Onchocerciasis Part I

Onchocerciasis, also known as river blindness, is a dermic filariasis caused by the nematode Onchocerca volvulus. The disease is found in 30 African countries between latitudes 15°N and 14°S. About 20.9 million people were estimated infected globally (2017) of which 14.6 million had skin disease while 1.15 million had vision loss. Worldwide, onchocerciasis is a very important infectious cause of blindness, being second only to trachoma. Transmitted by the vector, Simulium damnosum, the adult parasite lives up to 14 years in humans, producing millions of microfilariae, which are responsible for the pathology of the disease. The disease presents incessant pruritus, acute and chronic papular onchodermatitis, and eye lesions that often end in blindness. There is evidence of protective immunity at play in these lesions. Onchocerciasis is responsible for 1.23 million (95% UI 0.765–1.82) DALYs (disability-adjusted life years) annually, with troublesome itching accounting for 60% while blindness and visual impairment account for 40% of the attributable DALYs. Individual diagnosis depended on symptomatology and parasitological tests. Parasitological tests together with rapid epidemiological mapping (nodule palpation) used for community diagnosis have produced geographical distribution of onchocerciasis in Africa. Larviciding was used successfully for control in the West African Onchocerciasis Control Programme, while the African Programme for Onchocerciasis Control and Partners have driven the control and now elimination through community-directed treatment with ivermectin in the rest of the endemic African countries. Current efforts geared toward elimination of the disease, necessitate extending operations beyond the previously covered areas with the attendant managerial, financial, and logistic challenges. Some challenges of onchocerciasis control included in the following list have become more pertinent with the change to elimination: (1) the diagnostic tool that needs to be highly specific and sensitive as in evaluations in elimination, low level infection in endemic areas is encountered. This necessitates accurate diagnosis to determine when to stop mass drug administration (MDA) and to identify areas with ongoing low transmission requiring continued MDA; (2) finding a technical and cost-effective approach to eliminating onchocerciasis in co-endemic areas with Loa loa without the occurrence of severe adverse reaction. Other challenges to address include (3) how to minimize noncompliance with the drug treatment; (4) the best approach to obtain sustainability of the drug distribution program; (5) how to sustain community engagement/interest in MDA; (6) discovering an acceptable macrofilaricide that can either kill or sterilize the adult; (7) how to optimize treatment regime of possible antibiotic that targets Wolbachia endobacteria the elimination of which will incapacitate the adult worm; and (8) how to discover early, any resistance to the current drug. All these require research, which was always central to the two erstwhile control programs.