A Major Public Health Milestone on the Horizon: 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 female worms live in the human body for around 15 years and release thousands of microfilariae daily. 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, the National Onchocerciasis Control Program was established in Sierra Leone. Vector control began by spraying insecticide from helicopters over blackfly breeding sites along the banks of fast-flowing rivers. This was stopped due to the civil war in 1995. Baseline microfilariae studies after the war (2002-2004) confirmed onchocerciasis was endemic in all districts of Sierra Leone except the Western Area. In 1987 the Mectizan® Donation Program was announced, committed to making Ivermectin (Mectizan) freely available for Onchocerciasis control programs “for as long as it was needed”. 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, Community-Directed Treatment with Ivermectin must reach 80 percent or more of the at-risk population annually for at least 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 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 Community-Directed Treatment with Ivermectin 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 migrations 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 USAID-funded End in Africa program. Helen Keller International has provided technical support to the program, working hand in hand with the Sierra Leone Ministry of Health.

An impact assessment conducted by the World Health Organization in 2010 found microfilariae prevalence had dropped from 53 percent at baseline to 21 percent. The battle to eliminate onchocerciasis 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, difficulty accessing  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 2016, the Sierra Leone Government and partners assembled an expert committee to plan for the final stages of onchocerciasis elimination. This year, the national program and its partners seized the opportunity to assess the status of onchocerciasis in 8 of the country’s 14 districts, using a rapid finger prick blood test to detect the Onchocerca volvulus antigen. Preliminary findings by the Sierra Leone Ministry of Health and Sanitation showed that the prevalence in randomly selected school children aged 5-10 years old was less than 3 percent in all districts. Moreover, no new cases of blindness due to Onchocerciasis have been reported by national eye care teams since 2010. It is anticipated that Community-Directed Treatment with Ivermectin will cease to be necessary soon after 2020 and World Health Organization accreditation of onchocerciasis elimination could be awarded following 3 to 5 years of successful surveillance. 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 verge of this 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.