Declining Onchocerca volvulus transmission despite limited ivermectin delivery in the Kakoi–Koda focus, Ituri, Democratic Republic of the Congo: An epidemiological, entomological and landscape evidence synthesis

@article{amaral2026declining,
  title = {{Declining Onchocerca volvulus transmission despite limited ivermectin delivery in the Kakoi–Koda focus, Ituri, Democratic Republic of the Congo: An epidemiological, entomological and landscape evidence synthesis}},
  author = {Luís-Jorge Amaral and Tony Ukety and Jules Upenjirwoth and Deogratias Ucima Wonya’Rossi and Michel Ndahura Mandro and Françoise Nyisi and Pascal Adroba and Wilma A. Stolk and Joseph N. Siewe Fodjo and María-Gloria Basáñez and Anne Laudisoit and Robert Colebunders},
  journal = {PLOS Neglected Tropical Diseases},
  year = {2026},
  month = aug,
  doi = {10.1371/journal.pntd.0014164},
  url = {https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014164},
  note = {CC BY 4.0},
}

TY  - JOUR
TI  - Declining Onchocerca volvulus transmission despite limited ivermectin delivery in the Kakoi–Koda focus, Ituri, Democratic Republic of the Congo: An epidemiological, entomological and landscape evidence synthesis
AU  - Luís-Jorge Amaral
AU  - Tony Ukety
AU  - Jules Upenjirwoth
AU  - Deogratias Ucima Wonya’Rossi
AU  - Michel Ndahura Mandro
AU  - Françoise Nyisi
AU  - Pascal Adroba
AU  - Wilma A. Stolk
AU  - Joseph N. Siewe Fodjo
AU  - María-Gloria Basáñez
AU  - Anne Laudisoit
AU  - Robert Colebunders
PY  - 2026
DA  - 2026/08/31
JO  - PLOS Neglected Tropical Diseases
DO  - 10.1371/journal.pntd.0014164
UR  - https://journals.plos.org/plosntds/article?id=10.1371/journal.pntd.0014164
AB  - Background: The Kakoi–Koda focus in Ituri Province was historically hyperendemic for onchocerciasis, yet screening for a recent trial suggested a marked decline, including in Logo Health Zone, which had never received routine ivermectin. We explored whether this decline extended across the focus and how infection indicators corresponded spatially with ivermectin delivery, entomological observations and deforestation. Methodology: We conducted a scoping evidence synthesis of epidemiological, programmatic, entomological and geospatial sources. Against a 2003 nodule-mapping baseline, change was assessed from repeated cross-sectional moxidectin trial screenings in 2010–11 and 2021–2023, which applied the same four-skin-snip protocol to community-recruited residents aged ≥12 years. Anti-Ov16 serology (2015–21), two-skin-snip surveys (2015/17), exploratory blackfly observations (2009–18) and remotely sensed tree-cover loss (2001–24) provided further contextual evidence. Principal findings: Between the two trial screenings, microfilarial prevalence significantly declined from 79.0% to 9.0% (Draju) and 68.9% to 8.6% (Kanga) in Logo, similar to declines observed in villages of Nyarambe Health Zone (72.2% to 2.9%), which received routine ivermectin for lymphatic filariasis. Mean infection intensity mirrored this pattern, from 17-26 to 1 microfilariae per milligram of skin in Logo, and 11 to 0.4 in Nyarambe. Seroprevalence in children aged 3–10 years from 2016 onward was low (0–5%), geographically circumscribed and broadly concordant with the skin-snip spatial pattern. Opportunistic blackfly collections and breeding-site prospections detected Simulium dentulosum and S. vorax as the current anthropophagic species, with no evidence of S. neavei after 2009. Extensive dense forest loss (75–90% in historically hyperendemic Logo) and canopy opening are consistent with a shift from crab-associated S. neavei habitats towards more open-habitat vectors, providing a plausible ecological mechanism. Significance: Parasitological, serological, entomological and geospatial evidence consistently indicates substantial declines in O. volvulus infection indicators across Kakoi-Koda, compatible with reduced transmission. Residual positive indicators were spatially circumscribed, including in Logo where no routine ivermectin was delivered. Whether the current simuliid species can sustain transmission above elimination thresholds remains uncertain. Standardised, representative surveys in the Muda/Kuda and Lebu River basins are warranted to guide decisions on starting and stopping ivermectin delivery. Author summary: Onchocerciasis, also known as river blindness, is a parasitic disease of public health concern in sub-Saharan Africa, transmitted by blackfly vectors. The disease is responsible for skin and eye clinical manifestations and is associated with neurological complications. We investigated an area in north-eastern Democratic Republic of the Congo called the Kakoi-Koda onchocerciasis focus, where the infection was common in the early 2000s. We reviewed and assembled data from past studies on infection in humans and blackflies, and analysed satellite imagery to assess the loss of tree cover that can affect where blackflies live and breed. We found that the prevalence of onchocerciasis in Kakoi-Koda has declined markedly in recent years. This decline appears to be linked to the deforestation of the habitat suitable for some blackfly species, and to ivermectin distribution to treat onchocerciasis in parts of the focus. Our findings help to understand why onchocerciasis has decreased across the Kakoi-Koda focus and highlight a number of fast-flowing river segments where certain blackfly species may allow small pockets of local transmission. These results support continued, targeted monitoring to determine whether the disease is still transmitted in specific locations, where elimination interventions may still be needed.
SN  - 1935-2735
ER  -