-control distribution and severity of onchocerciasis in the Western Extension of the OCP, including all of Senegal and western Mali. According to their results, the selected study areas along the River Gambia and the River Bakoye were the two areas with the highest level of onchocerciasis endemicity in Senegal and western Mali where there was a high risk of onchocercal blindness. Along the River Faleme there was also an appreciable risk of onchocercal blindness along the southern part of the river where the study site is located. All three study sites were mapped in detail by the OCP and figures 2a, 3a and 4a show for each of the sites the spatial distribution of the prevalence of infection before the start of control. Onchocerciasis was endemic throughout the study areas, and in each area there were several hyperendemic villages. In the River Gambia focus, 8 out of 22 surveyed villages had a CMFL>10 mf/s (range 12.0 to 48.1 mf/s) [26]. In the River Bakoye focus 5 out of 11 surveyed villages had a CMFL>10 mf/s (range 10.2 to 21.6 mf/s) and in the River Faleme focus this was the case for 3 out of 27 surveyed villages, which had CMFL's of 13.3, 16.0 and 21.0 mf/s respectively.

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