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The Path to the Elimination of Onchocerciasis in the Americas

Onchocerciasis, or river blindness, is a Neglected Tropical Disease (NTD) caused by a parasitic worm (Onchocerca volvulus), transmitted through the bite of the blackfly. The disease is present in many parts of Africa and six countries in the Americas (Brazil, Colombia, Ecuador, Guatemala, Mexico, and Venezuela). In 1991, the ministers of health in the six countries affected by onchocerciasis adopted a resolution to eliminate the disease as a public health problem and to reduce blindness caused by onchocerciasis. At that time, 500,000 persons in the Americas were at risk of blindness.

Initially, the plan to reduce blindness called for treatment one time per year with ivermectin (Mectizan; donated by Merck & Co. Inc). In 1992, the Onchocerciasis Elimination Program for the Americas (OEPA) was established and number of persons treated began to rise rapidly. While once per year treatments were effective in preventing blindness, stopping transmission proceeded slowly. In 1995, the decision was made to initiate treatment two times per year. This proved to be a crucial turning point, as twice yearly treatments led to more rapid progress toward stopping transmission (referred to as interruption of transmission by scientists). Because of the program’s success combating blindness and interrupting transmission, the program goal shifted from reduction of blindness to elimination of disease (noted in the most recent PAHO resolution CD48.R12). Treating as many persons as possible through mass drug administration has led to many successes, including the elimination of blindness caused by onchocerciasis in all 13 areas the disease was present, interruption of transmission in eight of the 13 areas, and suspected interruption in two additional areas.

This map shows the areas where there is still Onchocerciasis transmission in the Americas. It highlights 3 areas in Mexico near the Guatemala border (one of suppressed transmission on the Guatemala border, on of eliminated transmission halfway between the Gulf of Mexico and the Pacific, and one of interrupted transmission further east that the other two), 4 areas in Guatemala (one of interrupted transmission on the Mexican border, one of suppressed transmission closer to Mexico and two of eliminated transmission closer to El Salvador, 3 areas in Venezuela (one of interrupted transmission near the Gulf coast, two of ongoing transmission the smaller of which is near the Gulf of Mexico and the larger is on the border of Brazil) and , 1 area in Brazil (this area has ongoing transmission and is near the Venezuela border), and 1 area each in Colombia and Ecuador (both near the Pacific coast).

Geographic distribution and transmission status of Onchocerciasis in the Americas

The most recent PAHO resolution in 2009 called for OEPA and its partners, including CDC, to interrupt transmission in the region by 2012. Surveillance and certification activities will follow; the year 2017 is the current target date for certification of elimination of onchocerciasis in the Americas. Achieving this target date relies upon: an evidence-based action plan to interrupt transmission in the remaining areas of disease, post treatment surveillance, and continued financial donations from global partners.

A physician exams the eyes of a male Yanomami indian. The indians attend the clinic for diagnosis and treatment of onchocerciasis and malaria. Credit: WHO/TDR/Mark Edwards

A physician exams the eyes of a male Yanomami indian. The indians attend the clinic for diagnosis and treatment of onchocerciasis and malaria. Credit: WHO/TDR/Mark Edwards

A physician giving ivermectin tablets to those infected with onchocercal parasites. Credit: WHO/TDR/Mark Edwards

A physician giving ivermectin tablets to those infected with onchocercal parasites. Credit: WHO/TDR/Mark Edwards

As one of the major partners working to interrupt transmission, CDC is conducting laboratory research that will lead to treatment recommendations. The CDC-Universidad de Valle station in Guatemala is a regional reference laboratory that conducts serologic testing of children for the presence of onchocerciasis, in addition to DNA testing of blackflies for evidence of infection. These research activities monitor the success of treatment programs by indicating the presence and amount of infection in both the human and vector (blackfly) populations. Laboratory research in Guatemala is done in conjunction with the University of South Florida, an important collaborator in the elimination process.

Despite the program accomplishments, challenges still remain. For example, indigenous populations in the Amazon region of Venezuela and Brazil, specifically the Yanomami tribe, have been challenging to reach, as they are nomadic people and are difficult to locate and treat. However, based on recent research, this population could be treated as often as four times per year in an attempt to hasten the control of onchocerciasis. The remote areas where these populations live will require special attention and will undoubtedly be the last region in the Americas to interrupt transmission.

Partnerships are critical to achieve the target date for elimination of onchocerciasis in the Americas. Perhaps the most important partner is each country’s ministry of health. The ministries have taken leadership roles in the project, including providing close to 40% of the financial support needed to run the elimination program. Like so many other successful NTD programs, partnerships and collaborations are the foundation for success. Under the guidance of The Carter Center, working in conjunction with CDC, the Lions Club International, the Mectizan Donation Program, and the Pan American Health Organization, we will achieve elimination of onchocerciasis in the Americas by 2017. These partners will provide key assistance in using innovations developed as part of the program in the Americas to assist efforts against onchocerciasis in Africa. The success of control efforts thus far has allowed us to move the goal from control of morbidity to interruption of transmission and ultimately elimination of the parasite globally.