River blindness: a success story under threat?

Abstract

The success of the Onchocerciasis Control Programme is undeniable and exemplary, say the authors, but it is too early to claim victory against river blindness.

Figure 1. Life Cycle of O. volvulus

Mean dimensions of parasite stages are: Adult females, 35–70 cm × 400 µm; adult males, 2–4 cm × 150–200 µm; microfilariae, 250–360 × 5–9 µm; L1 larvae, 200 µm × 12 µm (front) and 20 µm (rear); L3, 440–700 × 20 µm. L1 larvae molt into L2, pre-infective larvae, and L2 into L3, infective larvae [5]. (Illustration: Giovanni Maki, derived from a CDC image at http://www.dpd.cdc.gov/dpdx/HTML/Filariasis.htm)

Figure 2. Distribution of Onchocerciasis Showing Current Status of Global Onchocerciasis Control

Red areas represent areas receiving ivermectin treatment. Yellow areas represent areas requiring further epidemiological surveys. The green area is the area covered by the Onchocerciasis Control Programme in West Africa. Pink zones indicate the special intervention zones, i.e., previous OCP areas receiving ivermectin and some vector control. Map redrawn from [53,75,76]

Figure 3. The Incidence of Blindness and Excess Mortality Rate, by Sex, Plotted against O. volvulus Microfilarial Load

Arithmetic mean of microfilarial counts from two skin snips, taken from the right and left ileac crests, using a 2-millimeter Holth corneoscleral punch. (A) Blindness; (B) excess mortality rate. Error bars denote 95 percent confidence intervals [10,22].