What Is Onchocerciasis?
Onchocerciasis, also commonly known as river blindness, is a Neglected Tropical Disease (NTD) which, in its extreme form, can lead to visual impairment and irreversible blindness. Given that it is the second leading cause of preventable blindness due to infection, we are acting in collaboration with our partners to achieve the elimination of the transmission of river blindness.
What Causes Onchocerciasis?
River blindness is contracted from a parasitic worm called Onchocerca volvulus, transmitted by black flies (Simulium spp.) that live near fast-flowing rivers and streams. Symptoms of onchocerciasis are caused by dead and dying microfilariae, which can cause skin reactions that range from mild to intense itching and can eventually lead to severe dermatitis.
The disease is endemic in 37 countries worldwide, and more than 99% of infected people live in 30 African countries. Currently, around 218 million people live in endemic areas (WHO report 2019-2020). Eliminating the transmission of river blindness worldwide could save the sight of thousands of people each year.
History Of Onchocerciasis
Though onchocerciasis has been in existence for centuries, it was first scientifically observed about 140 years ago. It is thought to have originated in the major river basins of Africa and spread outside the continent via human activity.
Prevention and Treatment Of Onchocerciasis
River blindness can be treated and prevented through repeated mass drug administration (MDA) – the campaigns for which typically last 12-15 years – which is the lifespan of the adult worm. The primary drug for treatment of river blindness is Mectizan (ivermectin), donated by Merck & Co. free of charge for as long as necessary, and in areas where onchocerciasis and lymphatic filariasis are co-endemic, the treatment is ivermectin co-administered with albendazole, which is donated by GSK.
The MDA treatment kills the parasite larvae (microfilariae) in the human body, preventing blindness and skin disease in infected persons, and stopping the transmission of the parasite to others. In some countries, black fly vector control is also used as a complementary approach.
Elimination Of Onchocerciasis
Since 2012, four countries have eliminated river blindness. The global target set by the WHO is to eliminate onchocerciasis as a public health problem by 2030.
Mass drug administration
Ivermectin MDA started in the late 1980s, and great strides in reducing morbidity have been made. In most endemic countries in sub-Saharan Africa, ivermectin is distributed annually.
Detection of parasites
Historically, the procedure of choice for the definitive diagnosis of onchocerciasis has been skin snip microscopy. Biochemical methods such as ELISA are more sensitive and less invasive. Antibody-based rapid diagnostic tests offer a less expensive and more field-friendly approach to diagnosis.
Stopping-MDA surveys use entomological evaluation of black flies and epidemiological assessments of children using serology. If successful MDA is stopped and the endemic area moves in post treatment surveillance for 3-5 years (Phase 2).
Entomological surveillance is then used to confirm the elimination of transmission and progression of the endemic area into post elimination surveillance (Phase 3), until permanent cessation of treatment (Lakwo et al 2020).
To achieve elimination of the transmission a single dose of ivermectin MDA alone might not be sufficient. There is a need for alternative treatment strategies. The antibiotic drug doxycycline which kills the O. volvulus symbiotic bacterium Wolbachia resulting in irreversible elimination of skin microfilaria though direct effects on the endosymbiont is available. Although effective, the duration of the treatment is not suitable for MDA. Attention has been drawn to moxidectin, which clinical trials in phases 2 and 3 have shown superiority of the drug compared to ivermectin. In 2018, Moxidectin has been approved by the US FDA for the treatment of river blindness in people 12 years of age and older.
Challenges faced in eliminating onchocerciasis
- Inadequate health infrastructure
- Logistical issues
- Community fatigue/lack of community engagement
- Issues with data management
- Political will
- Communities no longer perceiving RB as a threat
- Co-endemic with other NTDs
Although most onchocerciasis endemic areas in Africa have a well-established drug distribution system and are moving towards, or have reached, very low levels of transmission following distribution of ivermectin, there are still areas that are very challenging due to:
- Civil unrest
- Co-endemicity of onchocerciasis and loiasis
- Incomplete elimination mapping of all transmission zones
- Technical and financial challenges
- Uncoordinated cross-border elimination efforts