Fifteen years of annual mass treatment of onchocerciasis with ivermectin have not interrupted transmission in the west region of cameroon

Moses N Katabarwa, Albert Eyamba, Philippe Nwane, Peter Enyong, Joseph Kamgno, Thomas Kueté, Souleymanou Yaya, Rosalie Aboutou, Léonard Mukenge, Claude Kafando, Coulibaly Siaka, Salifou Mkpouwoueiko, Demanga Ngangue, Benjamin Didier Biholong, Gervais Ondobo Andze, Moses N Katabarwa, Albert Eyamba, Philippe Nwane, Peter Enyong, Joseph Kamgno, Thomas Kueté, Souleymanou Yaya, Rosalie Aboutou, Léonard Mukenge, Claude Kafando, Coulibaly Siaka, Salifou Mkpouwoueiko, Demanga Ngangue, Benjamin Didier Biholong, Gervais Ondobo Andze

Abstract

We followed up the 1996 baseline parasitological and entomological studies on onchocerciasis transmission in eleven health districts in West Region, Cameroon. Annual mass ivermectin treatment had been provided for 15 years. Follow-up assessments which took place in 2005, 2006, and 2011 consisted of skin snips for microfilariae (mf) and palpation examinations for nodules. Follow-up Simulium vector dissections for larval infection rates were done from 2011 to 2012. mf prevalence in adults dropped from 68.7% to 11.4%, and nodule prevalence dropped from 65.9% to 12.1%. The decrease of mf prevalence in children from 29.2% to 8.9% was evidence that transmission was still continuing. mf rates in the follow-up assessments among adults and in children levelled out after a sharp reduction from baseline levels. Only three health districts out of 11 were close to interruption of transmission. Evidence of continuing transmission was also observed in two out of three fly collection sites that had infective rates of 0.19% and 0.18% and ATP of 70 (Foumbot) and 300 (Massangam), respectively. Therefore, halting of annual mass treatment with ivermectin cannot be done after 15 years as it might escalate the risk of transmission recrudescence.

Figures

Figure 1
Figure 1
Map of West Region of Cameroon showing the study areas.
Figure 2
Figure 2
Comparison of mf rates among adults and children at baseline, 1996, with followup surveys in 2005, 2006, and 2011 in West Region of Cameroon.
Figure 3
Figure 3
Monthly seasonal biting of Simulium flies at 3 fly catching sites in West Region.

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