Onchocerca

Hendy, Adam, Krit, Meryam, Pfarr, Kenneth, Laemmer, Christine, Witte, Jacobus De, Nwane, Philippe, Kamgno, Joseph, Nana-Djeunga, Hugues C., Boussinesq, Michel, Dujardin, Jean-Claude, Post, Rory, Colebunders, Robert, O’Neill, Sarah, Enyong, Peter & Njamnshi, Alfred K., 2021, ONCHOCERCA VOLVULUS transmission in the Mbam valley of Cameroon following 16 years of annual community-directed treatment with ivermectin, and the description of a new cytotype of SIMULIUM SQUAMOSUM, Parasites & Vectors (563) 14 (1), pp. 1-14 : 9

Onchocerca species transmission intensity as assessed by dissection

Parasites that were morphologically similar to O. volvulus were mainly transmitted between January and May, overlapping the dry and rainy seasons during this period. The ATP was higher and peaks in transmission occurred slightly later at Bayomen ( ATP 4488 ) than at Nyamongo I (2360) ( Fig. 6b ; Additional file 1: Table S 6). The mean number of L3H per infective fly was higher at Bayomen (6.4) than Nyamongo I (2.4), and the highest estimated MTP (2406) at Bayomen was calculated based on just two infective flies carrying 17 L3H parasites. When data were combined for the two riverside sites, there was no effect of rainy season on the proportion of flies carrying only L1 and L2 stage parasites (P = 0.528), suggesting that they were present throughout the year ( Fig. 6a ). However, the proportion of flies carrying L3H parasites was higher in the March – June rainy season (P = 0.043), corresponding with higher parity rates and suggesting that parasites were developing to transmissible forms during this period ( Fig. 6a ). At Egona II, the ATP (102) was substantially lower than at the riverside sites ( Fig. 6b ; Additional file 1: Table S 6). Infective L 3H parasites were only found at Egona II in two flies collected in April 2017, at the beginning of the rainy season and shortly after biting rates had peaked (Additional file 1: Table S 3). No parasites of any stage were found in the 489 flies dissected at Ondouano during the study (Additional file 1: Table S 4). When considering all L 3 larvae, regardless of their location in the blackfly, the ATP at Bayomen increased to 5479, but all other sites remained unchanged.

Figures

Fig. 6 Seasonal parasite transmission along the lower Mbam river showing a combined parity and infection rates for flies dissected at Bayomen and Nyamongo I riverside sites (L1–L2= percentage of flies infected with developing parasite stages only, L3H =percentage of flies containing L3 stages in the head), and b monthly transmission potentials at Bayomen, Nyamongo I, and Egona II estimated based on dissection data only. Ondouano not shown since no larvae were found in dissected flies