Table 1.

Key lessons learned from onchocerciasis elimination in Africa

1. The proof of principle of onchocerciasis elimination in Africa has been established for vector control and mass treatment with ivermectin.

2. The reproductive lifespan of the adult worm is on average 10 years. Repeated ivermectin treatment reduces adult worm lifespan and/or productivity.

3. Long distance migration of up to 500 km, by infective vectors, can maintain transmission at the point of their arrival despite local control activities. Knowledge of local vector species is therefore important to aid in addressing the phenomenon.

4. Community directed treatment with ivermectin is effective and sustainable.

5. The number of years of mass ivermectin treatment required to achieve elimination is not constant but varies with endemicity level at the onset and treatment coverage. For annual treatment it ranges from 6 to 8 years for hypoendemic areas to over 20 years for holoendemic foci.

6. Evaluation of progress towards elimination involves comparing observed and predicted infection levels after correction for endemicity and reported treatment coverage. It is essential for planning and identifying areas with insufficient progress. The latter is usually due to treatment coverage problems and its timely detection/correction is critical.

7. The skin snip is invasive and increasingly rejected by populations, but it measures active infection which makes it an effective tool for evaluating progress. Serology is less invasive but measures past exposure making it less appropriate.

8. Epidemiological surveys or impact assessment should prioritise high-risk areas and high-risk age groups. Sampling strategies should enable detection of residual pockets of infection.

9. OCP and APOC have established entomological and epidemiological criteria for stopping interventions. These criteria have a clearly defined epidemiological rationale and have been operationally validated at scale. There is no such epidemiological evidence yet for serology.

10. Model predictions and empirical evidence show that infection and transmission do not have to be zero before interventions can be stopped and that low level thresholds exist at which it is safe to stop treatment. The aim of epidemiological evaluations is not to confirm zero prevalence but that the infection level is below the threshold for safely stopping treatment.