Onchocerciasis and lymphatic filariasis research

Onchocerciasis (River blindness)

Onchocerciasis is an eye and skin disease caused by the parasite Onchocerca volvulus. The symptoms, including itching, changes in the skin, visual impairment and even blindness, are caused by the body’s inflammatory response to dying O. volvulus microfilariae. The parasite is transmitted by blackflies of the genus Simulium. They breed in fast flowing rivers which has contributed to the name ‘river blindness’. More than 99% of affected people live in sub-Saharan Africa.

Lymphatic filariasis (Elephantiasis)

Lymphatic filariasis is caused by three different species of roundworms: Brugia malayi, Brugia timori and by Wuchereria bancrofti, which accounts for around 90% of infections.  The adult parasites (macrofilariae) live in the lymphatic system. The inflammation this causes damages the lymphatic system which ultimately results in lymphoedema and hydrocele.  Lymphoedema affects primarily the lower limbs and its advanced form has contributed to the name ‘elephantiasis’.  

Background

TDR has a long history of research to support the control of onchocerciasis as the ‘research arm’ of the Onchocerciasis Control Programme in West Africa (OCP, 1974–2002) and the African Programme for Onchocerciasis Control (APOC, 1995-2015). TDR-managed studies demonstrated, for example, the safety and effectiveness of community-directed treatment with ivermectin (CDTI, the current control and elimination strategy) and that long-term CDTI can not only control onchocerciasis as a public health problem but may also allow to eliminate parasite transmission.

More recently, TDR funded and managed the clinical studies in Africa which provided the evidence that moxidectin reduces skin microfilariae levels in more people, to a larger extent and for longer than ivermectin.  These data supported regulatory approval of moxidectin for treatment of O. volvulus infected people ≥12 years by the Food and Drug Administration of the United States of America.  

Currently, TDR supports:

• Further research on moxidectin, a new drug for onchocerciasis and potentially other NTDs. TDR provides scientific and technical advice on additional studies required to support decisions on incorporating moxidectin into WHO guidelines and country policies for onchocerciasis elimination, to evaluate the efficacy of moxidectin for other diseases of poverty and to develop a paediatric formulation.
• Research for tools to estimate and minimize the risk of resurgence after mass drug administration for onchocerciasis and lymphatic filariasis has been stopped, monitor decline of the reproductively active O. volvulus population and monitor O. volvulus response to ivermectin.
        

For more information, contact:
Dr Annette Kuesel