Onchocerciasis

Introduction

Onchocerciasis (also known as river blindness) is a vector-borne disease that is transmitted from person to person via the bites of infected blackflies. The disease is caused by the parasitic filarial worm Onchocerca volvulus.

The blackflies introduce immature larval forms of the parasite into the human recipient; these larvae then mature into adult worms, mate and in turn release hundreds of microfilariae a day; these move through the body and cause a number of symptoms, including intense itching and skin rashes, swelling and ultimately severe dermatitis, impaired vision and ultimately blindness.

TDR related research

TDR has a long history of research to support the control of this disease, dating back to the partnership with the Onchocerciasis Control Programme in West Africa (1974-2002) that eliminated the mosquito that transmitted the disease in West Africa. From being the 'research arm' of the Onchocerciasis Control Programme (OCP) in West Africa, TDR moved to being the research arm of the African Progamme for Onchocerciasis Control (APOC, 1995-2015).

Research on how to curb disease transmission in broad savanna regions of West Africa led to the breakthrough innovation of incorporating the Bti bacterium to control insect larvae, including that of the blackfly, in 1982.

TDR also contributed to the design of study protocols and dosage for the drug ivermectin, and connected the pharmaceutical owner, Merck, with the OCP networks. In 1986, with the drug about to be registered, CEO of Merck Dr Roy Vagelos made the momentous decision to donate the drug to whoever needed it, as long as it was needed. TDR and partners set up large-scale community trials under field conditions to move the drug from individual treatment in hospitals to mass drug administration, strengthening the value of ivermectin in the onchocerciasis control strategy.

TDR research in collaboration with the African Programme for Onchocerciasis Control (APOC) has resulted in a new strategy for mass drug administration, community-directed treatment with ivermectin (CDTI), which achieved higher treatment coverage (% of the population taking the drug) than the health system directed ivermectin distribution .

In 2015, more than 110 million people in Africa received ivermectin through CDTI.

More recently, TDR is supporting:

  • The evaluation of another compound, moxidectin, for its potential to accelerate elimination of onchocerciasis and expand the areas where elimination of transmission in Africa is feasible;
  • The identification of genetic markers of the parasite’s response to ivermectin and of O. volvulus transmission zones;
  • The evaluation of the variability of response of O. volvulus and other helminths controlled by preventive chemotherapy to the drugs used to control them;
  • The development of parasite transmission models which can take into account genetically determined variability drug response and allow to model the exchange of parasites between areas with different levels of endemicity or different parasite characteristics (e.g. resistant parasites).

Related links

For more information, please contact Dr Annette Kuesel

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All TDR publications on onchocerciasis