Neglected Tropical Disease Highlight: Onchocerciasis

By: Daisy Liu

The impact of the COVID-19 pandemic is far-reaching and felt all over the world. This includes elimination programs in lower-middle-income countries, stalling progress and, at some point, even halting activities altogether. The Neglected Tropical Disease Highlight attempts to bring attention to these instances and proposed solutions.


Onchocerciasis is a condition that primarily affects low-income populations in Africa and Latin America. Alternatively known as “river blindness”, this disease is the second greatest cause of blindness and is associated with reduced life expectancy, decreased productivity, as well as heavy stigma due to its highly visible symptoms. As a topic for global health scholarship, onchocerciasis provides an interesting case study of a successful primary health care (PHC) intervention as well as a neglected tropical disease.

Epidemiology and pathophysiology

Onchocerciasis is caused by Onchocerca volvulus (O. volvulus), a parasitic filarial nematode transmitted by the bites of blood-sucking blackflies (genus Simulium) that breed in fast-flowing water bodies. To date, scientists have identified two major variants of the disease: (1) ocular onchocerciasis and (2) dermal onchocerciasis. Features of the ocular form of this disease include lesions leading to decreased vision, corneal blindness, and visible changes to the eye due to invasion and subsequent death of microfilaria. Conversely, the dermal form of onchocerciasis causes symptoms such as persistent itching and visible changes in skin colour and/or texture (i.e., lichenification, and “leopard skin”). Death of the microfilariae causes destructive autoimmune reactions as well as inflammation, potentially causing the other, visible symptoms. Researchers suspect connections between onchocerciasis and neurological conditions such as Nakalanga syndrome and Nodding syndrome, and skin snip studies have found that childhood infection possesses strong predictive value for developing onchocerciasis-related epilepsy (ORE) in later adulthood. As of 2019, onchocerciasis is most prevalent in Africa while also being in many Latin American countries. Interestingly, the distribution of onchocerciasis outside of Africa reflects the destinations of slaves. In many foci, the disease then interacts with other legacies of colonialism such as poor national health infrastructure and public health messaging systems to generate a variety of costs for patients.

Aside from its impacts on physical health, onchocerciasis has been demonstrated to have a large array of other negative effects. Investigations of onchocerciasis in endemic villages in 1970 showed that the disease took heavy psychological, social, and economic tolls from its patients. Further research reveals gendered dimensions of the disease, and that the unaffected and affected populations of both genders demonstrate markedly different attitudes towards infection with the disease. However, due to the subsistence economies of many onchocerciasis foci, enumerating the impact of the disease on productivity can be extremely difficult.

COVID-19 and Onchocerciasis

In April 2020, WHO recommended the suspension of all epidemiological surveys and mass drug administration (MDA) for NTDs as part of the effort against COVID-19. While this has since been lifted to a point where activities may resume so as they are conducted “safely”, concerning patterns still emerge. In his 2021 article, Jonathan I.D. Hamley et al. describe the impact of lockdowns on the mass deliveries of ivermectin to endemic countries in Africa. Using various models, the research team found that, without mitigation strategies and substantial changes to MDA plans, the original goal of onchocerciasis elimination by 2030 is impossible. Children under 10 years of age are among the most affected (as measured by microfilarial load) due to late treatment initiation while older age groups also suffer increased infection prevalence and intensity.


As an NTD that nonetheless receives large amounts of international attention, the history of onchocerciasis is perhaps unique in its diversity and its extremely successful treatment program. In many ways, APOC experiences and designs serve as powerful examples of the power of well-funded PHC programs. However, investment and resource availability is of utmost importance in ensuring proper execution and treatment coverage. Indeed, had a person with fewer financial resources than the former-World Bank president taken on the onchocerciasis program, even if they were also the head of an international organisation, disease outcomes may have been very different. Now, it is this crucial aspect of onchocerciasis programs that are being threatened along with the treatment infrastructure that had been carefully developed over decades. Unfortunately, the intertwining of ecological, political, and sociocultural factors destroy the possibility of a developmental or biomedical magic bullet and muddy absolutist understandings of disease management—this much is recognised by researchers around the world. Proposed approaches include that of “hybridising” COVID-19 and NTD programmes in order to promote behaviour that mitigates the spread of many diseases at once. This capitalises on the existence of common pathways of transmission (e.g., poor hygiene) in order to strengthen health systems and facilitate integration. In the face of an uncertain future regarding both the COVID-19 pandemic and the resumption of MDA, this approach best makes use of the existing resources to their maximum effect.


