Annual biting rates.

<p>Annual biting rates of <i>Onchocerca</i> spp. from two onchocerciasis foci in North Cameroon. Each data point starts at the beginning of the rainy season (April) till the end of the dry season (March of the following year). Years with no data are left blank. <b>A</b> Soramboum, Vina du Nord. Epidemiological data prior to 1998 was published before and modified to fit this graph. Data from 1976 was taken from Touboro, 30 km further downstream. <b>B</b> Galim, Vina du Sud. Epidemiological data prior to 1997 was published before and modified to fit this graph.</p

Entomologic parameters and proportion of filarial stages from <i>Simulium damnosum s</i>.<i>l</i>. at two different sites in Northern Cameroon.

<p>Entomologic parameters and proportion of filarial stages from <i>Simulium damnosum s</i>.<i>l</i>. at two different sites in Northern Cameroon.</p

L3 species proportion.

<p>Species composition of infective third-stage larvae from <i>S</i>. <i>damnosum s</i>.<i>l</i>. at two foci in North Cameroon. White: <i>O</i>. <i>volvulus</i>; light grey: <i>O</i>. <i>ochengi</i> 'Siisa' type; medium grey: <i>O</i>. <i>ochengi</i>; dark grey: <i>O</i>. <i>ramachandrini</i>. <b>A-B</b> Soramboum, Vina du Nord. <b>C-D</b> Galim, Vina du Sud. Left side (A, C): morphological identification. Right side (B, D): PCR-based identification.</p

L3 body lengths.

<p>Violin plot of the L3 body lengths of identified <i>Onchocerca</i> spp. in <i>S</i>. <i>damnosum s</i>.<i>l</i>. from North Cameroon. Species identification is based on morphological (light grey) and molecular-genetic (dark grey) characteristics. Two genotypes of <i>O</i>. <i>ochengi</i>, <i>O</i>. <i>ochengi s</i>. <i>str</i>. and <i>O</i>. <i>ochengi</i> 'Siisa', are shown based on their mitochondrial clades. ***<i>P</i> < 0.001; **0.01 > <i>P</i> > 0.001; *<i>P</i> < 0.05.</p

Annual transmission potentials.

<p>Annual transmission potentials of <i>Onchocerca</i> spp. from two onchocerciasis foci in North Cameroon. Data is given at the beginning of the rainy season (April) till the end of the dry season (March of the following year). Dark grey: <i>O</i>. <i>ramachandrini</i>; light grey: <i>O</i>. <i>ochengi</i>; white: <i>O</i>. <i>volvulus</i>. Insufficient fly dissection data from 1986, 1989–1992 in Soramboum, and from 1985–1987, 1990 and 1997 in Galim have been extrapolated. In 1976 (color transition of white, light grey to dark grey) no species discrimination was done. ATP with available MTP data ≥ 80% have borders in bold; those with data 80% > x ≥ 30% have normal borders, and those with data < 30% have borders with a dotted line. The dotted line marks the beginning of ivermectin mass treatments. The asterisk indicates the introduction of PCR-based methods for species discrimination in the vector. Prior to 1990, the L3 species was determined according to the following body length criteria: <i>O</i>. <i>volvulus</i> ≤ 750 μm; 750 μm < <i>O</i>. <i>ochengi</i> < 900 μm; <i>O</i>. <i>ramachandrini</i> ≥ 900 μm. <b>A</b> Soramboum, Vina du Nord. Epidemiological data prior to 1998 was published before and modified to fit this graph. Data from 1976 was taken from Touboro, 30 km further downstream. <b>B</b> Galim, Vina du Sud. Epidemiological data prior to 1997 was published before and modified to fit this graph.</p

Study area.

<p>Overview map of the study sites (yellow circles) from two river basins in Northern Cameroon. The village Galim at the Vina du Sud river near Ngaoundéré is on the Adamawa highland plateau, an area above 900 m altitude (dark grey area) with intense cattle husbandry. The village Soramboum at the Vina du Nord river towards Touboro is located in the Sudan savannah (light grey area), a region not often frequented by cattle herds and with high wildlife density. Diagrams of hydrological data showing the mean monthly water discharge from three river basins is taken from Olivry [<a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0004392#pntd.0004392.ref026" target="_blank">26</a>]. CAR: Central African Republic.</p

Ongoing Transmission of <i>Onchocerca volvulus</i> after 25 Years of Annual Ivermectin Mass Treatments in the Vina du Nord River Valley, in North Cameroon

<div><p>Background</p><p>Recent reports of transmission interruption of <i>Onchocerca volvulus</i>, the causing agent of river blindness, in former endemic foci in the Americas, and more recently in West and East Africa, raise the question whether elimination of this debilitating disease is underway after long-term treatment of the population at risk with ivermectin. The situation in Central Africa has not yet been clearly assessed.</p><p>Methods and findings</p><p>Entomologic data from two former endemic river basins in North Cameroon were generated over a period of 43 and 48 months to follow-up transmission levels in areas under prolonged ivermectin control. Moreover, epidemiologic parameters of animal-borne <i>Onchocerca</i> spp. transmitted by the same local black fly vectors of the <i>Simulium damnosum</i> complex were recorded and their impact on <i>O</i>. <i>volvulus</i> transmission success evaluated. With mitochondrial DNA markers we unambiguously confirmed the presence of infective <i>O</i>. <i>volvulus</i> larvae in vectors from the Sudan savannah region (mean Annual Transmission Potential 2009–2012: 98, range 47–221), but not from the Adamawa highland region. Transmission rates of <i>O</i>. <i>ochengi</i>, a parasite of Zebu cattle, were high in both foci.</p><p>Conclusions/significance</p><p>The high cattle livestock density in conjunction with the high transmission rates of the bovine filaria <i>O</i>. <i>ochengi</i> prevents the transmission of <i>O</i>. <i>volvulus</i> on the Adamawa plateau, whereas transmission in a former hyperendemic focus was markedly reduced, but not completely interrupted after 25 years of ivermectin control. This study may be helpful to gauge the impact of the presence of animal-filariae for <i>O</i>. <i>volvulus</i> transmission in terms of the growing human and livestock populations in sub-Saharan countries.</p></div