Interruption of Onchocerca volvulus Transmission in the Abu Hamed Focus, Sudan

Abstract

Abstract. Abu Hamed, Sudan, the northernmost location of onchocerciasis in the world, began community-directed treatment with ivermectin (CDTI) in 1998, with annual treatments enhanced to semiannual in 2007. We assessed the status of the parasite transmission in 2011 entomologically, parasitologically, and serologically. O-150 pool screening showed no parasite DNA in 17,537 black flies collected in 2011 (95% confidence interval upper limit [95% CI UL] = 0.023). Skin microfilariae, nodules, and signs of skin disease were absent in 536 individuals in seven local communities. Similarly, no evidence of Onchocerca volvulus Ov16 antibodies was found in 6,756 school children 10 years (95% CI UL = 0.03%). Because this assessment of the focus meets the 2001 World Health Organization (WHO) criteria for interrupted transmission, treatment was halted in 2012, and a post-treatment surveillance period was initiated in anticipation of declaration of disease elimination in this area. We provide the first evidence in East Africa that long-term CDTI alone can interrupt transmission of onchocerciasis.

The First Confirmed Elimination of an Onchocerciasis Focus in Africa: Abu Hamed, Sudan

“…The number of samples collected and screened in this study complies with the limits set by WHO guidelines of at least 6,000 black flies and 2,000 blood spots per transmission zone. 16 Previously we reported the first evidence of interruption of O. volvulus transmission in Africa achieved with annual and semiannual ivermectin mass treatment alone in Abu Hamed in 2012, 14 and now provide evidence for the first elimination of onchocerciasis after PTS in Africa following the new WHO guidelines for verification of onchocerciasis transmission interruption and elimination 16 ; these guidelines are based on the successes in South America. [9][10][11] Our data meets the major recommendation of < 1% upper limit 95% CI of infection where no black flies screened by the O-150 PCR assay are infected, as well as the upper limit of the 95% CI of 0.1% for the prevalence of infection in children ≤ 10 years of age.…”

“…In this assessment, no infection was found in > 17,000 black flies screened by O-150 PCR, no antibodies to Ov16 antigen in 6,756 children ≤ 10 years of age, and no signs of infection in 536 adult individuals from seven communities within the focus. 14 This assessment indicated that the disease transmission has been interrupted in Abu Hamed based on the WHO 2001 guidelines for interruption of onchocerciasis transmission. 11 Review of these findings prompted the government of Sudan to declare interruption of the parasite transmission, halting mass treatment activities, and beginning a 3-year posttreatment surveillance (PTS) phase in May 2012 ( Figure 1B).…”

“…Other factors that assisted in the decision to stop treatment in 2012 and achievement of elimination status are the absence of lymphatic filariasis and the negligible chance of infected vectors or people migration into the Abu Hamed area due to its unique location and nature. 14 The onchocerciasis elimination activities in Abu Hamed had its share of challenges represented by displacement of communities impacted by Merowe dam and the potential for creation of new and perennial vector breeding sites in the spillway downstream of the dam. In this and a previous study, we have screened an 8-km area along the River Nile to verify absence of adult and aquatic stages of black flies.…”

“…Figure 1A). [13][14][15] Thus, a new breeding site near Al Sarsaf village west of the flooded area was added to the PTS assessment protocol. In addition, Hamdab Island, downstream of Merowe dam, was also monitored for the possible introduction of new black fly breeding sites due to favorable conditions created by the dam, and two displaced communities were screened in their new locations for any exposure to the infection.…”

Serosurveillance to Monitor Onchocerciasis Elimination: The Ugandan Experience

“…5 However, recent data have suggested that this is not the case, and that long-term community wide distribution of ivermectin may be capable of eliminating onchocerciasis in at least some foci in Africa. [6][7][8][9][10] This discovery has resulted in a refocusing of the international community from an emphasis on control of onchocerciasis in Africa toward an emphasis upon possible elimination. 11,12 Monitoring and evaluation activities are especially necessary in elimination efforts to document the effectiveness of program operations and eventually in showing that transmission had been interrupted.…”