Transmission of Onchocerca volvulus continues in Nyagak-Bondo focus of northwestern Uganda after 18 years of a single dose of annual treatment with ivermectin.

The objective of the study was to determine whether annual ivermectin treatment in the Nyagak-Bondo onchocerciasis focus could safely be withdrawn. Baseline skin snip microfilariae (mf) and nodule prevalence data from six communities were compared with data collected in the 2011 follow-up in seven communities. Follow-up mf data in 607 adults and 145 children were compared with baseline (300 adults and 58 children). Flies collected in 2011 were dissected, and poolscreen analysis was applied to ascertain transmission. Nodule prevalence in adults dropped from 81.7% to 11.0% (P < 0.0001), and mf prevalence dropped from 97.0% to 23.2% (P < 0.0001). In children, mf prevalence decreased from 79.3% to 14.1% (P < 0.0001). Parous and infection rates of 401 flies that were dissected were 52.9% and 1.5%, respectively, whereas the infective rate on flies examination by polymerase chain reaction (PCR) was 1.92% and annual transmission potential was 26.9. Stopping ivermectin treatment may result in onchocerciasis recrudescence.

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.