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--- Onchocerciasis elimination in endemic foci

Thursday, 1st of November 2012

• ONCHOCERCIASIS ELIMINATION IN ENDEMIC FOCI

‘[O]nchocerciasis elimination with ivermectin treatment is feasible in at least some endemic foci in Africa.’

Proof-of-Principle of Onchocerciasis Elimination with Ivermectin Treatment in Endemic Foci in Africa: Final Results of a Study in Mali and Senegal

Author Summary

The control of onchocerciasis, or river blindness, is based on annual or six-monthly treatment with ivermectin of populations at risk. This has been effective in controllingthe disease as a public health problem but it was not known whether it could also eliminate infection andtransmission to the extent that treatment could be safely stopped. Many doubted that this was feasible in Africa. Astudy was undertaken in three hyperendemic onchocerciasis foci with seasonal transmission in Mali and Senegalwhere treatment has been given for 15 to 17 years. As a result of this treatment, infection and transmission levelshad fallen everywhere below postulated thresholds for elimination. Treatment was therefore stopped in eachfocus. Follow-up evaluations up to 5 years after the last treatment showed no evidence of recrudescence afterstopping treatment but instead a consistent decline in infection and transmission levels, reaching zero in twosites. The study has established the proof-of-principle that onchocerciasis elimination with ivermectin treatment isfeasible in at least some endemic foci in Africa. The results of the study have greatly contributed to the currentevolution from onchocerciasis control to elimination in Africa.

Mamadou O. Traore¹, Moussa D. Sarr², Alioune Badji², Yiriba Bissan³, Lamine Diawara², Konimba Doumbia¹, Soula F. Goita¹, Lassana Konate⁴, Kalifa Mounkoro¹, Amadou F. Seck², Laurent Toe³, Seyni Toure², Jan H. F. Remme^5*

1 Direction Nationale de la Santé, Bamako, Mali, 2 Ministere de la Santé et de la Prévention, Dakar, Senegal, 3 Multi-disease Surveillance Centre, Ouagadougou, Burkina Faso, 4 University Cheikh Anta Diop, Dakar, Senegal, 5 Ornex, France

Abstract below; full text, http://www.plosntds.org/article/info%3Adoi%2F10.1371%2Fjournal.pntd.0001825

Background

Mass treatment with ivermectin controls onchocerciasis as a public health problem, but it was not known if it could 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 treatment could be safely stopped. This article reports the results of the final evaluations up to 5 years after the last treatment.

Methodology/Principal Findings

Skin snip surveys were undertaken in 131 villages where 29,753 people were examined and 492,600 blackflies were analyzed for the presence of Onchocerca volvulus larva using a specific DNA probe. There was a declining trend in infection and transmission levels after the last treatment. In two sites the prevalence of microfilaria and vector infectivity rate were zero 3 to 4 years after the last treatment. In the third site, where infection levels were comparatively high before stopping treatment, there was also a consistent decline in infection and transmission to very low levels 3 to 5 years after stopping treatment. All infection and transmission indicators were below postulated thresholds for elimination.

Conclusion/Significance

The study has established the proof of principle that onchocerciasis elimination with ivermectin treatment is feasible in at least some endemic foci in Africa. The study results have been instrumental for the current evolution from onchocerciasis control to elimination in Africa.

Citation: Traore MO, Sarr MD, Badji A, Bissan Y, Diawara L, et al. (2012) Proof-of-Principle of Onchocerciasis Elimination with Ivermectin Treatment in Endemic Foci in Africa: Final Results of a Study in Mali and Senegal. PLoS Negl Trop Dis 6(9): e1825. doi:10.1371/journal.pntd.0001825