Towards a Major Public Health Milestone: Sierra Leone's Progress towards Eliminating River Blindness

Photo By: Henry Allieu

River blindness (onchocerciasis) has been known to humankind since “biblical times”. It was second only to cataract as a cause of blindness in Sierra Leone until recently – It used to be so common in some highly-affected riverside villages that people accepted the inevitability of visual impairment from their mid-30s.

The parasite that causes onchocerciasis, Onchocerca volvulus, was first identified in 1874 and its transmission as larvae by blackflies was first documented in 1926 in Sierra Leone. The mature worms live in the human body for around 15 years and the females release thousands of microfilariae daily that typically live in the skin for up to two years. The body’s inflammatory response leads to a variety of skin and eye conditions, including severe itching, nodules, and visual impairment, ultimately leading to permanent blindness. These physical manifestations devastate the quality of life of those living in endemic communities and severely reduce their economic earning capacity as well as the educational opportunities of the younger generation caring for their blind elders.

In 1988, Sierra Leone’s National Onchocerciasis Control Program was established. Vector control began by spraying insecticide from helicopters over blackfly breeding sites along the banks of fast-flowing rivers. This was suspended due to Sierra Leone’s civil war in 1995. Baseline microfilariae studies spanning the period 1988 to 2005 confirmed onchocerciasis was endemic in all districts of Sierra Leone except the Western Area, according to a Sierra Leone Ministry of Health and Sanitation report.

In 1987 the Mectizan® Donation Program was announced, committed to making ivermectin (Mectizan) freely available for onchocerciasis control programs for as long as necessary. This was first major pharmaceutical commitment of its kind and enabled the expansion of community-directed treatment with ivermectin (CDTI) by the African Program for Onchocerciasis Control. CDTI was adopted in Sierra Leone in 2003 in moderately and highly endemic communities. Ivermectin kills the microfilariae produced by female worms. To be effective, CDTI must reach 80 percent or more of the at-risk population annually for about 15 years to break the cycle of transmission. This approach targeted everyone over the age of five years except pregnant and post-partum women, the sick and the very elderly.

Information, education and communication materials were introduced, and community meetings held with civil, traditional and religious leaders. All front-line health workers, as well as local volunteers called community drug distributors (CDDs), were trained. Effective coverage in Sierra Leone was achieved in 2007 and has been maintained ever since, targeting around 3 million people at risk annually. In 2007, the national program also began integrated lymphatic filariasis (“elephantiasis”) control by adding albendazole to CDTI nationwide.

Social mobilization approaches were diversified in 2010 to include “frequently asked questions” and a wider range of avenues of communication, such as interactive radio broadcasts and social media.

Monitoring and evidence-based programming have been fundamental throughout. In 2010, in- and end-process independent monitoring was introduced to validate coverage levels, as urbanization and internal migration had made population projections unreliable. This also enabled a better understanding of reasons for people not receiving ivermectin or albendazole.

International donors have provided essential financial assistance -- most notable among these has been the United States Agency for International Development (USAID).  USAID support began with their Neglected Tropical Disease Control Program and has continued with the End in Africa Project. Helen Keller International (HKI) has provided technical support to the program, working hand in hand with the Sierra Leone Ministry of Health and Sanitation. An impact assessment at sentinel sites supported by the World Health Organization in 2010 found microfilariae prevalence had dropped by 60 percent from baseline levels.

The battle to eliminate onchocerciasis in Sierra Leone has been interrupted twice by national emergencies, first during the civil war (1991-2002) and then during the Ebola crisis of 2014-2015.  Progress was also disrupted by a major cholera outbreak in 2012. Even in the best of times, there are numerous challenges, including maintaining volunteers’ motivation, difficult access to remote communities (particularly during the long, intense rainy season), community awareness deficits, vector control issues, morbidity management gaps, cross-border migration with Guinea and Liberia and disease surveillance challenges. In spite of these challenges and interruptions, the national program, with assistance from partners, has gotten program activities back on track as soon as it became feasible each time.

In 2016, the Sierra Leone Government and partners assembled an advisory committee to assist in planning for the final stages of onchocerciasis elimination. This year, the national program and its partners seized the opportunity to test a rapid-finger-prick blood test to detect the Onchocerca volvulus antigen in children in 12 of the country’s 14 districts using the lymphatic filariasis transmission assessment survey methodology. Preliminary findings of this survey suggest that the transmission of onchocerciasis continues in some areas, but the overall prevalence in randomly-selected school children aged 5-10 years old was at a low level. Moreover, no new cases of blindness due to onchocerciasis have been reported by national eye care teams since 2010. Nevertheless, CDTI is likely to continue for now. The national program is planning to conduct epidemiological and entomological assessments in the next couple of years, and key public health actors hope that Sierra Leone will be able to achieve the goal of onchocerciasis elimination by 2025.

In spite of myriad challenges, Sierra Leone’s track record on controlling and moving toward elimination of onchocerciasis is a success story. Nearly a century after the disease’s transmission was first documented, Sierra Leone is on the right track for a remarkable achievement. This should be applauded as a monumental public health intervention that has already improved lives and made a significant contribution to the nation’s sustainable development.

This blog post was co-authored by John Uniack Davis, Ph.D., West Africa Regional Director for Helen Keller International, and Mary Hodges, M.B.B.S., M.R.C.P., D.Sc., Country Director of HKI in Sierra Leone. The authors thank Dr. Yaobi Zhang for his useful comments.