Transmission of Onchocerciasis in Wadelai Focus of Northwestern Uganda Has Been Interrupted and the Disease Eliminated

Wadelai, an isolated focus for onchocerciasis in northwest Uganda, was selected for piloting an onchocerciasis elimination strategy that was ultimately the precursor for countrywide onchocerciasis elimination policy. The Wadelai focus strategy was to increase ivermectin treatments from annual to semiannual frequency and expand geographic area in order to include communities with nodule rate of less than 20%. These communities had not been covered by the previous policy that sought to control onchocerciasis only as a public health problem. From 2006 to 2010, Wadelai program successfully attained ultimate treatment goal (UTG), treatment coverage of ≥90%, despite expanding from 19 to 34 communities and from 5,600 annual treatments to over 29,000 semiannual treatments. Evaluations in 2009 showed no microfilaria in skin snips of over 500 persons examined, and only 1 of 3011 children was IgG4 antibody positive to the OV16 recombinant antigen. No Simulium vectors were found, and their disappearance could have sped up interruption of transmission. Although twice-per-year treatment had an unclear role in interruption of transmission, the experience demonstrated that twice-per-year treatment is feasible in the Ugandan setting. The monitoring data support the conclusion that onchocerciasis has been eliminated from the Wadelai focus of Uganda. 1. Introduction The Wadelai onchocerciasis focus is one of the smallest in Uganda, comprising only about 15,000 people living close to the lower River Ora in the Nebbi district. It is not clear when this focus first came to the attention of the health authorities, but in 1951 onchocerciasis was recognised in the upper reaches of the River Aroga (a major tributary of the River Ora). The vector was assumed to be Simulium neavei [1] based on the forested environment. Much more was learnt of the distribution of onchocerciasis and its vectors in the following two decades. The breeding of a non-man-biting form of S. damnosum s.l, was reported in 1966 along River Ali, located opposite Rhino Camp roughly 15 kilometres downstream of the River Ora outfall [2, 3]. Barnley in his lecture notes delivered at Makerere University in 1968 entitled “The Distribution of Onchocerciasis and its Vectors in Uganda”, confirmed that S. neavei was the vector in the upper reaches of River Ora system, but made no mention of the situation in its lower reaches where the Wadelai focus is located [4]. Later in the Uganda Atlas of disease distribution, Barnley gave a distribution map of onchocerciasis and its vectors showing the presence of a small