Alonso LM, Murdoch ME, Jofre-Bonet M. 2009. Psycho-social and economic evaluation of onchocerciasis: a literature review. Social Medicine. 4(1): 8-31.

Amazigo U, Noma M, Bump J, Benton B, Liese B, Yaméogo, Zouré H, Seketeli A. 2006. Onchocerciasis In: editors. Disease and Mortality in Sub-Saharan Africa. 2nd edition. Washington DC: The World Bank. p. 215-223.

Babalola OE. 2011. Ocular onchocerciasis: current management and future prospects. Clinical Ophthalmology. 5: 1479-1491.

Chesnais CB, Nana-Djeunga HC, Njamnshi AK, Lenou-Nanga CG, Boullé C, Bissek ACZK, Kamgno J, Colebunders R, Boussinesq M. 2018. The temporal relationship between onchocerciasis and epilepsy: a population-based cohort study. Lancet Infectious Diseases. 18(11): 1278-1286.

Crump A, Morel CM, Omel S. 2012. The onchocerciasis chronicle: from the beginning to the end?. Trends in Parasitology. 28(7): 280-288.

Föger K, Gora-Stahlberg G, Sejvar J, Ovuga E, Jilek-Aall L, Schmutzhard E, Kaiser C, Winkler AS. 2017. Nakalanga syndrome: Clinical characteristics, potential causes, and its relationship with recently described nodding syndrome. PLoS Neglected Tropical Diseases. 11(2): 1-15.

Gebrezgabiher G, Mekonnen Z, Yewhalaw D, Hailu A. 2019. Reaching the last mile: main challenges relating to and recommendations to accelerate onchocerciasis elimination in Africa. Infectious Diseases of Poverty. 8(60): 1-12.

Hamley JID, Blok DJ, Walker M, Milton P, Hopkins AD, Hamill JC, Downs P, de Vlas SJ, Stolk WA, Basáñez MG. 2021. What does the COVID-19 pandemic mean for the next decade of onchocerciasis control and elimination?. Transactions of The Royal Society of Tropical Medicine and Hygiene. 115(3): 269–280.

Hill E, Hall J, Letourneau ID, Donkers K, Shirude S, Pigott DM, Hay SI, Cromwell EA. 2019. A database of geopositioned onchocerciasis prevalence data. Scientific Data. 6(67): 1-6.

Molyneux D, Bush S, Bannerman R, Downs P, Shu’aibu J, Boko-Collins P, Radvan I, Wolgemuth L, Boyton C. 2021. Neglected tropical diseases activities in Africa in the COVID-19 era: the need for a “hybrid” approach in COVID-endemic times. Infectious Diseases of Poverty. 10(1).

Homieda M, Braide E, Elhassan E, Amazigo UV, Liese B, Benton B, Noma M, Etya’alé, Dadzie KY, Kale OO, Sékétéli A. 2001. APOC's strategy of community-directed treatment with ivermectin (CDTI) and its potential for providing additional health services to the poorest populations. African Programme for Onchocerciasis Control. Annals of Tropical Medicine and Parasitology. 96(sup1): S93-S104.

Norice-Tra CT, Ribeiro J, Bennuru S, Fay MP, Tyagi R, Mitreva M, Butman TB. 2017. Insights Into Onchocerca volvulus Population Biology Through Multilocus Immunophenotyping. Journal of Infectious Diseases. 216(6): 736-743.

Romo ML, Nash D. 2018. Onchocerciasis and epilepsy: a causal relationship?. Lancet Infectious Diseases. 18(11): 1172-1174.

Taylor MJ, Hoerauf A, Bockarie M. 2010. Lymphatic filariasis and onchocerciasis. Lancet. 376(9747): 1175-1185.

Vlassoff C, Weiss M, Ovuga EBL, Eneanya C, Nwel PT, Babalola SS, Awedoba AK, Theophilus B, Cofie P, Shetabi P. 2000. Gender and the stigma of onchocercal skin disease in Africa. Social Science & Medicine. 50(10): 1353-1368.

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