Onchocerciasis elimination feasible with ivermectin treatment

Jul 21 2009

The first evidence that onchocerciasis elimination is feasible with ivermectin treatment was published in the open-access journal PLoS Neglected Tropical Diseases. Onchocerciasis is also called river blindness because the blackfly which transmits the disease breeds in rivers; it often blinds people, as well as causing debilitating skin disease. Over 37 million people are infected, often living in poor, rural African communities.

"This evidence is an historic milestone -- it has far-reaching implications for the fight against this disease. Prior to this study we did not know if we would ever be able to stop treatment," says Uche Amazigo, the Director of the African Programme for Onchocerciasis Control (APOC). APOC is the organization charged with implementing control of the disease across Africa.

The multi-country study showed that treatment with ivermectin stopped further infections and transmission in 3 specific areas in Africa where the disease has existed continuously (an endemic area).

Annual treatments to prevent resurgence

Ivermectin kills the larvae but not the adult worms of Onchocerca volvulus, the parasite that causes the disease, so annual or biannual treatments are required to prevent resurgence. Merck & Co., the company that discovered and manufactures the drug, agreed in 1987 to donate the drug free of charge to countries where onchocerciasis is endemic. This has resulted in annual treatments to all eligible community members - over 60 million people were treated in 26 African countries in 2008. But although this large-scale treatment has enabled the control of onchocerciasis in Africa, it has not been clear whether it could also be used to eliminate infection and transmission to the extent that treatment with ivermectin could be safely stopped. Many scientists have doubted whether onchocerciasis elimination with ivermectin is feasible in Africa, where more than 99% of cases are found.

This new study in three areas in Mali and Senegal where onchocerciasis was endemic has now provided the first evidence of the feasibility of onchocerciasis elimination with ivermectin in some endemic areas in Africa. Previously, it was thought that elimination of onchocerciasis was only possible in the limited, isolated areas in the Americas where the disease is endemic.

However, the studies showed that after 15 to 17 years of six-monthly or annual treatments, only a few infections remained in the human population. Transmission levels were below predicted thresholds for elimination, so treatment was subsequently stopped in test areas and follow-up evaluations after 1.5 to 2 years showed that no further infections or transmission occurred.

Further studies needed

Although further studies are needed to determine to what extent these findings can be extrapolated to other areas in Africa, the principle of onchocerciasis elimination with ivermectin treatment has been established. Dr Robert Ridley, Director of TDR, the Special Programme for Research and Training in Tropical Diseases (that coordinated the study), said, "This is an excellent example of how research like this can not only provide important answers to major health questions, but with this type of partnership, can also help develop research capacity in low-income countries."

As a result of the study, the board of APOC has already adopted a new objective for the programme to determine where and when treatment can be safely stopped in the 16 African countries where APOC is supporting mass ivermectin treatment programmes.

The studies were undertaken by research teams from the ministries of health of Mali and Senegal, in collaboration with the WHO Multi-Disease Surveillance Centre in Burkina Faso. Main funding for the study was provided by the Bill & Melinda Gates Foundation. The study was coordinated by TDR, a co-sponsored programme of UNICEF, UNDP, the World Bank and WHO.

TDR conducted much of the earlier research to prove that this drug was safe and effective. The partnership with Merck & Co. the MECTIZAN Donation Program, WHO, APOC and the national control programmes is considered an early model of the numerous public-private partnerships that have sprung up in the last decade.